1 - Basics of Java
Explain features of JAVA.
Features of java is discussed below:
 Simple
Java was designed to be easy for the professional programmer to learn and use effectively. Java
is easy to master. If we have Basic concepts of object-oriented programming, learning Java will
be even easier. Best of all, if you are an experienced C++ programmer, moving to Java will
require very little effort. Because Java inherits the C/C++ syntax and many of the object
oriented features of C++, most programmers have little trouble learning Java.
 Object-Oriented
Java was not designed to be source-code compatible with any other language. This allowed the
Java team the freedom to design with a blank slate. One outcome of this was a clean, usable,
pragmatic approach to objects.
 Robust
o The multiplatformed environment of the Web places extraordinary demands on a program,
because the program must execute reliably in a variety of systems. Thus, the ability to
create robust programs was given a high priority in the design of Java. To gain reliability,
Java restricts you in a few key areas to force you to find your mistakes early in program
development. At the same time, Java frees us from having to worry about many of the most
common causes of programming errors.
o Because Java is a strictly typed language, it checks your code at compile time. However, it
also checks your code at run time. Many hard-to-track-down bugs that often turn up in
hard-to reproduce run-time situations are simply impossible to create in Java. Knowing that
what you have written will behave in a predictable way under diverse conditions is a key
feature of Java.
o To better understand how Java is robust, consider two of the main reasons for program
failure: memory management mistakes and mishandled exceptional conditions (that is, runtime errors). Memory management can be a difficult, tedious task in traditional
programming environments.
 Multithreaded
Java was designed to meet the real-world requirement of creating interactive, networked
programs. To accomplish this, Java supports multithreaded programming, which allows you to
write programs that do many things simultaneously. The Java run-time system comes with an
elegant yet sophisticated solution for multiprocess synchronization that enables you to
construct smoothly running interactive systems. Java’s easy-to-use approach to multithreading
allows you to think about the specific behavior of your program, not the multitasking
subsystem.
 Architecture-Neutral
Acentral issue for the Java designers was that of code longevity and portability. One of the main
problems facing programmers is that no guarantee exists that if you write a program today, it
will run tomorrow—even on the same machine. Operating system upgrades, processor
upgrades, and changes in core system resources can all combine to make a program
malfunction. The Java designers made several hard decisions in the Java language and the Java
Virtual Machine in an attempt to alter this situation.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
1
1 - Basics of Java



Interpreted and High Performance
Java enables the creation of cross-platform programs by compiling into an intermediate
representation called Java bytecode. This code can be executed on any system that implements
the Java Virtual Machine. Most previous attempts at cross-platform solutions have done so at
the expense of performance. As explained earlier, the Java bytecode was carefully designed so
that it would be easy to translate directly into native machine code for very high performance
by using a just-in-time compiler. Java run-time systems that provide this feature lose none of
the benefits of the platform-independent code.
Distributed
Java is designed for the distributed environment of the Internet because it handles TCP/IP
protocols. In fact, accessing a resource using a URL is not much different from accessing a file.
Java also supports Remote Method Invocation (RMI). This feature enables a program to invoke
methods across a network.
Dynamic
Java programs carry with them substantial amounts of run-time type information that is used to
verify and resolve accesses to objects at run time. This makes it possible to dynamically link
code in a safe and expedient manner. This is crucial to the robustness of the Java environment,
in which small fragments of bytecode may be dynamically updated on a running system.
Explain Operators in JAVA.
Arithmetic Operator
Operator Description
+
*
/
%
++
--
Example
Addition - Adds values on either side of the operator
A + B will give
30
Subtraction - Subtracts right hand operand from left hand operand
A - B will give
-10
Multiplication - Multiplies values on either side of the operator
A * B will give
200
Division - Divides left hand operand by right hand operand
B / A will give 2
Modulus - Divides left hand operand by right hand operand and B % A will give 0
returns remainder
Increment - Increases the value of operand by 1
B++ gives 21
Decrement - Decreases the value of operand by 1
B-- gives 19
Arithmetic Operators in JAVA, consider A as 10 & B as 20
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
2
1 - Basics of Java
Relational Operators
Operator Description
Example
==
Checks if the values of two operands are equal or not, if yes then (A == B) is not
condition becomes true.
true.
!=
>
<
>=
<=
Checks if the values of two operands are equal or not, if values are not
equal then condition becomes true.
Checks if the value of left operand is greater than the value of right
operand, if yes then condition becomes true.
Checks if the value of left operand is less than the value of right
operand, if yes then condition becomes true.
Checks if the value of left operand is greater than or equal to the value
of right operand, if yes then condition becomes true.
Checks if the value of left operand is less than or equal to the value of
right operand, if yes then condition becomes true.
(A != B) is
true.
(A > B) is not
true.
(A < B) is true.
(A >= B) is not
true.
(A <= B) is
true.
Relational Operators in JAVA, consider A as 10 & B as 20
Bitwise Operators
Operator Description
&
Binary AND Operator copies a bit to the result if it
exists in both operands.
|
Binary OR Operator copies a bit if it exists in either
operand.
Example
(A & B) will give 12 which is 0000
1100
(A | B) will give 61 which is 0011
1101
^
Binary XOR Operator copies the bit if it is set in one (A ^ B) will give 49 which is 0011
operand but not both.
0001
~
Binary Ones Complement Operator is unary and has (~A ) will give -61 which is 1100
the effect of 'flipping' bits.
0011 in 2's complement form due
to a signed binary number.
Binary Left Shift Operator. The left operands value A << 2 will give 240 which is 1111
is moved left by the number of bits specified by the 0000
right operand.
Binary Right Shift Operator. The left operands value A >> 2 will give 15 which is 1111
is moved right by the number of bits specified by
the right operand.
<<
>>
>>>
Shift right zero fill operator. The left operands value A >>>2 will give 15 which is 0000
is moved right by the number of bits specified by 1111
the right operand and shifted values are filled up
with zeros.
Bitwise Operators in JAVA, consider A as 60 & B as 13
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
3
1 - Basics of Java
Logical Operators
Operator Description
&&
Called Logical AND operator. If both the operands are non-zero, then the
condition becomes true.
||
Called Logical OR Operator. If any of the two operands are non-zero,
then the condition becomes true.
!
Called Logical NOT Operator. Use to reverses the logical state of its
operand. If a condition is true then Logical NOT operator will make false.
Example
(A && B) is
false.
(A || B) is
true.
!(A && B) is
true.
Logical Operators in JAVA, consider A as true & B as false
Assignment Operators
Operator Description
Example
=
Simple assignment operator, Assigns values from right side C = A + B will assign
operands to left side operand
value of A + B into C
+=
<<=
Add AND assignment operator, It adds right operand to the
left operand and assign the result to left operand
Subtract AND assignment operator, It subtracts right operand
from the left operand and assign the result to left operand
Multiply AND assignment operator, It multiplies right
operand with the left operand and assign the result to left
operand
Divide AND assignment operator, It divides left operand with
the right operand and assign the result to left operand
Modulus AND assignment operator, It takes modulus using
two operands and assign the result to left operand
Left shift AND assignment operator
>>=
Right shift AND assignment operator
&=
Bitwise AND assignment operator
^=
bitwise exclusive OR and assignment operator
|=
bitwise inclusive OR and assignment operator
-=
*=
/=
%=
C += A is equivalent to C
=C+A
C -= A is equivalent to C
=C-A
C *= A is equivalent to C
=C*A
C /= A is equivalent to C
=C/A
C %= A is equivalent to
C=C%A
C <<= 2 is same as C = C
<< 2
C >>= 2 is same as C = C
>> 2
C &= 2 is same as C = C
&2
C ^= 2 is same as C = C ^
2
C |= 2 is same as C = C |
2
Assignment Operators in JAVA
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
4
1 - Basics of Java
Explain short circuit operators.





Java provides two interesting Boolean operators not found in many other computer languages.
These are secondary versions of the Boolean AND and OR operators, and are known as
shortcircuit logical operators.
The OR operator results in true when A is true, no matter what B is. Similarly, the AND operator
results in false when A is false, no matter what B is. If you use the || and && forms, rather than
the | and & forms of these operators, Java will not bother to evaluate the right-hand operand
when the outcome of the expression can be determined by the left operand alone.
This is very useful when the right-hand operand depends on the value of the left one in order to
function properly. For example, the following code fragment shows how you can take
advantage of short-circuit logical evaluation to be sure that a division operation will be valid
before evaluating it:
if (denom != 0 && num / denom > 10)
Since the short-circuit form of AND (&&) is used, there is no risk of causing a run-time exception
when denom is zero. If this line of code were written using the single & version of AND, both
sides would be evaluated, causing a run-time exception when denom is zero. It is standard
practice to use the short-circuit forms of AND and OR in cases involving Boolean logic, leaving
the single-character versions exclusively for bitwise operations. However, there are exceptions
to this rule. For example, consider the following statement:
if(c==1 & e++ < 100) d = 100)
Here, using a single & ensures that the increment operation will be applied to e whether c is
equal to 1 or not.
Explain primitive Data types of JAVA.
Java defines 8 primitive types:
 byte
o Smallest integer type
o It is a signed 8-bit type (1 Byte)
o Range is -128 to 127
o Especially useful when working with stream of data from a network or file
o Example:
byte b = 10;
 short
o short is signed 16-bit (2 Byte) type
o Range : -32768 to 32767
o It is probably least used Java type
o Example:
short vId = 1234;
 int
o The most commonly used type
o It is signed 32-bit (4 Byte) type
o Range: -2,147,483,648 to 2,147,483,647
o Example:
int a = 1234;
 long
o long is signed 64-bit (8 Byte) type
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
5
1 - Basics of Java




o It is useful when int type is not large enough to hold the desired value
o Example:
long soconds = 1234124231;
char
o It is 16-bit (2 Byte) type
o Range: 0 to 65,536
o Example:
char first = ‘A’;
char second = 65;
float
o It is 32-bit (4-Byte) type
o It specifies a single-precision value
o Example:
float price = 1234.45213f
double
o It uses 64-bit (8-Byte)
o All math functions such as sin(),cos(),sqrt() etc… returns double value
o Example:
double pi = 3.14141414141414;
boolean
o The boolean data type has only two possible values: true and false.
o This data type represents one bit of information, but its "size" isn't something that's
precisely defined.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
6
2 – Array & String
Arrays in Java

One-Dimensional Arrays
A One-dimensional array is essentially a list of like-typed variables.
Array declaration:
type var-name[];
Example:
Int student_marks[];
Above example will represent array with no value (null) To link student_marks with actual,
physical array of integers, we must allocate one using new keyword.
Example:
int student_marks[] = new int[20];

Multi-Dimensional Arrays
A In java, Multidimensional arrays are actually array of arrays.
Example:
int runPerOver[][] = new int[50][6];
Manually allocate different size:
Int runPerOver[][] = new int[3][];
runPerOver[0] = new int[6];
runPerOver[1] = new int[7];
runPerOver[2] = new int[6];
Initialization :
Int runPerOver[][] = {
{0,4,2,1,0,6},
{1,56,4,1,2,4,0},
{6,4,1,0,2,2},
}
Explain String Class in JAVA.





An object of the String class represents a string of characters.
The String class belongs to the java.lang package, which does not require an import statement.
Like other classes, String has constructors and methods.
Unlike other classes, String has two operators, + and += (used for concatenation).
Immutability:
o Once created, a string cannot be changed: none of its methods changes the string.
o Such objects are called immutable.
o Immutable objects are convenient because several references can point to the same
object safely: there is no danger of changing an object through one reference
without the others being aware of the change.
o Advantages Of Immutability
 Uses less memory.
o Disadvantages of Immutability
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
7
2 – Array & String



Less efficient — you need to create a new string and throw away the old one
even for small changes.
Empty Strings:
o An empty String has no characters. It’s length is 0.
String word1 = "";
String word2 = new String();
 Not the same as an uninitialized String (null string)
private String errorMsg;
Copy Constructors :
o Copy constructor creates a copy of an existing String. Also rarely used.
o Not the same as an assignment.
o Copy Constructor: Each variable points to a different copy of the String.
o Assignment: Both variables point to the same String.


Other Constructors :
o Most other constructors take an array as a parameter to create a String.
 char[] letters = {‘J’, ‘a’, ‘v’, ‘a’};
 String word = new String(letters);
Methods of String Class in JAVA :
Method
Description
char charAt(int index)
charAt() function returns the character located at the
specified index.
int indexOf(char ch)
Returns the index within this string of the first occurrence of
the specified character.
int compareTo(String o) Compares this String to another Object.
String concat(String str) Concatenates the specified string to the end of this string.
int length()
The string length() method returns length of the string.
String trim()
The string trim() method eliminates white spaces before
and after string.
String replace(char oc, The string replace() method replaces all occurrence of first
char nc)
sequence of character with second sequence of character.
toUpperCase()
The java string toUpperCase() method converts this string
into uppercase letter.
toLowerCase()
string toLowerCase() method into lowercase letter.
Explain StringBuffer Class in JAVA.

The java.lang.StringBuffer class is a thread-safe, mutable sequence of characters. Following are
the important points about StringBuffer:
o A string buffer is like a String, but can be modified.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
8
2 – Array & String


o It contains some particular sequence of characters, but the length and content of the
sequence can be changed through certain method calls.
o They are safe for use by multiple threads.
o Every string buffer has a capacity.
Class constructors
Sr. No. Constructor & Description
1
StringBuffer()
This constructs a string buffer with no characters in it and an initial capacity of 16
characters.
2
StringBuffer(CharSequence seq)
This constructs a string buffer that contains the same characters as the specified
CharSequence.
3
StringBuffer(int capacity)
This constructs a string buffer with no characters in it and the specified initial capacity.
4
StringBuffer(String str)
This constructs a string buffer initialized to the contents of the specified string.
Here are some of the important methods of StringBuffer class.
o append(arg)
o delete(start index,end index)
o deleteCharAt(index)
o insert(index,arg)
o replace(start index,end index,arg)
o setCharAt(index,newchar)
o reverse()
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
9
3 – Classes, Objects and Methods
Classes in Java.


A class is a blue print from which individual objects are created.
A sample of a class is given below:
public class Dog{
String breed;
int age;
String color;
void barking(){
}
void hungry(){
}
void sleeping(){
}
}


A class can contain any of the following variable types.
o Local variables: Variables defined inside methods, constructors or blocks are called local
variables. The variable will be declared and initialized within the method and the variable
will be destroyed when the method has completed.
o Instance variables: Instance variables are variables within a class but outside any method.
These variables are instantiated when the class is loaded. Instance variables can be accessed
from inside any method, constructor or blocks of that particular class.
o Class variables: Class variables are variables declared with in a class, outside any method,
with the static keyword.
A class can have any number of methods to access the value of various kinds of methods. In the
above example, barking(), hungry() and sleeping() are methods.
Objects in Java.






