Java Concurrency Specs: Write a program that bounces a blue ball inside a JPanel

Question

Java Concurrency

Specs: Write a program that bounces a blue ball inside a JPanel. The ball should begin moving with a mousePressed event. When the ball hits the edge of the JPanel, it should bounce off the edge and continue in the opposite direction. The ball should be updated using a Runnable. A new ball should be added each time the user clicks the mouse. The program should support creation up to 20 balls. Randomly choose the color for each new ball yet make the initial ball a blue one. Pressing space should pause the movement. To continue moving the balls you should press space again.

Explanation / Answer

import javax.swing.JFrame;
import java.util.Random;
public class Ball implements Runnable
{
private boolean xUp; // controls whether ball is moving up or down
private boolean yUp; // controls whether ball is moving left or right
private int x; // horizontal position of ball
private int y; // vertical position of ball
private int xDx; // change in horizontal position of ball
private int yDy; // change in vertical position of ball
private final int MAX_X = 200; // horizontal edge of JPanel
private final int MAX_Y = 200; // vertical edge of JPanel
private JFrame parent; // parent window of ball
private Random generator = new Random();

public Ball( JFrame window, int xPos, int yPos )
{
xUp = false; // set ball to moving to left
yUp = false; // set ball to moving up
xDx = 1; // set ball to move one pixel horizontally at a time
yDy = 1; // set ball to move one pixel vertically at a time
x = xPos; // set ball to horizontal position of mouse press   
y = yPos; // set ball to vertical position of mouse press
parent = window; // set parent window of ball
} // end Ball constructor
// bounces ball perpetually until window is closed
public void run()
{
while ( true ) // infinite loop
{
try
{
Thread.sleep( 20 ); // sleep for 20 milliseconds
} // end try
// process InterruptedException during sleep
catch ( InterruptedException exception )
{
exception.printStackTrace();
  
} // end catch

// determine new x position
if ( xUp == true )
x += xDx; // move ball right
else x -= xDx; // move ball left
// determine new y position
if ( yUp == true )
y += yDy; // move ball down
else y -= yDy; // move ball up
if ( y <= 0 ) // if bounce off top of JPanel
{
yUp = true; // ball is moving down
yDy = generator.nextInt( 5 ) + 2; // change vertical move
} // end if else
if ( y >= MAX_Y - 10 ) // if bounce off bottom of JPanel
{
yUp = false; // ball is moving up
yDy = generator.nextInt( 5 ) + 2; // change vertical move
} // end else if
if ( x <= 0 ) // if bounce off right of JPanel
{
xUp = true; // ball is moving right
xDx = generator.nextInt( 5 ) + 2; // change horizontal move
} // end if else
if ( x >= MAX_X - 10 ) // if bounce off left of JPanel
{
xUp = false; // ball is moving left
xDx = generator.nextInt( 5 ) + 2; // change horizontal move
} // end else if parent.repaint(); // repaint window
} // end while
} // end method run
// get horizontal position of ball
public int getX()
{
return x; // return x value
} // end method getX
// get vertical position of ball
public int getY()
{ return y; // return y value
} // end method getY
} // end class Ball

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