import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.*;
import javax.swing.*;
/**
Shows an animated bouncing ball.
*/
public class Bounce
{
public static void main (String [] args)
{
JFrame frame = new BounceFrame ();
frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
frame.show ();
}
}
/**
The frame with canvas and buttons.
*/
class BounceFrame extends JFrame implements MouseMotionListener
{
/**
Constructs the frame with the canvas for showing the
bouncing ball and Start and Close buttons
*/
public BounceFrame ()
{
setSize (WIDTH, HEIGHT);
setTitle ("Bounce");
Container contentPane = getContentPane ();
canvas = new BallCanvas ();
contentPane.add (canvas, BorderLayout.CENTER);
JPanel buttonPanel = new JPanel ();
addButton (buttonPanel, "Start",
new ActionListener ()
{
public void actionPerformed (ActionEvent evt)
{
addBall ();
}
});
addButton (buttonPanel, "Close",
new ActionListener ()
{
public void actionPerformed (ActionEvent evt)
{
System.exit (0);
}
});
contentPane.add (buttonPanel, BorderLayout.SOUTH);
}
/**
Adds a button to a container.
@param c the container
@param title the button title
@param listener the action listener for the button
*/
public void addButton (Container c, String title,
ActionListener listener)
{
JButton button = new JButton (title);
c.add (button);
button.addActionListener (listener);
}
/**
Adds a bouncing ball to the canvas and makes
it bounce 1,000 times.
*/
public void addBall ()
{
try
{
Ball b = new Ball (canvas);
canvas.add (b);
for (int i = 1; i <= 1000; i++)
{
b.move ();
Thread.sleep (5);
}
}
catch (InterruptedException exception)
{
}
}
private BallCanvas canvas;
public static final int WIDTH = 450;
public static final int HEIGHT = 350;
}
/**
The canvas that draws the balls.
*/
class BallCanvas extends JPanel
{
/**
Add a ball to the canvas.
@param b the ball to add
*/
public void add (Ball b)
{
balls.add (b);
}
public void paintComponent (Graphics g)
{
super.paintComponent (g);
Graphics2D g2 = (Graphics2D)g;
for (int i = 0; i < balls.size (); i++)
{
Ball b = (Ball)balls.get (i);
b.draw (g2);
}
}
private ArrayList balls = new ArrayList ();
}
/**
A ball that moves and bounces off the edges of a
component
*/
class Ball
{
/**
Constructs a ball in the upper left corner
@c the component in which the ball bounces
*/
public Ball (Component c) { canvas = c; }
/**
Draws the ball at its current position
@param g2 the graphics context
*/
public void draw (Graphics2D g2)
{
g2.fill (new Ellipse2D.Double (x, y, XSIZE, YSIZE));
}
/**
Moves the ball to the next position, reversing direction
if it hits one of the edges
*/
public void move ()
{
x += dx;
y += dy;
if (x < 0)
{
x = 0;
dx = -dx;
}
if (x + XSIZE >= canvas.getWidth ())
{
x = canvas.getWidth () - XSIZE;
dx = -dx;
}
if (y < 0)
{
y = 0;
dy = -dy;
}
if (y + YSIZE >= canvas.getHeight ())
{
y = canvas.getHeight () - YSIZE;
dy = -dy;
}
canvas.paint (canvas.getGraphics ());
}
private Component canvas;
private static final int XSIZE = 15;
private static final int YSIZE = 15;
private int x = 0;
private int y = 0;
private int dx = 2;
private int dy = 2;
}