Objects have states and behaviors. Example: A dog has states - color, name, breed as well as
behaviors -wagging, barking, eating. An object is an instance of a class.
Let us now look deep into what are objects. If we consider the real-world we can find many
objects around us, Cars, Dogs, Humans, etc. All these objects have a state and behavior.
If we consider a dog, then its state is - name, breed, color, and the behavior is - barking,
wagging, running
If you compare the software object with a real world object, they have very similar
characteristics.
Software objects also have a state and behavior. A software object's state is stored in fields and
behavior is shown via methods.
So in software development, methods operate on the internal state of an object and the objectto-object communication is done via methods.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
10
3 – Classes, Objects and Methods
Constructor in Java.



Every class has a constructor. If we do not explicitly write a constructor for a class the Java
compiler builds a default constructor for that class.
Each time a new object is created, at least one constructor will be invoked. The main rule of
constructors is that they should have the same name as the class. A class can have more than
one constructor.
Example of a constructor is given below:
public class Puppy{
public Puppy(){
}
public Puppy(String name){
// This constructor has one parameter, name.
}
}
Method overloading.




In Java it is possible to define two or more methods within the same class that share the same
name, as long as their parameter declarations are different. When this is the case, the methods
are said to be overloaded, and the process is referred to as method overloading.
When an overloaded method is invoked, Java uses the type and/or number of arguments as its
guide to determine which version of the overloaded method to actually call. Thus, overloaded
methods must differ in the type and/or number of their parameters. While overloaded methods
may have different return types, the return type alone is insufficient to distinguish two versions
of a method.
When Java encounters a call to an overloaded method, it simply executes the version of the
method whose parameters match the arguments used in the call.
Example of Method Overloading by changing the no. of arguments:
class Calculation{
void sum(int a,int b){
System.out.println(a+b);
}
void sum(int a,int b,int c){
System.out.println(a+b+c);
}
public static void main(String args[]){
Calculation obj=new Calculation();
obj.sum(10,10,10);
obj.sum(20,20);
}
}
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
11
3 – Classes, Objects and Methods

Example of Method Overloading by changing data type of argument
class Calculation2{
void sum(int a,int b){
System.out.println(a+b);
}
void sum(double a,double b){
System.out.println(a+b);
}
public static void main(String args[]){
Calculation2 obj=new Calculation2();
obj.sum(10.5,10.5);
obj.sum(20,20);
}
}
this keyword.


Java defines the this keyword. this can be used inside any method to refer to the current object.
this is always a reference to the object on which the method was invoked.
To better understand what this refers to, consider the following version of Box( ):
// A redundant use of this.
Box(double w, double h, double d) {
this. width = w;
this. height = h;
this. depth = d;
}


The use of this is redundant, but perfectly correct. Inside Box( ), this will always refer to the
invoking object.
While it is redundant in this case, this is useful in other contexts,
Box(double width, double height, double depth) {
this.width = width;
this.height = height;
this.depth = depth;
}
static keyword.



Static means one per class, not one for each object no matter how many instance of a class
might exist.
This means that you can use them without creating an instance of a class.Static methods are
implicitly
final, because overriding is done based on the type of the object, and static methods are
attached to a class, not an object.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
12
3 – Classes, Objects and Methods


A static method in a superclass can be shadowed by another static method in a subclass, as long
as the original method was not declared final. However, you can't override a static method with
a nonstatic method.
In other words, you can't change a static method into an instance method in a subclass.
Access Control in java.
Modifier
Same Class
Same Package
Subclass
Universe
Private
Default
Protected
Public
Nested Classes & Inner Classes in Java.






Java inner class or nested class is a class i.e. declared inside the class or interface.
Inner class is a part of nested class. Non-static nested classes are known as inner classes.
We use inner classes to logically group classes and interfaces in one place so that it can be more
readable and maintainable.
Additionally, it can access all the members of outer class including private data members and
methods.
Syntax of Inner class:
class Java_Outer_class{
//code
class Java_Inner_class{
//code
}
}
Advantage of java inner classes
There are basically three advantages of inner classes in java. They are as follows:
1. Nested classes represent a special type of relationship that is it can access all the
members (data members and methods) of outer class including private.
2. Nested classes are used to develop more readable and maintainable code because it
logically group classes and interfaces in one place only.
3. Code Optimization: It requires less code to write.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
13
3 – Classes, Objects and Methods
Abstract Class.








A Java abstract class is a class which cannot be instantiated, meaning you cannot create new
instances of an abstract class.
The purpose of an abstract class is to function as a base for subclasses.
Declaring an Abstract Class in Java
public abstract class MyAbstractClass {
}
Abstract Methods:
An abstract class can have abstract methods. You declare a method abstract by adding the
abstract keyword in front of the method declaration. Here is a Java abstract method
example:
public abstract class MyAbstractClass {
public abstract void abstractMethod();
}
An abstract method has no implementation. It just has a method signature. Just like methods in
a Java interface.
If a class has an abstract method, the whole class must be declared abstract. Not all methods in
an abstract class have to be abstract methods. An abstract class can have a mixture of abstract
and non-abstract methods.
Subclasses of an abstract class must implement (override) all abstract methods of its abstract
superclass. The non-abstract methods of the superclass are just inherited as they are. They can
also be overridden, if needed.
The Purpose of Abstract Classes:
The purpose of abstract classes is to function as base classes which can be extended by
subclasses to create a full implementation.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
14
4 – Inheritance and Interfaces
Inheritance in Java






Inheritance in java is a mechanism in which one object acquires all the properties and behaviors
of parent object.
The idea behind inheritance in java is that you can create new classes that are built upon
existing classes.
When you inherit from an existing class, you can reuse methods and fields of parent class, and
you can add new methods and fields also.
Inheritance represents the IS-A relationship, also known as parent-child relationship.
Why use inheritance in java
o For Method Overriding (so runtime polymorphism can be achieved).
o For Code Reusability.
Syntax of Java Inheritance
class Subclass-name extends Superclass-name
{
//methods and fields
}




The extends keyword indicates that you are making a new class that derives from an existing
class.
In the terminology of Java, a class that is inherited is called a super class. The new class is called
a subclass.
example of inheritance
As displayed in the above figure, Programmer is the subclass and Employee is the superclass.
Relationship between two classes is Programmer IS-A Employee.It means that Programmer is a
type of Employee.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
15
4 – Inheritance and Interfaces
class Employee{
float salary=40000;
}
class Programmer extends Employee{
int bonus=10000;
public static void main(String args[]){
Programmer p=new Programmer();
System.out.println("Programmer salary is:"+p.salary);
System.out.println("Bonus of Programmer is:"+p.bonus);
}
}

Types of inheritance in java
o On the basis of class, there can be three types of inheritance in java: single, multilevel and
hierarchical.
o In java programming, multiple and hybrid inheritance is supported through interface only.

Multiple inheritance and Hybrid inheritance is not supported in java through class.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
16
4 – Inheritance and Interfaces
Why multiple inheritance is not supported in java?



To reduce the complexity and simplify the language, multiple inheritance is not supported in
java.
Consider a scenario where A, B and C are three classes. The C class inherits A and B classes. If A
and B classes have same method and you call it from child class object, there will be ambiguity
to call method of A or B class.
Since compile time errors are better than runtime errors, java renders compile time error if you
inherit 2 classes. So whether you have same method or different, there will be compile time
error now.
class A{
void msg(){System.out.println("Hello");}
}
class B{
void msg(){System.out.println("Welcome");}
}
class C extends A,B{//suppose if it were
public static void main(String args[]){
C obj=new C();
obj.msg();//Now which msg() method would be invoked?
}
}
Method Overriding


In a class hierarchy, when a method in a subclass has the same name and type signature as a
method in its superclass, then the method in the subclass is said to override the method in the
superclass.
When an overridden method is called from within a subclass, it will always refer to the version
of that method defined by the subclass. The version of the method defined by the superclass
will be hidden. Consider the following:
// Method overriding.
class A {
int i, j;
A(int a, int b) {
i = a;
j = b;
}
// display i and j
void show() {
System.out.println("i and j: " + i + " " + j);
}
}
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
17
4 – Inheritance and Interfaces
class B extends A {
int k;
B(int a, int b, int c) {
super(a, b);
k = c;
}
// display k – this overrides show() in A
void show() {
System.out.println("k: " + k);
}
}
class Override {
public static void main(String args[]) {
B subOb = new B(1, 2, 3);
subOb.show(); // this calls show() in B
}
}
Final keyword


The final keyword in java is used to restrict the user.
The final keyword can be used in many contexts. Final can be:
1. Variable
If you make any variable as final, you cannot change the value of final variable (It will be
constant).
Example:
class Bike9{
final int speedlimit=90;//final variable
void run(){
speedlimit=400;
}
public static void main(String args[]){
Bike9 obj=new Bike9();
obj.run();
}
}
Output: Compile Time Error
2. Method
If you make any method as final, you cannot override it.
Example:
class Bike{
final void run(){System.out.println("running");}
}
class Honda extends Bike{
void run(){
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
18
4 – Inheritance and Interfaces
System.out.println("running safely with 100kmph");
}
public static void main(String args[]){
Honda honda= new Honda();
honda.run();
}
}
Output: Compile Time Error
3. Class
If you make any class as final, you cannot extend it.
Example:
final class Bike{
// code here
}
class Honda1 extends Bike{
void run(){System.out.println("running safely with 100kmph");}
public static void main(String args[]){
Honda1 honda= new Honda();
honda.run();
}
}
Output: Compile Time Error
Interface in java.






Using the keyword interface, you can fully abstract a class’ interface from its implementation.
That is, using interface, you can specify what a class must do, but not how it does it.
Interfaces are syntactically similar to classes, but they lack instance variables, and their methods
are declared without any body.
In practice, this means that you can define interfaces that don’t make assumptions about how
they are implemented.
Once it is defined, any number of classes can implement an interface. Also, one class can
implement any number of interfaces.
Syntax of interface:
// interface syntax.
Interface myInterface
{
int a=10;
public int getBalance();
public void setBalance(int a);
}
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
19
4 – Inheritance and Interfaces





To implement an interface, a class must create the complete set of methods defined by the
interface. However, each class is free to determine the details of its own implementation.
By providing the interface keyword, Java allows you to fully utilize the “one interface, multiple
methods” aspect of polymorphism.
Interfaces are designed to support dynamic method resolution at run time.
Normally, in order for a method to be called from one class to another, both classes need to be
present at compile time so the Java compiler can check to ensure that the method signatures
are compatible.
All the variables defined in the interface are default final and cannot be changed in subclass.
instanceof keyword.






Sometimes, knowing the type of an object during run time is useful. For example, you might
have one thread of execution that generates various types of objects, and another thread that
processes these objects.
In this situation, it might be useful for the processing thread to know the type of each object
when it receives it. Another situation in which knowledge of an object’s type at run time is
important involves casting.
In Java, an invalid cast causes a run-time error. Many invalid casts can be caught at compile
time. However, casts involving class hierarchies can produce invalid casts that can be detected
only at run time.
For example, a superclass called A can produce two subclasses, called B and C. Thus, casting a B
object into type A or casting a C object into type A is legal, but casting a B object into type C (or
vice versa) isn’t legal. Because an object of type A can refer to objects of either B or C, how can
you know, at run time, what type of object is actually being referred to before attempting the
cast to type C? It could be an object of type A, B, or C. If it is an object of type B, a run-time
exception will be thrown. Java provides the run-time operator instanceof to answer this
question.
The instanceof operator has this general form:
object instanceof type
The following program demonstrates instanceof:
class A
{
public static void main(String[] ar)
{
String a = “hello”;
Double d = new Double(10.0);
If(a instanceof String)
{
System.out.println(“A is a instance of String”);
}
If(d instanceof Object)
{
System.out.println(“D is a instance of Object”);
}
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
20
4 – Inheritance and Interfaces
}
}
Dynamic Method Dispatch.




Method overriding forms the basis for one of Java’s most powerful concepts: dynamic method
dispatch. Dynamic method dispatch is the mechanism by which a call to an overridden method
is resolved at run time, rather than compile time. Dynamic method dispatch is important
because this is how Java implements run-time polymorphism.
Let’s begin by restating an important principle: a superclass reference variable can refer to a
subclass object. Java uses this fact to resolve calls to overridden methods at run time. Here is
how. When an overridden method is called through a superclass reference, Java determines
which version of that method to execute based upon the type of the object being referred to at
the time the call occurs. Thus, this determination is made at run time. When different types of
objects are referred to, different versions of an overridden method will be called.
In other words, it is the type of the object being referred to (not the type of the reference
variable) that determines which version of an overridden method will be executed. Therefore, if
a superclass contains a method that is overridden by a subclass, then when different types of
objects are referred to through a superclass reference variable, different versions of the
method are executed.
Here is an example that illustrates dynamic method dispatch:
// Dynamic Method Dispatch
class A {
void callme() {
System.out.println("Inside A's callme method");
}
}
class B extends A {
// override callme()
void callme() {
System.out.println("Inside B's callme method");
}
}
class C extends A {
// override callme()
void callme() {
System.out.println("Inside C's callme method");
}
}
class Dispatch {
public static void main(String args[]) {
A a = new A(); // object of type A
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
21
4 – Inheritance and Interfaces
B b = new B(); // object of type B
C c = new C(); // object of type C
A r; // obtain a reference of type A
r = a; // r refers to an A object
r.callme(); // calls A's version of callme
r = b; // r refers to a B object
r.callme(); // calls B's version of callme
r = c; // r refers to a C object
r.callme(); // calls C's version of callme
}
}
Output:
Inside A’s callme method
Inside B’s callme method
Inside C’s callme method

This program creates one superclass called A and two subclasses of it, called B and C. Subclasses
B and C override callme( ) declared in A. Inside the main( ) method, objects of type A, B, and C
are declared. Also, a reference of type A, called r, is declared. The program then in turn assigns
a reference to each type of object to r and uses that reference to invoke callme( ). As the output
shows, the version of callme( ) executed is determined by the type of object being referred to at
the time of the call. Had it been determined by the type of the reference variable, r, you would
see three calls to A’s callme( ) method.
Comparison between Abstract Class and interface.
Abstract Class
A Java abstract class can have instance
methods that implement a default
behavior.
An abstract class may contain non-final
variables.
A Java abstract class can have the
usual flavors of class members like
private, protected, etc..
A Java abstract class should be
extended using keyword “extends”.
A Java class can extend only one
abstract class.
Interface
Java interface are implicitly abstract
and cannot have implementations
Variables declared in a Java interface is
by default final
Members of a Java interface are public
by default
Java interface should be implemented
using keyword “implements”.
A Java class can implement multiple
interfaces
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
22
5 – Package
Use of Package




Packages are used in Java in order to prevent naming conflicts, to control access, to make
searching/locating and usage of classes, interfaces, enumerations and annotations easier, etc.
A Package can be defined as a grouping of related types(classes, interfaces, enumerations and
annotations ) providing access protection and name space management.
Programmers can define their own packages to bundle group of classes/interfaces, etc. It is a
good practice to group related classes implemented by you so that a programmer can easily
determine that the classes, interfaces, enumerations, annotations are related.
Since the package creates a new namespace there won't be any name conflicts with names in
other packages. Using packages, it is easier to provide access control and it is also easier to
locate the related classes.
Creating a package:




