Double Buffering Problem

I decided to use double buffering to eliminate the flashing in my applet. But there is a problem. Instead of things moving slowly... everything is saved on to the screen and stays there. For example... the ball is suppose to move like any ball would... but instead it creates a line of balls that don't disappear. How can I fix this?

import java.applet.Applet; 
import java.awt.*; 
import java.awt.event.*; 
import javax.swing.*;   
 
/*//////////////////// 
Pong////////////////// 
Martin vanPutten////// 
Woodstock High School/ 
*/////////////////////  
 
public class Pong extends Applet implements Runnable   
 
{ // Pong Applet.   
 
int x = 1; // Controller Pad Width.
int y = 215; // Controller Pad Length.
int xx = 789; //Computer Pad Width.
int yy = 210; // Computer Pad Length.
int X = 10; // Ball Width.
int Y = 235; // Ball Length.
int pTop; // Center Point Of Ball Hitting Top Of Paddle.
int pBottom; // Center Point Of Ball Hitting Bottom Of Paddle.
int Speed = -200;
int t = 0; // Top Border.
int b = 420; // Bottom Border. 
int yIncrement; // Balls Y-Axis Incrementing. 
int xIncrement; // Balls X-Axis Incrementing. 
 int frame; // Frames.
    int delay; // Delay Time.
    
    Thread animator; // Animator Thread.
    
Timer timerUp; // Timer Up Pad. 
Timer timerDown; // Timer Down Pad. 
Timer timerBall; // Timer Ball. 
Timer timerAI; // Timer AI.

Tester Test1 = new Tester (); // Performs Test Class. 
Exam Test2 = new Exam (); // Performs Exam Class.

public void init ()  
 
{ // Initialize.  
 
 String str = getParameter ("fps"); // Gets Parameters For Double Buffering.
int fps = (str != null) ? Integer.parseInt (str) : 10; // Initializes Integer fps.
delay = (fps > 0) ? (1000 / fps) : 100; // Delay Time.
 
setBackground (Color.black); // Background Color.

timerUp = new Timer (-200, new TimeListenerUp ()); // Pulls TimeListenerUp Class. 
timerDown = new Timer (-200, new TimeListenerDown ()); // Pulls TimeListenerDown Class. 
timerBall = new Timer (Speed, new TimeListenerBall ()); // Pulls TimeListenerBall Class. 
timerAI = new Timer (-200, new TimeListenerAI ()); // Pulls TimeListenerAI Class.

Test1.trial (1, 0); // Test.
Test2.trials (1, 0); // Second Test.

addKeyListener (new KeyAdapter () // Key Listener.  
 
{ // Keys.              
 
public void keyPressed (KeyEvent keP)              
 
{ // Keys Pressed.                  
 
if (keP.getKeyCode () == KeyEvent.VK_ENTER) // Starts Pong.  
 
{ // Starts Components.  
 
timerBall.start (); // Start Ball Component. 
timerAI.start (); // Start AI Component.

Test1.trial (0, 1); // Test.
    repaint ();
       
} //End Starts Components.  
 
if (keP.getKeyCode () == KeyEvent.VK_UP) // Start Up.         
timerUp.start ();          
 
if (keP.getKeyCode () == KeyEvent.VK_DOWN) // Start Down.         
timerDown.start ();

if (y <= t)  
 
{ // Up Restriction.  
 
timerUp.stop (); 
y = 0;  
 
} // End Up Restriction. 
 
if (y >= b)

{ // Down Restriction.

timerDown.stop (); 
y = 420;

} // End Down Restriction.

} // End Keys Pressed.

public void keyReleased (KeyEvent keR)

{ // Keys Released.

if (keR.getKeyCode () == KeyEvent.VK_UP) // Stop Up.         
timerUp.stop ();

if (keR.getKeyCode () == KeyEvent.VK_DOWN) // Stop Down.         
timerDown.stop ();

} // Keys Released.

} // End Keys.

); // End Key Listener.

} // End Initialize.

public void start ()

{ // Starts Animator.

animator = new Thread (this);
animator.start ();
    
    } // End Starts Animator.

public void run ()

{ // Runs Animation.

long tm = System.currentTimeMillis (); // Remembers The Starting Time.
while (Thread.currentThread () == animator)

{ // Creates Animation.
    
    repaint (); // Display The Next Frame Of Animation.
    
    try 
    
    { // Delay Depending On How Far We Are Behind.

tm += delay;

Thread.sleep (Math.max (0, tm - System.currentTimeMillis ()));
    
    } // End Delay Depending On How Far We Are Behind.
    
    catch (InterruptedException e) 
    
    { // Break.

break;
    
    } // End Break.
    
    frame++; // Advance The Frame.

