Lab text as pdf

Lab text as pdf
Lab 10: User Interactions
In this lab you will learn a little about programming user interactions using
the Model-View-Control pattern for organizing the responsibilities.
The JPT library allows you to concentrate on the key concepts and avoid
the pitfalls of multitude of details, typically associated with GUI programming.
The Existing Balloon Controls
Examine briefly the code already supplied with the lab. The code consists
of the following classes:
• class Balloon represents one balloon object, allows the user to move
it, paint it, and to compare two balloons for closeness to the top of
the graphics window.
• interface BalloonInput contains two methods: demandBalloon()
and requestBalloon().
• class ConsoleBalloonInput implements the BalloonInput interface
for the input from the console.
• class BalloonInputView defines a GUI to request the user input for
the data needed to initialize one Balloon instance. It contains two
TextFieldViews, one SliderView, and one ColorView.
• class GUIBalloonInput implements the BalloonInput interface for
extracting the user input from the BalloonInputView GUI.
Run the code, and note the behavior in response to the various buttons.
Answer the following questions:
1. Read the code for the class Balloon. Add the method eraseBalloon
which will paint the balloon in a white color (Color.white. Make sure
you have the examples and tests for this method.
2. Read the code for the method testConsoleInput in the class SimpleTests.
Describe to your partner (find one, just for this exercise) what the
method does. Look at the ConsoleBalloonInput class to make sure
you understand how the input is being read in.
3. Print the code for the class BalloonInputView. Find the code for
the action for the new button. Currently, it only sets the value of the
Balloon instance variables. Add to this action a call to the method
which paints the balloon, from the class Balloon. Make sure it
4. Find all places where the xTVF is defined or used. Talk with your
partner and make sure you understand what is the purpose of each of
these code segments.
Using a similar technique, define a new TextFieldView named rTFV,
to represent the numerical value of the Balloon radius.
Test the behavior of the slider. Does it have any effect on the balloon?
Does it have any effect on the value displayed in the rTFV field?
Change the value of the rTFV field. Does it affect the slider? Does it
affect the balloon?
5. Define two new SimpleActions and the corresponding methods — an
rTFVaction and a SliderAction. It does not matter what you choose
for the label, because we are not going to use the actions with a button.
The first one void rTFVaction will be invoked when the value in the
field rTFV changes. It should then set the value of the balloon radius
and the value of the rSlider to the value displayed in the rTFV. To
set the state of the rSlider use the method
rSlider.setViewState("" + b.radius);
The second method void rSliderAction() will be invoked every time
the location of the slider (and the value it represents) changes. It must
then change the radius of the balloon and set the view state of the
rTFV calling the method setViewState in a manner similar to the
above. If you run the program now, you may be surprised to see that
these changes have no effect. Can you think of the way to test that
the methods work correctly?
6. Now you have to tell the rSlider and the rTFV to perform this action
when their values change. The following two statements have to be
added at the end of the method void createViews():
rTFV.addActionListener(rTFVaction); and
Test that this works.
7. Now that you have seen the method setViewState, add such method
to the class BalloonInputView. To see that is works, we need to
modify some of the fields of a Balloon instance and invoke the method.
Try it.
8. In the last part you will control the balloon with the mouse. The
first thing you need to do is to change the manner in which the
GUI is displayed. Look at the code in the class SimpleTests for
the method testBalloonControl(). Replace the line which calls the
method showOKDialog with the following:
JPTFrame.createQuickJPTFrame("Balloon Control", bc);
This places the BalloonControl into a window that runs i n its own
thread, i.e. independently of the rest of the application. That allows
the rest of the appplication to watch out for the mouse movement and
clicks inside of the graphics window.
9. The first mouse action you will build will increase the radius of the
balloon by ten, every time you click the mouse. All of this is in the
class BalloonControl. Start by defining the method protected
click(MouseEvent mevt) which does the following:
• Print into the console a message that the mouse was clicked.
• Erase the balloon
• Increase the balloon radius by 10
• Set the view state of the BalloonInputView bView to the current
values of the balloon. (Only the radius has changed, but it is
easier to let the BalloonView do the whole job by invoking the
method setViewState.
• Finally, paint the changed balloon.
10. We need to ask the window to provide us with its MouseActionAdapter
as follows:
• After the definition of the BufferedPanel, add the definition:
public MouseActionAdapter mouseAdapter;
• Inside of the constructor for the class BalloonControl first initialize the mouseAdapter as follows:
mouseAdapter = window.getMouseActionAdapter();
• Add the action to perform when the mouse is clicked as follows:
// respond to mouse clicks
new MouseAction() {
public void mouseActionPerformed(MouseEvent mevt){
At this point you should test that your program runs as you
• Finally, you will make the balloon move when the mouse moves.
Do all the steps you have done for the clicked action, but do not
get a new mouseAdapter. The following code will add the action:
// track mouse motions
new MouseAction() {
public void mouseActionPerformed(MouseEvent mevt){
Inside of the track method get the coordinates of the mouse as
b.x = mevt.getX(); and
b.y = mevt.getY();
and see what your program does. (Probably nothing - you still
have to erase the old balloon, before you make the changes, paint
the new balloon, and as a courtesy, set the view state for the
view.) Now you should have fun.
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