When creating a package, you should choose a name for the package and put a package
statement with that name at the top of every source file that contains the classes, interfaces,
enumerations, and annotation types that you want to include in the package.
The package statement should be the first line in the source file. There can be only one package
statement in each source file, and it applies to all types in the file.
If a package statement is not used then the class, interfaces, enumerations, and annotation
types will be put into an unnamed package.
Example:
package animals;
interface Animal {
public void eat();
}
The import Keyword:


If a class wants to use another class in the same package, the package name does not need to
be used. Classes in the same package find each other without any special syntax.
Example:
import animals.Animal;
// OR import animals.*; to import all the classes in the animals package
public class Dog implements Animal
{
public void ear()
{
// Code Here
}
}
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
23
5 – Package
Set CLASSPATH System Variable:



To display the current CLASSPATH variable, use the following commands in Windows and UNIX
(Bourne shell):
o In Windows -> C:\> set CLASSPATH
o In UNIX -> % echo $CLASSPATH
To delete the current contents of the CLASSPATH variable, use :
o In Windows -> C:\> set CLASSPATH=
o In UNIX -> % unset CLASSPATH; export CLASSPATH
To set the CLASSPATH variable:
o In Windows -> set CLASSPATH=C:\users\jack\java\classes
o In UNIX -> % CLASSPATH=/home/jack/java/classes; export CLASSPATH
Static Import:




The static import feature of Java 5 facilitate the java programmer to access any static member
of a class directly. There is no need to qualify it by the class name.
Advantage of static import:
o Less coding is required if you have access any static member of a class oftenly.
Disadvantage of static import:
o If you overuse the static import feature, it makes the program unreadable and
unmaintainable.
Example of static import:
import static java.lang.System.*;
class StaticImportExample{
public static void main(String args[]){
out.println("Hello");//Now no need of System.out
out.println("Java");
}
}
What is the difference between import and static import?
The import allows the java programmer to access classes of a package without package
qualification whereas the static import feature allows to access the static members of a
class without the class qualification. The import provides accessibility to classes and
interface whereas static import provides accessibility to static members of the class.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
24
6 – Exception Handling
Difference between error and exception

Errors and exceptions both inherit from Throwable, but they differ in these ways:
Exceptions
Errors
 Any departure from the expected  Any error or problem which one can
behavior of the system or program,
handle and continue to work
which stops the working of the system
normally.
is an error.
 Can be checked or unchecked
 Are always unchecked
 Indicate an error caused by the  Usually indicate a system error or a
programmer
problem with a low-level resource
 Should be handled at the application  Should be handled at the system
level
level, if possible
Checked and Unchecked Exceptions.
Exceptions in Java are classified on the basis of the exception handled by the java compiler. Java
consists of the following type of built in exceptions:

Checked Exception: These exception are the object of the Exception class or any of its
subclasses except Runtime Exception class. These condition arises due to invalid input, problem
with your network connectivity and problem in database.java.io.IOException is a checked
exception. This exception is thrown when there is an error in input-output operation. In this
case operation is normally terminated.
o List of Checked Exceptions
Exception
Reason for Exception
This Exception occurs when Java runClassNotFoundException
time system fail to find the specified
class mentioned in the program
This Exception occurs when you
Instantiation Exception
create an object of an abstract class
and interface
This Exception occurs when you
Illegal Access Exception
create an object of an abstract class
and interface
This Exception occurs when the
Not Such Method Exception method you call does not exist in
class
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
25
6 – Exception Handling

Unchecked Exception: These Exception arises during run-time ,that occur due to invalid
argument passed to method. The java Compiler does not check the program error during
compilation. For Example when you divide a number by zero, run-time exception is raised.
o List of Unchecked Exceptions
Exception
Reason for Exception
These Exception occurs, when you
Arithmetic Exception
divide a number by zero causes an
Arithmetic Exception
These Exception occurs, when you
Array Store Exception
assign an array which is not compatible
with the data type of that array
These Exception occurs, when you
Array Index Out Of Bounds
assign an array which is not compatible
Exception
with the data type of that array
These Exception occurs, when you try
to implement an application without
Null Pointer Exception
referencing the object and allocating
to a memory
These Exception occurs, when you try
to convert a string variable in an
Number Format Exception
incorrect format to integer (numeric
format) that is not compatible with
each other
Explain use of throw.




It is possible for your program to throw an exception explicitly, using the throw statement. The
general form of throw is shown here:
throw ThrowableInstance;
Here, ThrowableInstance must be an object of type Throwable or a subclass of Throwable.
Primitive types, such as int or char, as well as non-Throwable classes, such as String and Object,
cannot be used as exceptions.
There are two ways you can obtain a Throwable object:
o using a parameter in a catch clause, or creating one with the new operator. The flow of
execution stops immediately after the throw statement; any subsequent statements are
not executed. The nearest enclosing try block is inspected to see if it has a catch
statement that matches the type of exception. If it does find a match, control is
transferred to that statement. If not, then the next enclosing try statement is inspected,
and so on. If no matching catch is found, then the default exception handler halts the
program and prints the stack trace.
Here is a sample program that creates and throws an exception. The handler that catches the
exception rethrows it to the outer handler.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
26
6 – Exception Handling




Example:
// Demonstrate throw.
class ThrowDemo {
static void demoproc() {
try
{
throw new NullPointerException("demo");
} catch(NullPointerException e) {
System.out.println("Caught inside demoproc.");
throw e; // rethrow the exception
}
}
public static void main(String args[]) {
try {
demoproc();
} catch(NullPointerException e) {
System.out.println("Recaught: " + e);
}
}
}
This program gets two chances to deal with the same error. First, main( ) sets up an exception
context and then calls demoproc( ). The demoproc( ) method then sets up another
exceptionhandling context and immediately throws a new instance of NullPointerException,
which is caught on the next line. The exception is then rethrown. Here is the resulting output:
Caught inside demoproc.
Recaught: java.lang.NullPointerException: demo
The program also illustrates how to create one of Java’s standard exception objects.
Pay close attention to this line:
throw new NullPointerException("demo");
Here, new is used to construct an instance of NullPointerException. Many of Java’s builtin runtime exceptions have at least two constructors: one with no parameter and one that takes a
string parameter. When the second form is used, the argument specifies a string that describes
the exception. This string is displayed when the object is used as an argument to print( ) or
println( ). It can also be obtained by a call to getMessage( ), which is defined by Throwable.
Explain use of throws.

If a method is capable of causing an exception that it does not handle, it must specify this
behavior so that callers of the method can guard themselves against that exception. You do this
by including a throws clause in the method’s declaration. Athrows clause lists the types of
exceptions that a method might throw. This is necessary for all exceptions, except those of type
Error or RuntimeException, or any of their subclasses. All other exceptions that a method can
throw must be declared in the throws clause. If they are not, a compile-time error will result.
This is the general form of a method declaration that includes a throws clause:
type method-name(parameter-list) throws exception-list
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
27
6 – Exception Handling
{
// body of method


}
Here, exception-list is a comma-separated list of the exceptions that a method can throw.
Following is an example of an incorrect program that tries to throw an exception that it does
not catch. Because the program does not specify a throws clause to declare this fact, the
program will not compile.
// This program contains an error and will not compile.
class ThrowsDemo {
static void throwOne() {
System.out.println("Inside throwOne.");
throw new IllegalAccessException("demo");
}
public static void main(String args[]) {
throwOne();
}
}
To make this example compile, you need to make two changes. First, you need to declare that
throwOne( ) throws IllegalAccessException. Second, main( ) must define a try/catch statement
that catches this exception.
The corrected example is shown here:
// This is now correct.
class ThrowsDemo {
static void throwOne() throws IllegalAccessException {
System.out.println("Inside throwOne.");
throw new IllegalAccessException("demo");
}
public static void main(String args[]) {
try {
throwOne();
} catch (IllegalAccessException e) {
System.out.println("Caught " + e);
}
}
}
Explain use of finally.


When exceptions are thrown, execution in a method takes a rather abrupt, nonlinear path that
alters the normal flow through the method. Depending upon how the method is coded, it is
even possible for an exception to cause the method to return prematurely. This could be a
problem in some methods.
For example, if a method opens a file upon entry and closes it upon exit, then you will not want
the code that closes the file to be bypassed by the exception-handling mechanism. The finally
keyword is designed to address this contingency.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
28
6 – Exception Handling



Finally creates a block of code that will be executed after a try/catch block has completed and
before the code following the try/catch block. The finally block will execute whether or not an
exception is thrown. If an exception is thrown, the finally block will execute even if no catch
statement matches the exception.
Any time a method is about to return to the caller from inside a try/catch block, via an uncaught
exception or an explicit return statement, the finally clause is also executed just before the
method returns.
This can be useful for closing file handles and freeing up any other resources that might have
been allocated at the beginning of a method with the intent of disposing of them before
returning. The finally clause is optional. However, each try statement requires at least one catch
or a finally clause.
Here is an example program that shows three methods that exit in various ways, none
without executing their finally clauses:
// Demonstrate finally.
class FinallyDemo {
// Through an exception out of the method.
static void procA() {
try {
System.out.println("inside procA");
throw new RuntimeException("demo");
} finally {
System.out.println("procA's finally");
}
}
// Return from within a try block.
static void procB() {
try {
System.out.println("inside procB");
return;
} finally {
System.out.println("procB's finally");
}
}
// Execute a try block normally.
static void procC() {
try {
System.out.println("inside procC");
} finally {
System.out.println("procC's finally");
}
}
public static void main(String args[]) {
try {
procA();
} catch (Exception e) {
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
29
6 – Exception Handling
System.out.println("Exception caught");
}
procB();
procC();
}

}
In this example, procA( ) prematurely breaks out of the try by throwing an exception. The finally
clause is executed on the way out. procB( )’s try statement is exited via a return statement. The
finally clause is executed before procB( ) returns. In procC( ), the try statement executes
normally, without error. However, the finally block is still executed.
Output:
inside procA
procA’s finally
Exception caught
inside procB
procB’s finally
inside procC
procC’s finally
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
30
7 – Multithreaded Programming
What is multithreading? Why it is required?



Java provides built-in support for multithreaded programming. A multithreaded program
contains two or more parts that can run concurrently. Each part of such a program is called a
thread, and each thread defines a separate path of execution. A multithreading is a specialized
form of multitasking. Multitasking threads require less overhead than multitasking processes.
I need to define another term related to threads: process: A process consists of the memory
space allocated by the operating system that can contain one or more threads. A thread cannot
exist on its own; it must be a part of a process. A process remains running until all of the nondaemon threads are done executing.
Multithreading enables you to write very efficient programs that make maximum use of the
CPU, because idle time can be kept to a minimum.
Explain the life cycle of a thread

A thread goes through various stages in its life cycle. For example, a thread is born, started,
runs, and then dies. Following diagram shows complete life cycle of a thread.

Above mentioned stages are explained here:
o New: A new thread begins its life cycle in the new state. It remains in this state until
the program starts the thread. It is also referred to as a born thread.
o Runnable: After a newly born thread is started, the thread becomes runnable. A
thread in this state is considered to be executing its task.
o Waiting: Sometimes a thread transitions to the waiting state while the thread waits
for another thread to perform a task.A thread transitions back to the runnable state
only when another thread signals the waiting thread to continue executing.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
31
7 – Multithreaded Programming
o Timed waiting: A runnable thread can enter the timed waiting state for a specified
interval of time. A thread in this state transitions back to the runnable state when
that time interval expires or when the event it is waiting for occurs.
o Terminated: A runnable thread enters the terminated state when it completes its
task or otherwise terminates.
Create Thread by Implementing Runnable Interface:






The easiest way to create a thread is to create a class that implements the Runnable interface.
To implement Runnable, a class need only implement a single method called run(), which is
declared like this:
public void run( )
You will define the code that constitutes the new thread inside run() method. It is important to
understand that run() can call other methods, use other classes, and declare variables, just like
the main thread can.
After creating a class that implements Runnable will instantiate an object of type Thread from
within that class. Thread defines several constructors. The one that we will use is shown here:
Thread(Runnable threadOb, String threadName);
Here threadOb is an instance of a class that implements the Runnable interface and the name of
the new thread is specified by threadName.
After the new thread is created, it will not start running until you call its start( ) method, which
is declared within Thread. The start( ) method is shown here:
void start( );
Example:
Here is an example that creates a new thread and starts it running:
// Create a new thread.
class NewThread implements Runnable {
Thread t;
NewThread() {
// Create a new, second thread
t = new Thread(this, "Demo Thread");
System.out.println("Child thread: " + t);
t.start(); // Start the thread
}
// This is the entry point for the second thread.
public void run() {
try {
for(int i = 5; i > 0; i--) {
System.out.println("Child Thread: " + i);
// Let the thread sleep for a while.
Thread.sleep(500);
}
} catch (InterruptedException e) {
System.out.println("Child interrupted.");
}
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
32
7 – Multithreaded Programming
System.out.println("Exiting child thread.");
}
}
class ThreadDemo {
public static void main(String args[]) {
new NewThread(); // create a new thread
try {
for(int i = 5; i > 0; i--) {
System.out.println("Main Thread: " + i);
Thread.sleep(1000);
}
} catch (InterruptedException e) {
System.out.println("Main thread interrupted.");
}
System.out.println("Main thread exiting.");
}
}
Output:
Child thread: Thread[Demo Thread,5,main]
Main Thread: 5
Child Thread: 5
Child Thread: 4
Main Thread: 4
Child Thread: 3
Child Thread: 2
Main Thread: 3
Child Thread: 1
Exiting child thread.
Main Thread: 2
Main Thread: 1
Main thread exiting.
Create Thread by Extending Thread Class:


The second way to create a thread is to create a new class that extends Thread, and then to
create an instance of that class. The extending class must override the run( ) method, which is
the entry point for the new thread. It must also call start( ) to begin execution of the new
thread.
Example:
// Create a second thread by extending Thread
class NewThread extends Thread {
NewThread() {
// Create a new, second thread
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
33
7 – Multithreaded Programming
super("Demo Thread");
System.out.println("Child thread: " + this);
start(); // Start the thread
}
// This is the entry point for the second thread.
public void run() {
try {
for(int i = 5; i > 0; i--) {
System.out.println("Child Thread: " + i);
// Let the thread sleep for a while.
Thread.sleep(500);
}
} catch (InterruptedException e) {
System.out.println("Child interrupted.");
}
System.out.println("Exiting child thread.");
}
}
class ExtendThread {
public static void main(String args[]) {
new NewThread(); // create a new thread
try {
for(int i = 5; i > 0; i--) {
System.out.println("Main Thread: " + i);
Thread.sleep(1000);
}
} catch (InterruptedException e) {
System.out.println("Main thread interrupted.");
}
System.out.println("Main thread exiting.");
}
}
Output:
Child thread: Thread[Demo Thread,5,main]
Main Thread: 5
Child Thread: 5
Child Thread: 4
Main Thread: 4
Child Thread: 3
Child Thread: 2
Main Thread: 3
Child Thread: 1
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
34
7 – Multithreaded Programming
Exiting child thread.
Main Thread: 2
Main Thread: 1
Main thread exiting.
Priority of a Thread (Thread Priority):




Each thread have a priority. Priorities are represented by a number between 1 and 10. In most
cases, thread schedular schedules the threads according to their priority (known as preemptive
scheduling). But it is not guaranteed because it depends on JVM specification that which
scheduling it chooses.
3 constants defiend in Thread class:
o public static int MIN_PRIORITY
o public static int NORM_PRIORITY
o public static int MAX_PRIORITY
Default priority of a thread is 5 (NORM_PRIORITY). The value of MIN_PRIORITY is 1 and the
value of MAX_PRIORITY is 10.
Example of priority of a Thread:
class TestMultiPriority1 extends Thread{
public void run(){
System.out.println("running thread name is:"+Thread.currentThread().getName());
System.out.println("running priority is:"+Thread.currentThread().getPriority());
}
public static void main(String args[]){
TestMultiPriority1 m1=new TestMultiPriority1();
TestMultiPriority1 m2=new TestMultiPriority1();
m1.setPriority(Thread.MIN_PRIORITY);
m2.setPriority(Thread.MAX_PRIORITY);
m1.start();
m2.start();
}
}
Why synchronization is required in multithreaded programming
and how can we implement it in program?

