Hello,
I am relatively new to Java. I would like to know how to add additional threads to this applet. Particularly adding additional balls that bounce at the same time. I think the problem lies in my mousePressed event. The program will start a new ball, but make the existing ball disappear. Any help would be greatly appreciated.

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class Ball extends JApplet implements Runnable, MouseListener {
   private Thread[] blueBall = new Thread[MAX_BALL_COUNT];
   private boolean xUp, yUp, bouncing;
   private int x, y, xDx, yDy;
   int ballcount = 0;
   final private static int MAX_BALL_COUNT = 20;

   
   //init is called by the browser to inform the applet that Ball has been loaded
   public void init()
   {
      xUp = false; 
      yUp = false; 
      xDx = 1; 
      yDy = 1; 
      addMouseListener( this ); 
      bouncing = false;
   }
   
   
   public void mousePressed( MouseEvent e ) 
   {
      if ( ballcount < MAX_BALL_COUNT ) { 
         x = e.getX(); //PB: get the X position
         y = e.getY(); //PB: get the Y position
         blueBall[ballcount] = new Thread( this ); 
         bouncing = true; 
         
         blueBall[ballcount].start();
         ballcount++;
      }
   }

   public void stop()
   {
      if ( blueBall != null ) 
         blueBall = null;      
   }

    public void start ()
    {
        for(int i = 0; i < blueBall.length; i++)
            if(blueBall[i] != null)
                blueBall[i].start();
    }



   
   public void paint( Graphics g )
   {
      super.paint( g );

      if ( bouncing ) {
         g.setColor( Color.blue );
         g.fillOval( x, y, 10, 10 );
      }
   }
   
   public void run()
   {
      while ( true ) { 

         try {
            Thread.sleep( 100 ); 
         }
         // PB: process exception during sleep
         catch ( Exception e ) { 
            System.err.println( "Exception: " + e.toString() );
         }
         
        
         if ( xUp == true )
            x += xDx;
         else
            x -= xDx;
          
         if ( yUp == true )
            y += yDy;
         else
            y -= yDy;

         if ( y <= 0 ) { 
            yUp = true;            
            yDy = ( int ) ( Math.random() * 5 + 2 );   
        }
         else if ( y >= 190 ) { 
            yDy = ( int ) ( Math.random() * 5 + 2 ); 
            yUp = false;
         }

         if ( x <= 0 ) { 
            xUp = true;
            xDx = ( int ) ( Math.random() * 5 + 2 ); 
         }
         else if ( x >= 190 ) { 
            xUp = false;
            xDx = ( int ) ( Math.random() * 5 + 2 ); 
         }

        repaint(); 
      }
   }

   public void mouseExited( MouseEvent e ) {}
   public void mouseClicked( MouseEvent e ) {}
   public void mouseReleased( MouseEvent e ) {}
   public void mouseEntered( MouseEvent e ) {}     
}

Maybe this will do the trick?

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class Ball extends JApplet implements MouseListener {
   private MyThread blueBall[] = new MyThread[MAX_BALL_COUNT];
   private boolean bouncing; // xUp, yUp
   //private int x, y, xDx, yDy;
   int ballcount = 0;
   final private static int MAX_BALL_COUNT = 20;


   //init is called by the browser to inform the applet that Ball has been loaded
   public void init()
   {
      //xUp = false;
      //yUp = false;
      //xDx = 1;
      //yDy = 1;
      bouncing = true;
      addMouseListener( this );
      Thread repaintThread = new Thread(rt);
      repaintThread.setPriority(1);
      repaintThread.setDaemon(true);
      repaintThread.start();
   }


   public void mousePressed( MouseEvent e )
   {
      if ( ballcount < MAX_BALL_COUNT ) {

         blueBall[ballcount] = new MyThread();
         blueBall[ballcount].x = e.getX(); //PB: get the X position
         blueBall[ballcount].y = e.getY(); //PB: get the Y position
         Thread temp = new Thread(blueBall[ballcount]);
         temp.setPriority(2);
         temp.setDaemon(true);
         temp.start();
         ballcount++;
      }
   }

   public void stop()
   {
      //if ( blueBall != null )
      //   blueBall = null;
      for(MyThread element : blueBall){
		  if(element != null)
		  	element.running = false;
	  }
	  bouncing = false;

   }

    public void start ()
    {
    //    for(int i = 0; i < blueBall.length; i++)
    //        if(blueBall[i] != null)
    //            blueBall[i].start();
    }

	Runnable rt = new Runnable(){
		@Override public void run(){
			while(bouncing){
				try{
					Thread.sleep(25);
				}catch(Exception e){}
				repaint();
			}
		}
	};


   public void paint( Graphics g )
   {
      super.paint( g );

      if ( bouncing ) {
         g.setColor( Color.blue );

         for(MyThread element : blueBall){
			if(element != null)
         	   g.fillOval( element.x, element.y, 10, 10 );
		 }
      }
   }

   public class MyThread implements Runnable{
	   public int x = 0, y = 0;
	   private int xDx = 1, yDy = 1;
	   private boolean xUp =false, yUp = false;
	   public boolean running = true;

	   public void run()
	   {
		  while ( running ) {

			 try {
				Thread.sleep( 100 );
			 }
			 // PB: process exception during sleep
			 catch ( Exception e ) {
				System.err.println( "Exception: " + e.toString() );
			 }


			 if ( xUp == true )
				x += xDx;
			 else
				x -= xDx;

			 if ( yUp == true )
				y += yDy;
			 else
				y -= yDy;

			 if ( y <= 0 ) {
				yUp = true;
				yDy = ( int ) ( Math.random() * 5 + 2 );
			}
			 else if ( y >= 190 ) {
				yDy = ( int ) ( Math.random() * 5 + 2 );
				yUp = false;
			 }

			 if ( x <= 0 ) {
				xUp = true;
				xDx = ( int ) ( Math.random() * 5 + 2 );
			 }
			 else if ( x >= 190 ) {
				xUp = false;
				xDx = ( int ) ( Math.random() * 5 + 2 );
			 }

			//repaint();
		  }
	   }
	}

   public void mouseExited( MouseEvent e ) {}
   public void mouseClicked( MouseEvent e ) {}
   public void mouseReleased( MouseEvent e ) {}
   public void mouseEntered( MouseEvent e ) {}
}

--though, I strongly discourage using raw Threads. Use threads from java.util.concurrent.*

Alex,
Thank you very much! That was awesome. It is greatly appreciated.

AllenB

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