// BallWorld - version 7

          import java.awt.*;

          public class BallWorld extends Frame

          {

          ////////////////////////////////

          ////////// variables ///////////

          ////////////////////////////////

          // application variables

          // variables for width and height of frame

          public static final int frameWidth = 600;

          public static final int frameHeight = 400;

          /// NEW NEW NEW - array of refernces to Ball objects

          private Ball balls[];

          // a counter - so we can paint the ball more than once

          private int counter;

          ////////////////////////////////

          ///////////// methods //////////

          ////////////////////////////////

          ////////// method main ///////////

          // sequence of instrucions for main program

          static public void main (String [] args)

          {

          BallWorld world = new BallWorld ();

          world.show ();

          }

          ////////// method BallWorld ///////////

          private BallWorld ()

          {

          // set size and title of our application window

          setSize(frameWidth, frameHeight);

          setTitle("Ball World");

          // NEW NEW NEW - set up "balls" to hold 5 balls

          balls = new Ball[5];

          // NEW NEW NEW - set up each of the 5 balls

          balls[0] = new Ball(100, 100, 50, 4, 5);

          balls[1] = new Ball(200, 200, 25, -3, -2);

          balls[2] = new Ball(50, 50, 5, 1, -1);

          balls[3] = new Ball(200, 50, 10, -10, -15);

          balls[4] = new Ball(75, 200, 75, -1, 1);

          // NEW NEW NEW - make the balls different colours

          balls[1].setColor( Color.green );

          balls[2].setColor( Color.red );

          balls[3].setColor( Color.yellow );

          balls[4].setColor( Color.green );

          // set out counter to zero

          counter = 0;

          }

          private void bounce(Ball ball)

          {

          // check for left of frame collision (X value too small)

          if ( ball.getX() < 0 )

          ball.setMotion( -ball.getXMotion(), ball.getYMotion() );

          // check for right of frame collision (X value too large)

          if ( ball.getX() > frameWidth )

          ball.setMotion(-ball.getXMotion(), ball.getYMotion());

          // check for top of frame collision (Y value too small)

          if ( ball.getY() < 0 )

          ball.setMotion(ball.getXMotion(), -ball.getYMotion());

          // check for bottom of frame collision (Y value too large)

          if ( ball.getY() > frameHeight )

          ball.setMotion(ball.getXMotion(), -ball.getYMotion());

          }

          ////////// method paint ///////////

          public void paint(Graphics g)

          {

          // NEW NEW NEW - display and move all 5 balls

          for( int i = 0; i < balls.length; i++)

          {

          balls[i].paint( g );

          balls[i].move();

          }

          pause( 20 );

          // NEW NEW NEW - call method "bounce" for all 5 balls

          for( int i = 0; i < balls.length; i++)

          bounce( balls[i] );

          counter = counter + 1;

          if (counter < 500)

          repaint();

          else

          System.exit(0);

          }

          ////////// method pause ///////////

          private void pause(int numMilliseconds)

          {

          // use a Java libary routine to pause a little

          try{ Thread.sleep( numMilliseconds ); } catch (InterruptedException e){}

          }

          } // class BallWorld