When two or more threads need access to a shared resource, they need some way to ensure
that the resource will be used by only one thread at a time. The process by which this
synchronization is achieved is called thread synchronization. The synchronized keyword in Java
creates a block of code referred to as a critical section. Every Java object with a critical section
of code gets a lock associated with the object. To enter a critical section, a thread needs to
obtain the corresponding object's lock.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
35
7 – Multithreaded Programming


Here, object is a reference to the object being synchronized. A synchronized block ensures that
a call to a method that is a member of object occurs only after the current thread has
successfully entered object's monitor.
Here is an example, using a synchronized block within the run( ) method:
This would produce following result:
// This program uses a synchronized block.
class Callme {
void call(String msg) {
System.out.print("[" + msg);
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
System.out.println("Interrupted");
}
System.out.println("]");
}
}
// File Name : Caller.java
class Caller implements Runnable {
String msg;
Callme target;
Thread t;
public Caller(Callme targ, String s) {
target = targ;
msg = s;
t = new Thread(this);
t.start();
}
// synchronize calls to call()
public void run() {
synchronized(target) { // synchronized block
target.call(msg);
}
}
}
// File Name : Synch.java
class Synch {
public static void main(String args[]) {
Callme target = new Callme();
Caller ob1 = new Caller(target, "Hello");
Caller ob2 = new Caller(target, "Synchronized");
Caller ob3 = new Caller(target, "World");
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
36
7 – Multithreaded Programming
// wait for threads to end
try {
ob1.t.join();
ob2.t.join();
ob3.t.join();
} catch(InterruptedException e) {
System.out.println("Interrupted");
}
}
}
Output:
[Hello]
[World]
[Synchronized]
Explain interprocess communication mechanism

To avoid polling, Java includes an elegant interprocess communication mechanism via the
wait(), notify(), and notifyAll() methods. These methods are implemented as final methods in
Object, so all classes have them. All three methods can be called only from within a
synchronized context. Although conceptually advanced from a computer science perspective,
the rules for using these methods are actuallyquite simple:
o wait() tells the calling thread to give up the monitor and go to sleep until some other
thread enters the same monitor and calls notify( ).
o notify() wakes up the first thread that called wait( ) on the same object.
o notifyAll() wakes up all the threads that called wait( ) on the same object. The highest
priority thread will run first.
These methods are declared within Object, as shown here:
final void wait( ) throws InterruptedException
final void notify( )
final void notifyAll( )
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
37
8 – IO Programming
The java.io package contains nearly every class you might ever need to perform input and output
(I/O) in Java. All these streams represent an input source and an output destination. The stream in
the java.io package supports many data such as primitives, Object, localized characters, etc.
Stream

A stream can be defined as a sequence of data. there are two kinds of Streams
o InPutStream : The InputStream is used to read data from a source.
o OutPutStream : The OutputStream is used for writing data to a destination.

Java provides strong but flexible support for I/O related to Files and networks but this tutorial
covers very basic functionality related to streams and I/O.
Byte Streams



Java byte streams are used to perform input and output of 8-bit bytes.
Though there are many classes related to byte streams but the most frequently used classes are
, FileInputStream and FileOutputStream.
Following is an example which makes use of these two classes to copy an input file into an
output file:
import java.io.*;
public class CopyFile {
public static void main(String args[]) throws IOException {
FileInputStream in = null;
FileOutputStream out = null;
try {
in = new FileInputStream("input.txt");
out = new FileOutputStream("output.txt");
int c;
while ((c = in.read()) != -1) {
out.write(c);
}
} finally {
if (in != null) {
in.close();
}
if (out != null) {
out.close();
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
38
8 – IO Programming
}
}
}
}
Character Streams





Java Byte streams are used to perform input and output of 8-bit bytes, where as Java Character
streams are used to perform input and output for 16-bit unicode.
Though there are many classes related to character streams but the most frequently used
classes are FileReader and FileWriter.
Though internally FileReader uses FileInputStream and FileWriter uses FileOutputStream but
here major difference is that FileReader reads two bytes at a time and FileWriter writes two
bytes at a time.
We can re-write above example which makes use of these two classes to copy an input file
(having unicode characters) into an output file:
Example:
import java.io.*;
public class CopyFile {
public static void main(String args[]) throws IOException {
FileReader in = null;
FileWriter out = null;
try {
in = new FileReader("input.txt");
out = new FileWriter("output.txt");
int c;
while ((c = in.read()) != -1) {
out.write(c);
}
} finally {
if (in != null) {
in.close();
}
if (out != null) {
out.close();
}
}
}
}
Standard Streams

All the programming languages provide support for standard I/O where user's program can take
input from a keyboard and then produce output on the computer screen.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
39
8 – IO Programming

If you are aware if C or C++ programming languages, then you must be aware of three standard
devices STDIN, STDOUT and STDERR. Similar way Java provides following three standard
streams.
o Standard Input: This is used to feed the data to user's program and usually a
keyboard is used as standard input stream and represented as System.in.
o Standard Output: This is used to output the data produced by the user's program
and usually a computer screen is used to standard output stream and represented as
System.out.
o Standard Error: This is used to output the error data produced by the user's program
and usually a computer screen is used to standard error stream and represented as
System.err.
Reader


The Java Reader is the base class of all Reader's in the Java IO API. Subclasses include a
BufferedReader, PushbackReader, InputStreamReader, StringReader and several others.
Here is a simple Java IO Reader example:
Reader reader = new FileReader("c:\\data\\myfile.txt");
int data = reader.read();
while(data != -1){
char dataChar = (char) data;
data = reader.read();
}

Combining Readers With InputStreams
Reader reader = new InputStreamReader(inputStream);
Writer


The Java Writer class is the base class of all Writers in the Java IO API. Subclasses include
BufferedWriter and PrintWriter among others.
Here is a simple Java IO Writer example:
Writer writer = new FileWriter("c:\\data\\file-output.txt");
writer.write("Hello World Writer");
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
40
8 – IO Programming
writer.close();

Combining Readers With InputStreams
Writer writer = new OutputStreamWriter(outputStream);
File Class


Java File class represents the files and directory pathnames in an abstract manner. This class is
used for creation of files and directories, file searching, file deletion etc.
The File object represents the actual file/directory on the disk. Below given is the list of
constructors to create a File object.
SR.NO
Methods with Description
1
File(File parent, String child)
This constructor creates a new File instance from a parent abstract pathname
and a child pathname string.
2
File(String pathname)
This constructor creates a new File instance by converting the given pathname
string into an abstract pathname.
3
File(String parent, String child)
This constructor creates a new File instance from a parent pathname string and
a child pathname string.
4
File(URI uri)
This constructor creates a new File instance by converting the given file: URI
into an abstract pathname.

Once you have File object in hand then there is a list of helper methods which can be used
manipulate the files.
SR.NO Methods with Description
1
public boolean isAbsolute()
Tests whether this abstract pathname is absolute. Returns true if this abstract
pathname is absolute, false otherwise
2
public String getAbsolutePath()
Returns the absolute pathname string of this abstract pathname.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
41
8 – IO Programming
3
public boolean canRead()
Tests whether the application can read the file denoted by this abstract
pathname. Returns true if and only if the file specified by this abstract
pathname exists and can be read by the application; false otherwise.
4
public boolean canWrite()
Tests whether the application can modify to the file denoted by this abstract
pathname. Returns true if and only if the file system actually contains a file
denoted by this abstract pathname and the application is allowed to write to
the file; false otherwise.
5
public boolean exists()
Tests whether the file or directory denoted by this abstract pathname exists.
Returns true if and only if the file or directory denoted by this abstract
pathname exists; false otherwise
6
public boolean isDirectory()
Tests whether the file denoted by this abstract pathname is a directory. Returns
true if and only if the file denoted by this abstract pathname exists and is a
directory; false otherwise.
7
public boolean isFile()
Tests whether the file denoted by this abstract pathname is a normal file. A file
is normal if it is not a directory and, in addition, satisfies other systemdependent criteria. Any non-directory file created by a Java application is
guaranteed to be a normal file. Returns true if and only if the file denoted by
this abstract pathname exists and is a normal file; false otherwise
.
8
public long lastModified()
Returns the time that the file denoted by this abstract pathname was last
modified. Returns a long value representing the time the file was last modified,
measured in milliseconds since the epoch (00:00:00 GMT, January 1, 1970).
9
public long length()
Returns the length of the file denoted by this abstract pathname. The return
value is unspecified if this pathname denotes a directory.
10
public boolean delete()
Deletes the file or directory denoted by this abstract pathname. If this
pathname denotes a directory, then the directory must be empty in order to be
deleted.
11
public String[] list()
Returns an array of strings naming the files and directories in the directory
denoted by this abstract pathname.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
42
8 – IO Programming
FileOutputStream


Java FileOutputStream is an output stream for writing data to a file.
If you have to write primitive values then use FileOutputStream.Instead, for character-oriented
data, prefer FileWriter.But you can write byte-oriented as well as character-oriented data.

Example :
import java.io.*;
class Test{
public static void main(String args[]){
try{
FileOutputstream fout=new FileOutputStream("abc.txt");
String s="Sachin Tendulkar is my favourite player";
byte b[]=s.getBytes();//converting string into byte array
fout.write(b);
fout.close();
System.out.println("success...");
}catch(Exception e)
{
system.out.println(e);
}
}
}
FileInputStream


Java FileInputStream class obtains input bytes from a file.It is used for reading streams of raw
bytes such as image data. For reading streams of characters, consider using FileReader.
It should be used to read byte-oriented data for example to read image, audio, video etc.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
43
8 – IO Programming

Example :
import java.io.*;
class SimpleRead{
public static void main(String args[]){
try{
FileInputStream fin=new FileInputStream("abc.txt");
int i=0;
while((i=fin.read())!=-1){
System.out.println((char)i);
}
fin.close();
}
catch(Exception e){
system.out.println(e);
}
}
}
InputStreamReader


The Java.io.InputStreamReader class is a bridge from byte streams to character streams.It reads
bytes and decodes them into characters using a specified charset.
Constructors:
S.N.
Constructor & Description
1
InputStreamReader(InputStream in)
This creates an InputStreamReader that uses the default charset.
2
InputStreamReader(InputStream in, Charset cs)
This creates an InputStreamReader that uses the given charset.
3
InputStreamReader(InputStream in, CharsetDecoder dec)
This creates an InputStreamReader that uses the given charset decoder.
4
InputStreamReader(InputStream in, String charsetName)
This creates an InputStreamReader that uses the named charset.

Methods:
S.N.
Method & Description
1
void close()
This method closes the stream and releases any system resources associated
with it.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
44
8 – IO Programming
2
String getEncoding()
This method returns the name of the character encoding being used by this
stream.
3
int read()
This method reads a single character.
4
int read(char[] cbuf, int offset, int length)
This method reads characters into a portion of an array.
5
boolean ready()
This method tells whether this stream is ready to be read.
OutputStreamWriter


The Java.io.OutputStreamWriter class is a bridge from character streams to byte streams.
Characters written to it are encoded into bytes using a specified charset.
Constructors:
S.N.
Constructor & Description
1
OutputStreamWriter(OutputStream out)
This creates an OutputStreamWriter that uses the default character encoding.
2
OutputStreamWriter(OutputStream out, Charset cs)
This creates an OutputStreamWriter that uses the given charset.
3
OutputStreamWriter(OutputStream out, CharsetEncoder enc)
This creates an OutputStreamWriter that uses the given charset encoder.
4
OutputStreamWriter(OutputStream out, String charsetName)
This creates an OutputStreamWriter that uses the named charset.

Methods:
S.N.
Method & Description
1
void close()
This method closes the stream, flushing it first.
2
void flush()
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
45
8 – IO Programming
This method flushes the stream.
3
String getEncoding()
This method returns the name of the character encoding being used by this
stream.
4
void write(char[] cbuf, int off, int len)
This method writes a portion of an array of characters.
5
void write(int c)
This method writes a single character.
6
void write(String str, int off, int len)
This method writes a portion of a string.
FileReader



This class inherits from the InputStreamReader class. FileReader is used for reading streams of
characters.
This class has several constructors to create required objects. Below given are the list of
constructors provided by the FileReader class.
Contractors:
SR.NO
Constructors and Description
1
FileReader(File file)
This constructor creates a new FileReader, given the File to read
from.
2
FileReader(FileDescriptor fd)
This constructor creates a new FileReader, given the FileDescriptor to
read from.
3
FileReader(String fileName)
This constructor creates a new FileReader, given the name of the file
to read from.

Methods:
SR.NO
Methods with Description
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
46
8 – IO Programming
1
public int read() throws IOException
Reads a single character. Returns an int, which represents the character read.
2
public int read(char [] c, int offset, int len)
Reads characters into an array. Returns the number of characters read.

Example:
import java.io.*;
public class FileRead{
public static void main(String args[])throws IOException{
File file = new File("Hello1.txt");
// creates the file
file.createNewFile();
// creates a FileWriter Object
FileWriter writer = new FileWriter(file);
// Writes the content to the file
writer.write("This\n is\n an\n example\n");
writer.flush();
writer.close();
//Creates a FileReader Object
FileReader fr = new FileReader(file);
char [] a = new char[50];
fr.read(a); // reads the content to the array
for(char c : a)
System.out.print(c); //prints the characters one by one
fr.close();
}
}
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
47
8 – IO Programming
FileWriter



This class inherits from the OutputStreamWriter class. The class is used for writing streams of
characters.
This class has several constructors to create required objects. Below given is the list of them
Contractors:
SR.NO
Constructors and Description
1
FileWriter(File file)
This constructor creates a FileWriter object given a File object.
2
FileWriter(File file, boolean append)
This constructor creates a FileWriter object given a File object. with a
boolean indicating whether or not to append the data written.
3
FileWriter(FileDescriptor fd)
This constructor creates a FileWriter object associated with the given
file descriptor.
4
FileWriter(String fileName)
This constructor creates a FileWriter object, given a file name.
5
FileWriter(String fileName, boolean append)
This constructor creates a FileWriter object given a file name with a
boolean indicating whether or not to append the data written.