} // End Creates Animation.
    
    } // End Runs Animation.

public void stop ()

{ // Stops Animation.

animator = null;
    
    } // End Stops Animation.
    
public void paint (Graphics g)

{ // Updates Existing Graphics.

update (g);

} // End Updates Existing Graphics.

public void update (Graphics g)

{ // Graphics.

Graphics2D g2d = (Graphics2D) g; // 2D Graphics.
    
    int screenRes = Toolkit.getDefaultToolkit ().getScreenResolution (); // Screen Resolution.
    int fontSize = (int) Math.round (40.0 * screenRes / 72.0); // Font Size.
 
    Font font = new Font("Arial", Font.PLAIN, fontSize); // Font Style.

if (Test1.Test == 1)

{ // Show Title.

g.setColor (Color.white); // Information.
g.drawString ("Pong!!", 100, 75);
g.drawString ("By: Martin vanPutten.", 100, 90);
g.drawString ("Click ENTER to start game.", 100, 105);

} // End Show Title.

if (Test1.Test == 2)

{ // Don't Show Title.

g.setColor (Color.black);
g.drawString ("Pong!!", 100, 75);
g.drawString ("By: Martin vanPutten.", 100, 90);
g.drawString ("Click ENTER to start game.", 100, 105);

} // End Don't Show Title.

if (Test2.Tests == 1)

{ // Creates Components.

g.setColor (Color.yellow); // Controller Pad.
g.fillRect (x, y, 10, 80);

g.fillRect (xx, yy, 10, 80); // Computer Pad.

g.setColor (Color.blue); // Border.
g.drawRect (0, 0, 799, 499);

g.setColor (Color.blue); // Center Line.
g.drawRect (400, 0, 1, 500);

g.setColor (Color.white); // Ball.
g.fillOval (X, Y, 30, 30);

} // End Creates Components.

if (Test2.Tests == 2)

{ // Ends Game.

g.setColor (Color.black); // Black Screen.
g.fillRect (0, 0, 800, 500);

if (X == 0)

{ // Player Loses.

g.setColor (Color.white);
g2d.setFont (font);
    g2d.setRenderingHint (RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    g2d.drawString ("You Lose!!", 280, 350);
 
} // End Player Loses.

if (X == 770)

{ // Player Wins.

g.setColor (Color.white);
g2d.setFont (font);
    g2d.setRenderingHint (RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    g2d.drawString ("You Win!!", 280, 350);
 
} // End Player Wins.
 
} // End Ends Game.

} // End Graphics.

public class TimeListenerUp implements ActionListener

{ // TimeListenerUp Class.

public void actionPerformed(ActionEvent event)

{ // Repaints Up Movements.

y--; 
repaint ();

} // End Repaints Up Movements.

} // End TimeListenerUp Class.

public class TimeListenerDown implements ActionListener

{ // TimeListenerDown Class.

public void actionPerformed(ActionEvent event)

{ // Repaints Down Movements.

y++; 
repaint ();

} // End Repaints Down Movements.

} // End TimeListenerDown Class.

public class TimeListenerBall implements ActionListener

{ // TimeListenerBall Class.

public void actionPerformed(ActionEvent event)

{ // Repaints Ball Movements.

pTop = Y + 15;
pBottom = Y - 15;

Y++; 
X++;

Y += yIncrement; 
X += xIncrement;

if (Y == 474) // Bounce Ball Up.      
yIncrement += -1;

if (Y == 0)  // Bounce Ball Down.     
yIncrement += 1;

if (X == 759) // Bounce Ball Left. 
xIncrement += -1;

if (X == 10 && pTop >= y && pBottom <= (y + 80)) // Bounce Ball Right.
xIncrement += 1;

if (X == 0 || X == 770) // Game Is Over.

{ // Game Is Over.

timerBall.stop ();
Test2.trials (0, 1);

} // End Game Is Over.

repaint ();

} // End Repaints Ball Movements.

