Source of PlayBalloon.java

Structures and functions

public class PlayBalloon extends Applet 
class Balloon

  1: import java.applet.Applet;
  2: import java.awt.*;
  3: import java.awt.event.*;
  4: public class PlayBalloon extends Applet 
  5:     implements ActionListener {
  6:     private Button grow, shrink;
  7:     private Balloon myBalloon;

  9:     public void init() {
 10:         grow = new Button ("Grow");
 11:         add (grow);
 12:         grow.addActionListener(this);
 13:     
 14:         shrink = new Button ("Shrink");
 15:         add (shrink);
 16:         shrink.addActionListener(this);
 17:     
 18:         myBalloon = new Balloon (20, 50, 50);
 19:     }

 21:     public void actionPerformed(ActionEvent event) {
 22:         if (event.getSource() == grow)
 23:             myBalloon.changeSize(10);
 24:         if (event.getSource() == shrink)
 25:             myBalloon.changeSize(-10);
 26:         repaint();
 27:     }

 29:     public void paint (Graphics g) {
 30:         myBalloon.display(g);
 31:     }
 32: }

 34: class Balloon{
 35:     private int diameter;
 36:     private int xCoord, yCoord;

 38:     public Balloon (int initialDiameter, int initialX, int initialY) {
 39:         diameter = initialDiameter;
 40:         xCoord = initialX;
 41:         yCoord = initialY;
 42:     }

 44:     public void changeSize (int change) {
 45:         diameter = diameter + change;
 46:     }

 48:     public void display (Graphics g) {
 49:         g.drawOval (xCoord, yCoord, diameter, diameter);
 50:     }
 51: }