Methods:
SN
Methods with Description
1
public void write(int c) throws IOException
Writes a single character.
2
public void write(char [] c, int offset, int len)
Writes a portion of an array of characters starting from offset and with a length of
len.
3
public void write(String s, int offset, int len)
Write a portion of a String starting from offset and with a length of len.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
48
8 – IO Programming
BufferedReader


The Java.io.BufferedReader class reads text from a character-input stream, buffering characters
so as to provide for the efficient reading of characters, arrays, and lines.Following are the
important points about BufferedReader:
o The buffer size may be specified, or the default size may be used.
o Each read request made of a Reader causes a corresponding read request to be made of
the underlying character or byte stream.
Constructors:
S.N.
Constructor & Description
1
BufferedReader(Reader in)
This creates a buffering character-input stream that uses a default-sized
input buffer.
2
BufferedReader(Reader in, int sz)
This creates a buffering character-input stream that uses an input buffer of
the specified size.

Methods:
S.N.
Method & Description
1
void close()
This method closes the stream and releases any system resources associated
with it.
2
int read()
This method reads a single character.
3
int read(char[] cbuf, int off, int len)
This method reads characters into a portion of an array.
4
String readLine()
This method reads a line of text.
5
void reset()
This method resets the stream.
6
long skip(long n)
This method skips characters.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
49
8 – IO Programming
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
50
9 – Collection Classes
List Interface.


The List interface extends Collection and declares the behavior of a collection that stores a
sequence of elements.
o Elements can be inserted or accessed by their position in the list, using a zero-based
index.
o A list may contain duplicate elements.
o In addition to the methods defined by Collection, List defines some of its own, which
are summarized in the following below Table.
o Several of the list methods will throw an UnsupportedOperationException if the
collection cannot be modified, and a ClassCastException is generated when one
object is incompatible with another.
Methods :
SN
Methods with Description
1
void add(int index, Object obj)
Inserts obj into the invoking list at the index passed in index. Any pre-existing
elements at or beyond the point of insertion are shifted up. Thus, no elements are
overwritten.
2
boolean addAll(int index, Collection c)
Inserts all elements of c into the invoking list at the index passed in index. Any preexisting elements at or beyond the point of insertion are shifted up. Thus, no elements
are overwritten. Returns true if the invoking list changes and returns false otherwise.
3
Object get(int index)
Returns the object stored at the specified index within the invoking collection.
4
int indexOf(Object obj)
Returns the index of the first instance of obj in the invoking list. If obj is not an
element of the list, .1 is returned.
5
int lastIndexOf(Object obj)
Returns the index of the last instance of obj in the invoking list. If obj is not an element
of the list, .1 is returned.
6
ListIterator listIterator( )
Returns an iterator to the start of the invoking list.
7
ListIterator listIterator(int index)
Returns an iterator to the invoking list that begins at the specified index.
8
Object remove(int index)
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
51
9 – Collection Classes
Removes the element at position index from the invoking list and returns the deleted
element. The resulting list is compacted. That is, the indexes of subsequent elements
are decremented by one
9
Object set(int index, Object obj)
Assigns obj to the location specified by index within the invoking list.
10
List subList(int start, int end)
Returns a list that includes elements from start to end.1 in the invoking list. Elements
in the returned list are also referenced by the invoking object.

A sample of a List is given below:
import java.util.*;
public class CollectionsDemo {
public static void main(String[] args) {
List a1 = new ArrayList();
a1.add("Zara");
a1.add("Mahnaz");
a1.add("Ayan");
System.out.println(" ArrayList Elements");
System.out.print("\t" + a1);
List l1 = new LinkedList();
l1.add("Zara");
l1.add("Mahnaz");
l1.add("Ayan");
System.out.println();
System.out.println(" LinkedList Elements");
System.out.print("\t" + l1);
}
}
ArrayList Class.

The java.util.ArrayList class provides resizable-array and implements the List interface.Following
are the important points about ArrayList:
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
52
9 – Collection Classes

o It implements all optional list operations and it also permits all elements, includes
null.
o It provides methods to manipulate the size of the array that is used internally to
store the list.
o The constant factor is low compared to that for the LinkedList implementation.
Constructors:
S.N.
Constructor & Description
1
ArrayList()
This constructor is used to create an empty list with an initial capacity sufficient to
hold 10 elements.
2
ArrayList(Collection<? extends E> c)
This constructor is used to create a list containing the elements of the specified
collection.
3
ArrayList(int initialCapacity)
This constructor is used to create an empty list with an initial capacity.

Methods:
S.N.
Method & Description
1
void add(int index, E element)
This method inserts the specified element at the specified position in this list.
2
boolean addAll(Collection<? extends E> c)
This method appends all of the elements in the specified collection to the end of this
list, in the order that they are returned by the specified collection's Iterator
3
void clear()
This method removes all of the elements from this list.
4
boolean contains(Object o)
This method returns true if this list contains the specified element.
5
E get(int index)
This method returns the element at the specified position in this list.
6
int indexOf(Object o)
This method returns the index of the first occurrence of the specified element in this
list, or -1 if this list does not contain the element.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
53
9 – Collection Classes
7
boolean isEmpty()
This method returns true if this list contains no elements.
8
int lastIndexOf(Object o)
This method returns the index of the last occurrence of the specified element in this
list, or -1 if this list does not contain the element.
9
boolean remove(Object o)
This method removes the first occurrence of the specified element from this list, if it is
present.
10
E set(int index, E element)
This method replaces the element at the specified position in this list with the specified
element.
11
int size()
This method returns the number of elements in this list.
12
Object[] toArray()
This method returns an array containing all of the elements in this list in proper
sequence (from first to last element).
LinkedList Class.


The LinkedList class extends AbstractSequentialList and implements the List interface. It
provides a linked-list data structure.
Constructors:
SN
Constructors and Description
1
LinkedList( )
This constructor builds an empty linked list.
2
LnkedList(Collection c)
This constructor builds a linked list that is initialized with the elements of the collection
c.

Methods:
SN
Methods with Description
1
void add(int index, Object element)
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
54
9 – Collection Classes
Inserts the specified element at the specified position index in this list. Throws
IndexOutOfBoundsException if the specified index is is out of range (index < 0 || index >
size()).
2
boolean addAll(Collection c)
Appends all of the elements in the specified collection to the end of this list, in the order
that
they
are
returned
by
the
specified
collection's
iterator.
Throws
NullPointerException if the specified collection is null
3
void addFirst(Object o)
Inserts the given element at the beginning of this list.
4
void addLast(Object o)
Appends the given element to the end of this list.
5
void clear()
Removes all of the elements from this list.
6
boolean contains(Object o)
Returns true if this list contains the specified element. More formally, returns true if and
only if this list contains at least one element e such that (o==null ? e==null : o.equals(e)).
7
Object get(int index)
Returns
the
element
at
the
specified
position
in
this
list.
Throws
IndexOutOfBoundsException if the specified index is is out of range (index < 0 || index
>= size()).
8
Object getFirst()
Returns the first element in this list. Throws NoSuchElementException if this list is
empty.
9
Object getLast()
Returns the last element in this list. Throws NoSuchElementException if this list is
empty.
10
int indexOf(Object o)
Returns the index in this list of the first occurrence of the specified element, or -1 if the
List does not contain this element.
11
int lastIndexOf(Object o)
Returns the index in this list of the last occurrence of the specified element, or -1 if the
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
55
9 – Collection Classes
list does not contain this element.
12
Object remove(int index)
Removes
the
element
at
the
specified
position
in
this
list.
Throws
NoSuchElementException if this list is empty.
13
boolean remove(Object o)
Removes the first occurrence of the specified element in this list. Throws
NoSuchElementException if this list is empty. Throws IndexOutOfBoundsException if the
specified index is is out of range (index < 0 || index >= size()).
14
Object removeFirst()
Removes and returns the first element from this list. Throws NoSuchElementException if
this list is empty.
15
Object removeLast()
Removes and returns the last element from this list. Throws NoSuchElementException if
this list is empty.
16
Object set(int index, Object element)
Replaces the element at the specified position in this list with the specified element.
Throws IndexOutOfBoundsException if the specified index is is out of range (index < 0 ||
index >= size()).
17
int size()
Returns the number of elements in this list.
18
Object[] toArray()
Returns an array containing all of the elements in this list in the correct order. Throws
NullPointerException if the specified array is null.

Example :
import java.util.*;
public class LinkedListDemo {
public static void main(String args[]) {
// create a linked list
LinkedList ll = new LinkedList();
// add elements to the linked list
ll.add("F");
ll.add("B");
ll.add("D");
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
56
9 – Collection Classes
ll.add("E");
ll.add("C");
ll.addLast("Z");
ll.addFirst("A");
ll.add(1, "A2");
System.out.println("Original contents of ll: " + ll);
// remove elements from the linked list
ll.remove("F");
ll.remove(2);
System.out.println("Contents of ll after deletion: "
+ ll);
// remove first and last elements
ll.removeFirst();
ll.removeLast();
System.out.println("ll after deleting first and last: "
+ ll);
// get and set a value
Object val = ll.get(2);
ll.set(2, (String) val + " Changed");
System.out.println("ll after change: " + ll);
}
}
Enumeration Interface.



The Enumeration interface defines the methods by which you can enumerate (obtain one at a
time) the elements in a collection of objects.
This legacy interface has been superceded by Iterator. Although not deprecated, Enumeration is
considered obsolete for new code. However, it is used by several methods defined by the legacy
classes such as Vector and Properties, is used by several other API classes, and is currently in
widespread use in application code.
The methods declared by Enumeration are summarized in the following table:
SN
Methods with Description
1
boolean hasMoreElements( )
When implemented, it must return true while there are still more elements to
extract, and false when all the elements have been enumerated.
2
Object nextElement( )
This returns the next object in the enumeration as a generic Object reference.

Example:
import java.util.Vector;
import java.util.Enumeration;
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
57
9 – Collection Classes
public class EnumerationTester {
public static void main(String args[]) {
Enumeration days;
Vector dayNames = new Vector();
dayNames.add("Sunday");
dayNames.add("Monday");
dayNames.add("Tuesday");
dayNames.add("Wednesday");
dayNames.add("Thursday");
dayNames.add("Friday");
dayNames.add("Saturday");
days = dayNames.elements();
while (days.hasMoreElements()){
System.out.println(days.nextElement());
}
}
}
Vector Class.



Vector implements a dynamic array. It is similar to ArrayList, but with two differences:
o Vector is synchronized.
o Vector contains many legacy methods that are not part of the collections framework.
Vector proves to be very useful if you don't know the size of the array in advance or you just
need one that can change sizes over the lifetime of a program.
Constructors :
SR.NO
Constructor and Description
1
Vector( )
This constructor creates a default vector, which has an initial size of 10
2
Vector(int size)
This constructor accepts an argument that equals to the required size, and
creates a vector whose initial capacity is specified by size:
3
Vector(int size, int incr)
This constructor creates a vector whose initial capacity is specified by size and
whose increment is specified by incr. The increment specifies the number of
elements to allocate each time that a vector is resized upward
4
Vector(Collection c)
creates a vector that contains the elements of collection c

Methods
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
58
9 – Collection Classes
SN
Methods with Description
1
void add(int index, Object element)
Inserts the specified element at the specified position in this Vector.
2
boolean addAll(Collection c)
Appends all of the elements in the specified Collection to the end of this Vector,
in the order that they are returned by the specified Collection's Iterator.
3
void addElement(Object obj)
Adds the specified component to the end of this vector, increasing its size by
one.
4
int capacity()
Returns the current capacity of this vector.
5
void clear()
Removes all of the elements from this Vector.
6
boolean contains(Object elem)
Tests if the specified object is a component in this vector.
7
boolean containsAll(Collection c)
Returns true if this Vector contains all of the elements in the specified
Collection.
8
Enumeration elements()
Returns an enumeration of the components of this vector.
9
Object firstElement()
Returns the first component (the item at index 0) of this vector.
10
Object get(int index)
Returns the element at the specified position in this Vector.
11
int indexOf(Object elem)
Searches for the first occurence of the given argument, testing for equality
using the equals method.
12
boolean isEmpty()
Tests if this vector has no components.
13
Object lastElement()
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
59
9 – Collection Classes
Returns the last component of the vector.
14
int lastIndexOf(Object elem)
Returns the index of the last occurrence of the specified object in this vector.
15
Object remove(int index)
Removes the element at the specified position in this Vector.
16
boolean removeAll(Collection c)
Removes from this Vector all of its elements that are contained in the specified
Collection.
17
Object set(int index, Object element)
Replaces the element at the specified position in this Vector with the specified
element.
18
int size()
Returns the number of components in this vector.

Example:
import java.util.*;
public class VectorDemo {
public static void main(String args[]) {
// initial size is 3, increment is 2
Vector v = new Vector(3, 2);
System.out.println("Initial size: " + v.size());
System.out.println("Initial capacity: " +
v.capacity());
v.addElement(new Integer(1));
System.out.println("Capacity after additions: " +
v.capacity());
System.out.println("First element: " +
(Integer)v.firstElement());
System.out.println("Last element: " +
(Integer)v.lastElement());
if(v.contains(new Integer(3)))
System.out.println("Vector contains 3.");
// enumerate the elements in the vector.
Enumeration vEnum = v.elements();
System.out.println("\nElements in vector:");
while(vEnum.hasMoreElements())
System.out.print(vEnum.nextElement() + " ");
System.out.println();
}
}
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
60
9 – Collection Classes
Properties Class.




Properties is a subclass of Hashtable. It is used to maintain lists of values in which the key is a
String and the value is also a String.
The Properties class is used by many other Java classes. For example, it is the type of object
returned by System.getProperties( ) when obtaining environmental values.
Properties define the following instance variable. This variable holds a default property list
associated with a Properties object.
Constructors:
SR.No Constructors and Description

1
Properties( )
This constructor creates a Properties object that has no default values
2
Properties(Properties propDefault)
creates an object that uses propDefault for its default values. In both cases, the
property list is empty
Methods :
SN Methods with Description
1
String getProperty(String key)
Returns the value associated with key. A null object is returned if key is neither in the
list nor in the default property list.
2
String getProperty(String key, String defaultProperty)
Returns the value associated with key. defaultProperty is returned if key is neither in
the list nor in the default property list.
3
void list(PrintStream streamOut)
Sends the property list to the output stream linked to streamOut.
4
void list(PrintWriter streamOut)
Sends the property list to the output stream linked to streamOut.
5
void load(InputStream streamIn) throws IOException
Inputs a property list from the input stream linked to streamIn.
6
Enumeration propertyNames( )
Returns an enumeration of the keys. This includes those keys found in the default
property list, too.
7
Object setProperty(String key, String value)
Associates value with key. Returns the previous value associated with key, or returns
null if no such association exists
8
void store(OutputStream streamOut, String description)
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
61
9 – Collection Classes
After writing the string specified by description, the property list is written to the
output stream linked to streamOut

Example :
import java.util.*;
public class PropDemo {
public static void main(String args[]) {
Properties capitals = new Properties();
Set states;
String str;
capitals.put("Illinois", "Springfield");
capitals.put("Missouri", "Jefferson City");
capitals.put("Washington", "Olympia");
capitals.put("California", "Sacramento");
capitals.put("Indiana", "Indianapolis");
// Show all states and capitals in hashtable.
states = capitals.keySet(); // get set-view of keys
Iterator itr = states.iterator();
while(itr.hasNext()) {
str = (String) itr.next();
System.out.println("The capital of " +
str + " is " + capitals.getProperty(str) + ".");
}
System.out.println();
// look for state not in list -- specify default
str = capitals.getProperty("Florida", "Not Found");
System.out.println("The capital of Florida is "
+ str + ".");
}
}
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
62
10 – Networking with java.net
InetAddress class


Java InetAddress class represents an IP address. The java.net.InetAddress class provides
methods to get the IP of any host name for example www.gtu.ac.in, www.google.com,
www.facebook.com etc.
Methods :
SN
Methods with Description
1
public static InetAddress getByName(String host) throws UnknownHostException
it returns the instance of InetAddress containing LocalHost IP and name.
2
public static InetAddress getLocalHost() throws UnknownHostException
it returns the instance of InetAdddress containing local host name and address.
3
public String getHostName()
it returns the host name of the IP address.
4
public String getHostAddress()
it returns the IP address in string format.

A sample of a List is given below:
import java.io.*;
import java.net.*;
public class InetDemo{
public static void main(String[] args)
{
try{
InetAddress ip=InetAddress.getByName("www.javatpoint.com");
System.out.println("Host Name: "+ip.getHostName());
System.out.println("IP Address: "+ip.getHostAddress());
}
catch(Exception e)
{
System.out.println(e);
}
}
}
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
63
10 – Networking with java.net
Socket Class.



This class implements client sockets (also called just "sockets"). A socket is an endpoint for
communication between two machines.
The actual work of the socket is performed by an instance of the SocketImpl class. An
application, by changing the socket factory that creates the socket implementation, can
configure itself to create sockets appropriate to the local firewall.
Constructors:
S.N.
Constructor & Description
1
Socket()
Creates an unconnected socket, with the system-default type of SocketImpl.
2
Socket(InetAddress address, int port)
Creates a stream socket and connects it to the specified port number at the specified
IP address.

Methods:
S.N.
Method & Description
1
close()
Closes this socket.
2
connect(SocketAddress endpoint)
Connects this socket to the server.
3
getInetAddress()
Returns the address to which the socket is connected.
4
getPort()
Returns the remote port number to which this socket is connected.
5
isConnected()
Returns the connection state of the socket.
6
getInputStream()
returns the InputStream attached with this socket.
7
getOutputStream()
returns the OutputStream attached with this socket.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
64
10 – Networking with java.net
ServerSocket Class.



This class implements server sockets. A server socket waits for requests to come in over the
network. It performs some operation based on that request, and then possibly returns a result
to the requester.
The actual work of the server socket is performed by an instance of the SocketImpl class. An
application can change the socket factory that creates the socket implementation to configure
itself to create sockets appropriate to the local firewall.
Constructors:
SN
Constructors and Description
1
ServerSocket()
This constructor builds an empty linked list.
2
ServerSocket(int port)
Creates a server socket, bound to the specified port.

Methods:
SN
Methods with Description
1
accept()
Listens for a connection to be made to this socket and accepts it.
2
close()
Closes this socket.
3
getInetAddress()
Returns the local address of this server socket.
Example of Java Socket Programming

File: MyServer.java
import java.io.*;
import java.net.*;
public class MyServer {
public static void main(String[] args){
try{
ServerSocket ss=new ServerSocket(6666);
Socket s=ss.accept();//establishes connection
DataInputStream dis=new DataInputStream(s.getInputStream());
String str=(String)dis.readUTF();
System.out.println("message= "+str);
ss.close();
}
catch(Exception e)
{
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
65
10 – Networking with java.net
System.out.println(e);
}
}
}

File: MyClient.java
import java.io.*;
import java.net.*;
public class MyClient {
public static void main(String[] args)
{
try
{
Socket s=new Socket("localhost",6666);
DataOutputStream dout=new DataOutputStream(s.getOutputStream());
dout.writeUTF("Hello Server");
dout.flush();
dout.close();
s.close();
}
catch(Exception e)
{
System.out.println(e);
}
}
}
DatagramSocket Class & DatagramPacket Class




DatagramSocket :
Java DatagramSocket class represents a connection-less socket for sending and receiving
datagram packets.
A datagram is basically an information but there is no guarantee of its content, arrival or arrival
time.
The Commonly Used Constructors of DatagramSocket:
SN
Methods with Description
1
DatagramSocket()
it creates a datagram socket and binds it with the available Port Number on the
localhost machine.
2
DatagramSocket(int port)
it creates a datagram socket and binds it with the given Port Number.
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
66
10 – Networking with java.net

The Commonly Used Methods of Datagram Socket:
SN
Methods with Description
1
send(DatagramPacket p)
Sends a datagram packet from this socket.
2
receive(DatagramPacket p)
Receives a datagram packet from this socket.



DatagramPacket:
Java DatagramPacket is a message that can be sent or received. If you send multiple packet, it
may arrive in any order. Additionally, packet delivery is not guaranteed.
The Commonly Used Constructors of DatagramPacket:
SN
Methods with Description
1
DatagramPacket(byte[] barr, int length)
it creates a datagram packet. This constructor is used to receive the packets.
2
DatagramPacket(byte[] barr, int length, InetAddress address, int port)
it creates a datagram packet. This constructor is used to send the packets.

Example of Sending DatagramPacket by DatagramSocket:
//DSender.java
import java.net.*;
public class DSender{
public static void main(String[] args) throws Exception {
DatagramSocket ds = new DatagramSocket();
String str = "Welcome java";
InetAddress ip = InetAddress.getByName("127.0.0.1");
DatagramPacket dp = new DatagramPacket(str.getBytes(), str.length(), ip, 3000);
ds.send(dp);
ds.close();
}
}
//DReceiver.java
import java.net.*;
public class DReceiver{
public static void main(String[] args) throws Exception {
DatagramSocket ds = new DatagramSocket(3000);
byte[] buf = new byte[1024];
DatagramPacket dp = new DatagramPacket(buf, 1024);
ds.receive(dp);
String str = new String(dp.getData(), 0, dp.getLength());
System.out.println(str);
ds.close();
}
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
67
10 – Networking with java.net
}
Prof. Arjun Bala, CE Department | 2150704 – Object Oriented Programming with Java
68
11 – Introduction to Object orientation
Introduction to Object orientation

Object-oriented modeling and design is a way of thinking about problems using models
organized around real-world concepts.
 The fundamental construct is object, which combine data structure and behavior.
 Object-Oriented Models are useful for
i. Understanding problems
ii. Communicating with application experts
iii. Modeling enterprises
iv. Preparing documentation
v. Designing programs and databases
 The subject is not primarily about OO-language or coding.
 It emphasize on initial stages of process development i.e. Requirement Gathering, planning etc.
Object-oriented analysis and design (OOAD) is a software engineering approach that models a
system as a group of interacting objects.
Explain Object Orientation in detail.

Object-oriented (OO) means that we organize software as a collection of isolated objects that
incorporate both data structure and behavior.
 Object Orientation is about viewing and modeling the world/system as a set of interacting and
interrelated objects.
 Characteristics of OO approach include four aspects: identity, classification, inheritance and
polymorphism.
i. Identity
 Identity means data is quantized into discrete and distinguishable entities. Each object is having
its own inherent identity.
e.g. identity of Pen object is very different with an identity of Table object
 Objects are distinct even if all their attribute values (i.e. name and size) are identical. In
programming language each object has unique handle by which it can be referenced.
 Objects can be concrete (real/existing), such as a file in a file system, or conceptual, such as a
scheduling policy in a multiprocessing operating system.
 Language implements the handle in various ways, such as an address, array index, etc.
ii. Classification
 Abstract entities with the same structure (attributes) and behavior (operations) are grouped
into classes. Example: Paragraph, Chess Piece etc.
 A class is an abstraction that describes properties important to an application and ignores the
rest.
 Each class describes a possibly infinite set of individual objects.
 Each object is said to be an instance of its class.
 An object has its own value for each attribute but shares the attribute names and operations
with other instances of the class.
 Choice of class is arbitrary and depends on application.
 Each class describe infinite set of individual object and each object is instance of class.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
69
11 – Introduction to Object orientation
iii. Inheritance
 Sharing of attributes and operations based on a hierarchical relationship. Each subclass inherits
all features of super class and adds its unique features.
 A super class has general information that subclasses refine and elaborate. Each subclass
incorporates, or inherits all the features of its super class and adds its own unique features.
 Subclasses need not repeat the features of the super class.
Example, Scrolling Window, and Fixed Window are subclasses of Window.
 The ability to factor out common features of several classes into a super class can greatly
reduce repetition within designs and programs and is one of the main.
Figure : Inheritance
iv. Polymorphism
 Polymorphism means that the same operation may behave differently for different classes.
Example, the move operation behaves differently for a pawn than for the queen in a chess
game.
 Polymorphism- a Greek term means ability to take more than one form.
 The same operation may behave differently on different classes
 An operation is a procedure or transformation that an object performs or is subject to.
 An implementation of an operation by a specific class is called a method.
 An Operation is a procedure or transformation that an object performs.
 Implementation of operation by a specific class is called method.
Modeling as a Design Technique and modeling concepts
Abstraction
 Abstraction is fundamental human capability that permits us to deal with complexity.
 A process allowing focusing on most important aspects while ignoring less important details.
Abstraction is the selective examination of certain aspects of a problem.
 The goal of abstraction is to isolate those aspects that are important for some purpose and
suppress those aspects that are unimportant.
 Abstraction determines what is, and is not, important.
 The purpose of an abstraction is to limit the universe so we can understand. A good model
captures the crucial aspects of a problem and omits the others.
 In building model we must not search for absolute truth but for adequacy.
 There is no single “correct” model, only adequate and inadequate ones.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
70
11 – Introduction to Object orientation
Property of Abstraction: All the abstraction are incomplete and inaccurate.
 No Abstraction is perfect.
E.g. All human words and language are abstractions (incomplete description of real world).
 No single model is sufficient to represent any situation.
 Abstraction does not destroy usefulness of a system.
 The purpose is to limit the universe which eliminates the complexity.
 Software model that contains extra detail unnecessarily limits choice of design decisions and
diverts from the real issues.
Explain Three models
Class Model
 The structure of an object in system includes:
i. Identity
ii. Relationship to other object
iii. Attributes
iv. Operations
 This model provides context for state and interaction model.
 The goal in constructing class model is to capture those concepts from real world that are
important to application.
State Model
 Describes history and behavior of a system with respect to time.
 Explains context of events and organization of events with states.
 Actions and events in state model become operations on object in class model.
Interaction Model
 Explains interactions between objects.
 It also explains, how individual object collaborate to achieve behavior of system as a whole.
i. Use Case Model: Document major theme for interactions between system and outside
actors.
ii. Sequence Model: Describes object that interact and time sequence of their interactions.
iii. Activity Model: shows flow of control among processing steps of a computation.
Relationship among the Models
 Each model describes one aspect of the system but contains references to the other models,
The class model describes data structure on which the state and interaction models operate.
 The operations in the class model correspond to events and actions. The state model describes
the control structure of objects. It shows decision that depends on object values causes actions
that change object values and state. The interaction models focuses on the exchanges between
objects and provide a complete overview of the operation of a system.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
71
12 – Class Modeling
Class Modeling





A class modeling captures static structure of a system by characterizing the objects in the
system, the relationships between the objects, and the attributes and operations for each class
of objects.
Class model is most important among three models.
Emphasizes on building a system around objects rather than functionality.
Class Model closely corresponds to the real world and is consequently more flexible with
respect to the change.
The purpose of class modeling is to describe object.
Object and Class Concepts
Object:
 Object is a concept, abstraction, or a thing with identity that has meaning for an application
E.g. Two apples each have identity and are distinguishable.
 Objects are instances of classes.
 It often appears as a proper nouns or specific references in problem descriptions
 Some objects have real world counterparts (name of a person/company).
 While some object have conceptual entity (formula for solving quadratic equation).
 Choice of object depends on judgment and the nature of a problem. There can be many correct
representations. All Object have identity and distinguishable.
 Identity means objects are distinguished by their inherent existence and not by descriptive
properties.
 Real-world objects share two characteristics: They all have attributes and behavior.
Class:
 Class describes a group of objects with the same properties (attributes), behaviour (operations),
kinds of relationship, and Semantics. (E.g.: Person, Company, Process and Window).
 A software unit that implements one or more interfaces.
 Classes often appear as common noun and noun phrase in problem description.
 By grouping objects into class, we abstract a problem.
Class Diagram
 Class Diagram provides a Graphical notation for modeling classes and their relationships,
thereby describing possible objects.
 The most widely used diagram of UML.
 Models the static design view of a system.
 Useful in modeling business objects.
 Used to specify the structure, interfaces and relationships between classes that underlie the
system architecture.
 Primary diagram for generating codes from UML models.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
72
12 – Class Modeling
Class Diagram Notations
Sr.
No.
Name
1
Class
2
Object
3
Link
4
Association
5
Multiplicity
Symbol
Meaning
Class is an entity
of
the
class
diagram.
It
describes a group
of objects with
same properties
& behavior.
An object is an
instance
or
occurrence of a
class.
A link is a physical
or
conceptual
connection
among objects.
Ex. 1
to
1
*
*
1
6
Association
class
1
to
to
to
to
*
*
1
0….2
An association is
a description of a
links
with
common
structure
&
common
semantics.
Multiplicity
specifies
the
number
of
instances of one
class that may
relate to a single
instance of an
associated class.
It is a constraint
on the Cardinlity
of a set.
It
is
an
association that is
a class which
describes
the association
with attributes.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
73
12 – Class Modeling
7
cardinality
It describes the
count
of
elements
from
collection.
8
ordering
9
bag
10
sequence
11
qualified
association
12
generalization
It is used to
indicate
an
ordered set of
objects with no
duplication
allowed.
A bag is a
collection
of
unordered
elements with
Duplicates
allowed.
A sequence is an
ordered
collection
of
elements
with
duplicates
allowed.
Qualification
increases
the
precision of a
model.
It is used to avoid
many to many
multiplicities and
it converts into
one
to
one
multiplicity.
Generalization
organizes classes
by
their
superclass
and
sub-class
relationship.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
74
12 – Class Modeling
13
Enumeration
An enumeration
is a data type that
has a finite set
of values.
14
Aggregation
It is a strong form
of association in
which
an
aggregate object
is
made
of
constituent parts.
15
Composition
16
Abstract class
It is a form of
aggregation.
Composition
implies
ownership of the
parts by the
whole.
It is a class that
has no direct
instances.
17
Concrete class
It is a class that is
intangible; it can
have
direct
instances. Class-2
is example of
concrete class
18
package
A package is a
group
of
elements
with
common theme.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
75
12 – Class Modeling
Examples:
Class Diagram for Library Management System
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
76
12 – Class Modeling
Class Diagram for ATM
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
77
12 – Class Modeling
Class Diagram for Online Restaurant System
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
78
12 – Class Modeling
Class Diagram for Online Reservation System
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
79
12 – Class Modeling
Class Diagram for Online Shopping System
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
80
12 – Class Modeling
Purpose of class diagram
 Analysis and design of the static view of an application
 Describes responsibilities of a system.
 Base for component and deployment diagrams.
Link and Association




Link and Association are the means for establishing relationship among objects and classes.
Link and Association often appears as verbs in problem statement.
Link is a physical / conceptual connection among objects most links relate two objects, but
some links relate three or more object. It is an instance of association as shown in figure below.
Association is a description of a group of links with common structure and common semantics
as in the class diagram shown in figure below.
Figure: Many-to-many Association






Associations are indirectly bidirectional.
Both the direction of traversal is equally meaningful.
It is the only name of the association that establishes the direction.
Developers often implements associations in programming language as a references from one
object to another.
Associations are important, precisely because they break encapsulation.
Associations cannot be private to a class, because they go beyond classes.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
81
12 – Class Modeling
Figure: Association Vs. Link
Generalization and Inheritance








Generalization is the relationship between a class (the super class) and one or more variations
of the class (sub class).
Super class holds the common attributes, operations and associations. Subclass adds specific
attributes.
Each subclass inherits features of super class Ancestor and descendents.
Use of Generalization serves three purposes:
i. Support for polymorphism. (call at super class level automatically resolved)
ii. Second purpose is to structure the description of objects. (a taxonomy is formed)
iii. Third purpose is to enable reuse of code.
The terms generalization, specialization and inheritance all refer to aspects of the same idea.
Generalization: derives from the fact that the sub class generalizes to super class
Specialization: refers to the fact that the subclasses refine or specialize the super-class.
Inheritance: Is the mechanism for sharing attributes, operations, and associations via
generalization specialization relationship which is useful for parent child relationship.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
82
13 – Advanced Class Modeling
Advance class Modeling
Advance object and class concepts and Association Ends.



Association end is a connection between the line depicting an association and the icon depicting
the connected classifier.
Name of the association end may be placed near the end of the line. The association end name
is commonly referred to as role name (but it is not defined as such in the UML 2.4 standard).
The role name is optional and suppressible.
Professor "playing the role" of author is associated
with textbook end typed as Book.







- The idea of the role is that the same classifier can play the same or different roles in other
associations.
- For example, Professor could be an author of some Books or an editor.
Association end could be owned either by end classifier, or association itself
Association ends of associations with more than two ends must be owned by the association.
Ownership of association ends by an associated classifier may be indicated graphically by
a small filled circle (aka dot).
The dot is drawn at the point where line meets the classifier.
It could be interpreted as showing that the model includes a property of the type represented
by the classifier touched by the dot.
This property is owned by the classifier at the other end.
Association end query is owned by classifier QueryBuilder
and association end qbuilder is owned by association Builds itself

The "ownership" dot may be used in combination with the other graphic line-path notations for
properties of associations and association ends. These include aggregation type and
navigability.
N-ary associations/ Ternary Association



N-ary association means associations among three or more classes.
A ternary association is an association with three roles that cannot be restated as binary
associations.
The notation for a ternary association is a large diamond; each associated class connects to a
vertex of the diamond with a line.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
83
13 – Advanced Class Modeling










The above figure represents another example of Ternary Association.
You should try to avoid n-ary associations.
Normally it is decomposed into binary associations with possible qualifiers and attributes.
Many relationships involve just two things and can be modeled with the simple binary
association.
It is not however uncommon for three or more things to be involved in a relationship.
An n-ary association can be used in these circumstances and allows any or "n" number of things
to be related in a single cohesive group.
An n-ary association is used when the three or more things are all related to each other in a
structural or behavioral way.
It does not replace the use of two binary associations where a classifier is related to two other
classifiers, but the latter two classifiers aren't related to each other.
In below Figure a professor teaches a listed course for a semester.
The delivered course may use many textbooks; the same textbook may be used for multiple
delivered courses.
Aggregation and Composition
Aggregation



Aggregation is a strong form of association in which an aggregate object is made of constituent
parts.
An aggregation as relating an assembly class to one constituent part class. An assembly with
many kinds of constituent parts corresponds to many aggregations.
Aggregation is a special form of association.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
84
13 – Advanced Class Modeling





If two objects are tightly bound by a part-whole relationship, it is an aggregation.
Aggregation is drawn like association; accept a small diamond indicates the assembly end.
The UML has two forms of part-whole relationships.
A general form called aggregation
A more restrictive form called composition.
Property of an Aggregation:-
i. Transitivity: If A is part of B and B is part of C, then A is part of C. Aggregation
ii. Anti-symmetric: If A is part of B, then B is not part of A.
Composition

Composition is a restricted form of aggregation with two additional constraints.
i. A constituent part can belong to at most one assembly.
ii. Once a constituent part has been assigned an assembly, it has a coincident lifetime with
the assembly.
Figure of Composition
Abstract Class








An abstract class is a class that has no direct instances but whose descendant classes have
direct instances.
A concrete class is a class in which it can have direct instances.
Abstraction is a process to allow focusing on most important aspects while ignoring less
important details.
In the UML notation an abstract class name is listed in an italic font. Or you may place the
keyword {abstract} below or after the name.
Use abstract class to define the signature for an operation without supplying a corresponding
method.
An abstract operation defines the signature of an operation for which each concrete subclass
must provide its own implementation.
As shown in example draw () is an abstract operation.
Within abstract class (Graphic Object), draw () is just a definition and not implementation.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
85
13 – Advanced Class Modeling



Each subclass (Circle and Rectangle) must apply method draw () in its implementation. In other
words all the super class are abstract class all the subclass are concrete class.
It is advisable to avoid concrete super class.
We can eliminate concrete super class by introducing other class. Differentiate Abstract class
and Concrete class
Multiple Inheritance


Multiple Inheritance permits the class to have more than one super class
Here subclass inherit feature form its all super class.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
86
13 – Advanced Class Modeling



In the multiple inheritance diamond problem example above Button class inherits two different
implementations of equals() while it has no own implementation of the operation.
When button.equals() is called, it is unknown which implementation from Rectangle or from
Clickable will be used.
It may arise conflicts among parallel definition creates ambiguities that implementation must
resolve.
Meta Data



Metadata is data that describes other data.
Data about data.
All the UML software models are inherently metadata, since describe the thing being modeled.
Figure: Metadata Example







Many real world applications have metadata.
Computer-language implementations also use metadata heavily.
We can consider classes as an object, but classes are meta-objects and not real-world object.
Class description objects have features, and they in turn have their own classes, which are
called Meta classes.
Treating everything as an object provides a more uniform implementation. Metadata provides
greater functionality for solving complex problem.
Accessibility of metadata varies from language to language.
Some language access metadata at compile time and some at run time.
Constraints in class modeling.



A constraint is a Boolean condition involving model elements, such as objects, classes,
attributes, links, associations and generalization sets.
A constraint restricts the values that elements can assume.
We can express constraint with
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
87
13 – Advanced Class Modeling
i. Natural Language
ii. Formal Language such as Object Constraint Language (OCL)

Constraints on object is helpful to add explicit constraint on the object of a class.
Figure: Constraint on object


As shown in above example, represents that no employee’s salary can exceed salary of
employee Boss (A constraint between two things at same time).
Another example, for maximum student in a Batch.
Figure: Constraint on object
Constraints on Generalization
 The semantics of generalization imply certain structural constraints.
 With the single inheritance the subclass is mutually exclusive.
 Furthermore, each instance of an abstract super class corresponds to exactly one subclass
instance and each instance of a concrete super class corresponds to at most one subclass
instance.
 UML defines certain keywords to demonstrate constraint.
i. Disjoint:
o The subclasses are mutually exclusive.
o Each object of subclass belongs to exactly one of the subclasses.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
88
13 – Advanced Class Modeling
ii. Overlapping:
o In an overlapping specialization, an individual of the parent class may be a member of
more than one of the specialized subclasses.
o The subclasses can share some objects.
o An object may belong to more than one subclass.
iii. Complete:
o Generalization that lists all possible subclasses.
iv. Incomplete:
o Generalization in which some of the subclasses is missing.
v. Static
o Generalization in which subclass are static in nature.
vi. Dynamic
o Generalization in which subclass are dynamic with respect to time.
Constraints on Links
 Multiplicity is constraint on cardinality of set.
 Multiplicity restricts number of object related to given object.
 Qualification also adds constraint on an association.
 An association class has a constraint that an ordinary class does not have; i.e. it derives identity
from instance of related classes.
Figure: Subset constraint between association






We favor expressing constraint in declarative manner in UML class diagram.
If we don’t use constraint in UML class modeling then we need to convert it into procedural
form before the implementation; rather this is the straight forward way.
Constraint provides criteria for measuring quality of class model.
“A good software model” captures many constraints thought its structure.
It often requires several iterations to get structure of a model right from the perspective of
constraint.
In practice we can’t enforce every constraint, but should try to enforce the important ones.
Derived Data.




A derived element is a function of one or more elements, which in turn may be derived.
A derived element is redundant, because other element completely determines it.
Classes, association and attribute may be derived.
The notation for derived elements is a slash (/) in front of element name.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
89
13 – Advanced Class Modeling
Packages.




A package is a group of elements with a common theme.
A package partitions a model, making it easier to understand and manage.
Large applications may require several tiers of packages.
The notation for a package is a box with a tab. The purpose of the tab is to suggest the enclosed
contents.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
90
14 – State Modeling
State Modeling









State Diagram explains behavior of the system.
A State Diagram is a graph whose nodes are states and arcs are transition between the states
caused by the event.
State Modeling examines changes to the object and their relationship over time.
The behavior of an entity is not only a direct consequence of its input, but it also depends on its
preceding state.
The history of an entity can best be modeled by a finite state diagram.
State diagram can show the different states of an entity also how an entity responds to various
events by changing from one state to another.
The major dynamic modeling concepts are events, which represent external stimuli, and states,
which represent values of objects.
State Diagram is a standard computer science concept/a graphical representation that relates
events and states.
State model describes:
i. Sequence of operation that occur in response of external stimuli.
ii. What the specific operation do.
iii. What they operate on.
iv. How that operation are implemented
Events and types of Events in detail.









Every event is a unique occurrence at a point in time.
It causes transitions between states.
Events might be related or unrelated. If two events are casually unrelated they are said to be
concurrent.
Event often corresponds to verb in past tense. i.e. door_opened, door_closed event.
An event happens instantaneously with regard to the time scale of an application.
It is simply an occurrence that application considers as atomic and short-lived.
Events include error conditions like motor jammed, transaction aborted, and timeout, etc.
In software modeling system we do not try to establish an ordering between concurrent events
because they can occur in any order.
The most common type of events is the signal event, the change event, and the time event.
Signal Event
 Grouping every event into event classes and gives each event class a name to indicate common
structure and behaviour is known as Signal Event.
 It is a one-way transmission of information from one object to another. It is event of sending or
receiving signal.
 The UML notation is the keyword signal in guillemets (<< >>) above the signal class name in the
top section of a box.
 The difference between signal and signal event is :
o Signal: one way transmission between object.
o Signal event: an occurrence in time.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
91
14 – State Modeling
Figure: Signal Event
Change Event
 Change event is caused by the satisfaction of Boolean expression. Whenever the expression
changes from false to true the event happens.
 The UML notation for a change event is the keyword when followed by a parenthesized Boolean
expression.
Time Events
 A time event is an event caused by the occurrence of an absolute time or the elapse of a time
interval.
 The UML notation for an absolute time is the keyword when followed by a parenthesized
expression involving time.
 This event is caused by the occurrence of an absolute time or the elapsed of a time interval.
 The notation for a time interval is the keyword after followed by a parenthesized expression
that evaluates to time duration.
Explain State






A state is an abstraction of the attribute values and links of an object.
The response of an object to an event may include an action or a change of state by the object.
A state corresponds to the interval between two events revived by an object. Events represent
points in time; states represent intervals of time.
A state has duration; it occupies an interval of time.
A state is often associated with the value of an object satisfying some condition.
In the simplest case, each enumerated value of an attribute defines a separate state.
UML notation for state:
 A rounded box containing a state name.
 In defining state we ignore attributes that do not affect the behavior of the object.
 The convention is to list the state name in Bold Face, Centered and First Letter of the State
Name should be CAPITALIZED
 The UML notation for a state – a rounded box containing a state name.
Comparing Event and State
 Though Event and States having certain symmetry between them there exists some difference.
 Event represents points in time, while states represent intervals of time.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
92
14 – State Modeling



The State having suggestive name and natural language description of its purpose.
Write the characteristics of a state Alarm Ringing.
The below figure shows for the state Alarm Ringing on a watch.
Figure: Various characterizations of a state
Transition and Condition
Transition
 A transition is a change from one state to another.
 A transition is a relationship between two states indicating that an object in the first state will
perform certain actions and enter the second state when a specified event occurs and specified
conditions are satisfied.
 On such a change of state, the transition is said to fire.
 Until the transition fires, the object is said to be in the source state; after it fires, it is said to be
in the target state.
 Transition is an instantaneous change from one state to another.
E.g. when a called phone is answered, phone line transition from ringing state to the connected
state.
Guard Condition
 Guard condition is a Boolean expression that must be true in order for a transition to occur.
E.g. Traffic light is an intersection may change if road has cars waiting.
 Guard condition is the condition fired when event occurs, but only if guard condition is true.
 Guard condition is checked only once, at a time event occurs and transition fires if condition is
true.
 If the condition is true later on, the transition does not fire then.
 UML notation for Guard condition is condition written inside square brackets [ ] on transition
and followed by an event.
 It is an optional condition.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
93
14 – State Modeling
Figure: Guarded Transitions
Comparing Guard Condition and Change Event
 Guard condition is checked only once while change event is, in effect and checked continuously.
 Guard condition is constraint, while Change event is a type of an event.
State Diagram and their types.
State Diagram
 A State Diagram is a graph whose nodes are states and arcs are transition between the states
caused by the event.
 State diagram specifies state sequence caused by an event sequence.
 State name must be unique within the scope of state diagram.
 A state diagram relates events and states. A change of state caused by an event is called
transition. All the transitions leaving a state must correspond to different events.
 The state diagram specifies the state sequence caused by an event sequence.
 If an object is in a state and an event labelling one of its transitions occurs, the object.
 Enters the state on the target end of the transition. The transition is said to fire.
 A sequence of events corresponds to a path through the graph.
 There are two types of state diagram
i. Sample State Diagrams
ii. One-Shot State Diagrams
Sample State Diagrams
 State diagram with continuous loop.
 Sample state diagram represents object with infinite life.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
94
14 – State Modeling
Figure: Sample State Diagram for Telephone Line
One-Shot State Diagrams
 One-short diagram represent object with finite lives and have initial and final states.
 Initial state is entered on creation of an object while entry of final state implies destruction of
an object. You can indicate initial and final states via entry and exit points.
 Entry points (hollow circles) and exit points (circle enclosing an “x”) appear on the state
diagram’s perimeter and may be named.
Figure: One shot State Diagram for Chess Game
State Diagram Behavior
 Application of State diagram is not just limited to the description of events.
 A full description of an object must specify what the object does in response to events.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
95
14 – State Modeling
Activity Effects
 The effect is a reference to a behavior that is executed in response to an event.
 An activity is the actual behavior that can be invoked by any number of effects.
E.g. disconnect Phone Line might be an activity that is executed in response to hang up event.
 Activities can also represent internal control operations, such as setting attributes or generating
other events.
 Such activities have no real-world counterparts but instead are mechanisms for structuring
control within an implementation.
E.g. program might increment an internal counter every time when specific event occurs.
 State diagram activity is denoted as slash (“/”) and name or description of the activity, following
the event that causes it.
 As shown in figure below, when right button is pressed, menu is displayed when it is released,
menu is erased. While menu is visible, the highlighted menu item is updated whenever cursor
moves.
Figure: Activity for pop-up menu
Do-activity
 UML notation for Do-activity is denoted as “do/” for all or part of duration that an object is in a
state.
 It can only occur within a state and can’t be attached to a transition.
 Do-activity may be interrupted by an event that is received during its execution. Such event may
or may not cause a transition out of the state containing the do-activity.
Paper Jam
Do/flash warning light
Figure: Do-activity for copy machine
Entry and Exit Activities
 We can also bind activities to entry or to exit from a state as an alternative to show the activity
on transition.
 There is no difference between binding an activity to a transition or to a state.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
96
14 – State Modeling
Figure: Entry-Exit activities






Activity which is more concise to attach the activity of a state should be specified inside the
state.
When the state is entered by an incoming transition, entry activity is performed.
An entry activity is equivalent to attaching the activity to every incoming transition.
If incoming transition already has an activity, it is performed first.
Exit activities are less common compared entry activities and occasionally useful.
Whenever state is exited, by any outgoing transition, the exit activity is performed first.
Figure: Activities on Transitions
Figure: Activities on entry to states
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
97
14 – State Modeling



This diagram shows the states of door controller. User generates depress event with a
pushbutton to open and close the door. Each event reverses the direction of the door. For
safety door must open fully before it can be closed. Motor Up and Motor Down are activities
which generates the control.
Motor generates door open and door closed events when the motion has been completed.
If a state has multiple activities, they are performed in following order:


1: Activities on incoming transition
2: Entry Activities
3: Do-Activities
4: Exit Activities
5: Activities on outgoing transition
If a Do-Activity is interrupted by transition out of the state, the exit activity is still performed.
Therefore any event can occur within a state can cause an activity to be performed.
Completion Transition
 Main purpose of state is to perform sequential activity.
 When an activity is completed, transition fires to another state.
 An arrow without an event name indicates an automatic transition that fires when activity
associated with the source state is completed.
 Such unlabeled transition is known as Completion Transition.
 Stuck Condition: Guard condition is tested only once, when event occurs. If a state has one or
more completion transition, but none of the guard condition is satisfied, then the state remains
active and may become “stuck”.
 The completion event does not occur second time, therefore no completion transition will fire
later to change the state.
 If the state has completion transition leaving it, normally the guard condition should cover
every possible outcome.
 We can use some special condition such as else to apply if all other condition is false.
 Better approach is not to use guard condition on a completion transition, instead change event
should be used.
Sending Signals
 Object can perform activity by sending signal and system of objects interacts by exchanging
signals.
 The activity “send target.S (attributes)” send signal S with given attributes to the target object
or objects.
E.g. phone line sends connect (phone number) signal to the switcher when complete number
has been dialed.
 A signal can be directed at a set of object or single object.
 If target is set of objects, each of them receives separate copy of signal and each of them
independently processes the signal.
 Race condition: If object can receive signals from more than one object, the order in which
concurrent signals are received may affect the final state. This is known as race condition.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
98
14 – State Modeling
The below diagram explain state diagram for telephone line with activities:
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
99
15 – Interaction Modeling
Interaction Modeling











Interaction model is the third leg of the tripod and describes interaction with the system.
Class model describes object in the system and relationship among them.
State model describes life history of an object.
Interaction model describes how the object interacts to produce useful results.
Interaction model and state software model describes whole behavior of the system.
Interaction can be modeled at different level of abstraction. At higher level, use case describes
how a system interacts with outside actors.
Each use case represents piece of functionality that a system provides to its user.Use cases are
helpful for capturing informal requirements.
Sequence diagram provides more detail and show the messages exchanged among a set of
objects over the time.
Sequence diagrams are good for showing the behavior sequence seen by users of a system.
Activity diagrams provide further detail and show the flow of control among the steps of
computation.
Activity diagram documents the steps necessary to implement an operation or a business
process in a sequence diagram.
Use case Models


Use Cases identifies the functionality of a system and organize it according to the perspective of
users.
Use Cases describe complete transactions and are therefore less likely to omit necessary steps.
i. First determine the system
ii. Ensure that actors are focused
iii. Each use case must provide value to users.
iv. For example, dial a telephone number is not a good use case for a telephone system
v. Relate use cases and actors
vi. Remember that use cases are informal
vii. Use cases can be structured
Use Case Diagram
Introduction:
 A use case diagram describes how a system interacts with outside actors.
 It is a graphical representation of the interaction among the elements and system.
 Each use case representation a piece of functionality that a system provides to its user.
 Use case identifies the functionality of a system.
 Use case diagram allows for the specification of higher level user goals that the system must
carry out.
 These goals are not necessarily to tasks or actions, but can be more general required
functionality of the system.
 You can apply use case to capture the intended behavior of the system you are developing,
without having to specify how that behavior is implemented.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
100
15 – Interaction Modeling


A use case diagram at its simplest is a representation of a user's interaction with the system and
depicting the specifications of a use case.
A use case diagram contains four components.
i. The boundary, which defines the system of interest in relation to the world around it.
ii. The actors, usually individuals involved with the system defined according to their
roles.
iii. The use cases, which the specific roles are played by the actors within and around the
system.
iv. The relationships between and among the actors and the use cases.
Purpose:
 The main purpose of the use case diagram is to capture the dynamic aspect of a system.
 Use case diagram shows, what software is suppose to do from user point of view.
 It describes the behavior of system from user’s point.
 It provides functional description of system and its major processes.
 Use case diagram defines the scope of the system you are building.
When to Use: Use Cases Diagrams
 Use cases are used in almost every project.
 They are helpful in exposing requirements and planning the project.
 During the initial stage of a project most use cases should be defined.
Use Case Notations
No.
1
Name
System boundary
2
Use case
Notation
Use Case
3
Actor
Description
The scope of a system can be represented by a
system boundary. The use cases of the system
are placed inside the system boundary, while the
actors who interact with the system are put
outside the system.
The use cases in the system make up the total
requirements of the system.
A use case represents a user goal that can be
achieved by accessing the system or software
application.
Actors are the entities that interact with a
system. Although in most cases, actors are used
to represent the users of system, actors can
actually be anything that needs to exchange
information with the system.
So an actor may be people, computer hardware,
other systems, etc. Note that actor represent a
role that a user can play, but not a specific user.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
101
15 – Interaction Modeling
4
Association
Actor and use case can be associated to indicate
that the actor participates in that use case.
Therefore, an association corresponds to a
sequence of actions between the actor and use
case in achieving the use case.
A generalization relationship is used to represent
inheritance relationship between model
elements of same type.
5
Generalization
6
Include
An include relationship specifies how the
behavior for the inclusion use case is inserted
into the behavior defined for the base use case.
7
Extends
8
Constraint
An extend relationship specifies how the
behavior of the extension use case can be
inserted into the behavior defined for the base
use case.
Show condition exists between actors an
activity.
9
Package
Package is defined as collection of classes.
Classes are unified together using a package.
10
Interface
11
Note
Interface is used to connect package and usecase. Head is linked with package and tail linked
with usecase.
Note is generally used to write comment in usecase diagram.
12
Anchor
Anchor is used to connect a note the use case in
use case diagram.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
102
15 – Interaction Modeling
Draw Use case diagram for Library management System
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
103
15 – Interaction Modeling
Draw Use-case Diagram For ATM System
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
104
15 – Interaction Modeling
Draw Use-case diagram for online restaurant system
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
105
15 – Interaction Modeling
Draw Use-case for Online Reservation System
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
106
15 – Interaction Modeling
Draw Use-case diagram for online shopping system
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
107
15 – Interaction Modeling
Sequance models
Introduction
 Sequence diagrams model the dynamic aspects of a software system.
 The emphasis is on the “sequence” of messages rather than relationship between objects.
 A sequence diagram maps the flow of logic or flow of control within a usage scenario into a
visual diagram enabling the software architect to both document and validate the logic during
the analysis and design stages.
 Sequence diagrams provide more detail and show the message exchanged among a set of
objects over time.
 Sequence diagrams are good for showing the behavior sequences seen by users of a diagram
shows only the sequence of messages not their exact timing.
 Sequence diagrams can show concurrent signals.
Purpose
 The main purpose of this diagram is to represent how different business objects interact.
 A sequence diagram shows object interactions arranged in time sequence.
 It depicts the objects and classes involved in the scenario and the sequence of messages
exchanged between the objects needed to carry out the functionality of the scenario.
When to use : Sequence Diagram
 Sequence diagram can be a helpful modeling tool when the dynamic behavior of objects needs
to be observed in a particular use case or when there is a need for visualizing the “big picture of
message flow”. A company’s technical staff could utilize sequence diagrams in order to
document the behavior of a future system.
 It is during the design period that developers and architects utilize the diagram to showcase the
system’s object interactions, thereby putting out a more fleshed out overall system design.
Sequence Diagram Notations
Sr. No. Name
Notation
Desription
1
Object
It represents the existence of an
object of a particular time.
2
Life line
Lifeline represents the duration
during which an object is alive and
interacting with other objects in the
system. It is represented by dashed
lines.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
108
15 – Interaction Modeling
3
Scope
It shows the time period during
which an object or actor is
performing an action.
4
Message
transition
To send message from one object to
another.
5
Message
attribute
with
To send message
particular Attribute
6
Message
constraint
with
To send message from one object to
other vy some constraint.
7
Acknowledgement
It
represent
communication
between
objects
conveys
acknowledgement.
8
Self message
Self message occurs when an object
sends a message to itself.
9
Recursive
message
Self message occurs when an object
sends a message to itself within
recursive scope.
with
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
some
109
15 – Interaction Modeling
Sequence Diagram for library management system
Issue book
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
110
15 – Interaction Modeling
Return book
Book not available
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
111
15 – Interaction Modeling
Sequence Diagram For ATM Management System:-
Create account
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
112
15 – Interaction Modeling
Transaction
Exceptional case
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
113
15 – Interaction Modeling
Sequence diagram for Online shopping system to place order
Supply order
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
114
15 – Interaction Modeling
Product not available
Product Exchange
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
115
15 – Interaction Modeling
Sequence diagram for Bus reservation system:Reservation
Ticket Not available
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
116
15 – Interaction Modeling
Activity Diagram
Introduction
 An activity diagram is a type of flow chart with additional support for parallel behavior.
 This diagram explains overall flow of control.
 Activity diagram is another important diagram in UML to describe dynamic aspects of the
system.
 Activity diagram is basically a flow chart to represent the flow from one activity to another
activity
 The activity can be described as an operation of the system.
 The control flow is drawn from one operation to another. This flow can be sequential, branched
or concurrent. This distinction is important for a distributed system.
 Activity diagrams deals with all type of flow control by using different elements like fork, join
etc.
Purpose
 Contrary to use case diagrams, in activity diagrams it is obvious whether actors can perform
business usecases together or independently from one another.
 Activity diagrams allow you to think functionally.
When to use : Activity Diagrams
 Activity diagrams are most useful when modeling the parallel behavior of a multithreaded
system or when documenting the logic of a business process.
 Because it is possible to explicitly describe parallel events, the activity diagram is well suited for
the illustration of business processes, since business processes rarely occur in a linear manner
and often exhibit parallelisms.
 This diagram is useful to investigate business requirements at a later stage.
 An activity diagram is drawn from a very high level. So it gives high level view of a system. This
high level view is mainly for business users or any other person who is not a technical person.
 This diagram is used to model the activities which are nothing but business requirements.
 So the diagram has more impact on business understanding rather implementation details.
Activity Diagram Notations
No.
1
Name
Activity
Symbol
Description
Represent individual activity of system.
Activity
2
Transition
Represents flow of data from one activity to another.
3
Decision
Decision node is a control node that accepts tokens
on one or more incoming edges and selects outgoing
edge from two or more outgoing flows. The notation
for a decision node is a diamond-shaped symbol.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
117
15 – Interaction Modeling
4
Initial activity
5
Final activity
6
Fork
7
Join
Initial node is a control node at which flow starts
when the activity is invoked. Activity may have more
than one initial node. Initial nodes are shown as a
small solid circle.
Final node is a control final node that stops all flows in
an activity. Activity final nodes are shown as a solid
circle with a hollow circle inside. It can be thought of
as a goal notated as "bull’s eye," or target.
A fork in the activity diagram has a single incoming
transition and multiple outgoing transitions exhibiting
parallel behavior.The incoming transition triggers the
parallel outgoing transitions.
A join in the activity diagram synchronizes the parallel
behavior started at a fork. Join ascertains that all the
parallel sets of activities (irrespective of the order) are
completed before the next activity starts. It is a
synchronization point in the diagram. Each fork in an
activity diagram has a corresponding join where the
parallel behavior terminates.
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
118
15 – Interaction Modeling
Activity Diagram for Library Management System
Issue and return book
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
119
15 – Interaction Modeling
Diagram for ordering new book
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
120
15 – Interaction Modeling
Activity diagram for ATM
Verify PIN number
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
121
15 – Interaction Modeling
Transaction
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
122
15 – Interaction Modeling
Activity Diagram for Online Restaurant Management System
Place order
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
123
15 – Interaction Modeling
Payment
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
124
15 – Interaction Modeling
Activity Diagram for Online Reservation System
Booking Process
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
125
15 – Interaction Modeling
Server Operation
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
126
15 – Interaction Modeling
Activity diagram for Online Shopping
Purchase Product
Prof. Arjun Bala, Prof. Chirag Patel, CE Department | 2150704 – Object Oriented Programming with Java
127
Download PDF
Similar pages