} // End TimeListenerBall Class.

public class TimeListenerAI implements ActionListener

{ // TimeListenerAI Class.

public void actionPerformed(ActionEvent event)

{ // Repaints AI Movements.

yy = Y - 25;

if (Y >= 445) // Stops Down Movement.
yy = 420;
else 
yy--;

if (Y <= 25) // Stops Up Movement.
yy = 0;
else
yy++;

repaint ();

} // End Repaints AI Movements.

} // End TimeListenerAI Class.

} // End Pong Applet.

class Tester
       
    { // Tester Class.
    
    int Test; // Test.

public void trial (int Yes, int No) 
       
    { // Create Test.
    
    if (Yes == 1 && No == 0)
    Test = 1;
    else if (Yes == 0 && No == 1)
Test = 2; 
    
    } // End Create Test.
       
} // End Tester Class.

class Exam
 
{ // Exam Class.

int Tests;

public void trials (int Yah, int Nay)

{ // Create Second Test.

if (Yah == 1 && Nay == 0)
    Tests = 1;
    else if (Yah == 0 && Nay == 1)
Tests = 2;

} // End Create Second Test.

} // End Exam Class.

Swing doublebuffers by default. Have you considered it?

I was just told how to double buffer... I don't know what swing double buffers are.

Originally posted by Martin vanPutten:
I was just told how to double buffer... I don't know what swing double buffers are.

The sweet thing is that you don't have to know anything. It's part of the furniture. Just write the code that renders in a simple manner and if you are using Swing components, they will take care of the double buffering.

Originally posted by Martin vanPutten:
I was just told how to double buffer... I don't know what swing double buffers are.

Where are you using double buffering?

This is an example of how you use it.

Notice that the only thing you have to do to implement double buffering with Applet is override update so it only call paint, and then in paint draw on the offscreen image. After the offscreen image is finished, then display it.

import java.awt.*;
import java.util.*;
import java.applet.*;
 
public class EliminateFlicker extends Applet implements Runnable {
   private Rectangle rectangle;
   private boolean keepGoing;
   private Image offScreenImage;
   private Graphics offScreenGraphics;
 
   public void init() {
      setBackground(Color.white);
 
      keepGoing = true;
 
      new Thread(this).start();
 
      rectangle = new Rectangle(0,getHeight()/2-50,50,50);
 
      offScreenImage = createImage(getWidth(),getHeight());
 
      offScreenGraphics = offScreenImage.getGraphics();
   }
 
   public void paint(Graphics g) {
      offScreenGraphics.clearRect(0,0,getWidth(),getHeight());
 
      offScreenGraphics.setColor(Color.black);
 
      offScreenGraphics.fillRect(rectangle.x,
                                 rectangle.y,
                                 rectangle.width,
                                 rectangle.height);
 
      g.drawImage(offScreenImage,0,0,this);
   }
 
   public void update(Graphics g) {
      paint(g);
   }
 
   private void pause(double seconds) {
      try {
         Thread.sleep((int)(seconds*1000));
      } catch (InterruptedException ie) {
      }
   }
 
   public void run() {
      while (keepGoing) {
         rectangle.x = (rectangle.x + 5) % getWidth();         
 
         pause(0.1);
 
         repaint();
      }
   }
 
}

The sweet thing is that you don't have to know anything. It's part of the furniture. Just write the code that renders in a simple manner and if you are using Swing components, they will take care of the double buffering.

I don't understand.

The sweet thing is that you don't have to know anything. It's part of the furniture. Just write the code that renders in a simple manner and if you are using Swing components, they will take care of the double buffering.

I don't understand.

Do you know about Swing?

no. i'm bad with knowing what exactly with what things do.

Can somebody look through my code and point out the problem... then I could look at it... and try and figure it out?

I was asking if you knew Swing because most Java programmers who have the choice prefer Swing over the AWT. From your answer, although unclear, I assume you don't know Swing. Then I can't help you. I also avoid applets, but that's a story for another time...

So is it possible to fix my problem with what I have now?

Originally posted by Martin vanPutten:
So is it possible to fix my problem with what I have now?

Yes. Digest what Keith wrote. Again, it would be simpler if you knew Swing.

It sounds like you are repainting the screen or background, but not the ball.

You could also try "erasing" the ball.

I considered erasing the graphics after they moved from there previous spots but I don't know how to go about it. Can somebody shed some light?

You are erase a portion of the screen using clearRect

I played with it a little. But I can't figure out how to use the clearOval to erase the previous balls?

import java.applet.Applet; 
import java.awt.*; 
import java.awt.event.*; 
import javax.swing.*;
 
/*//////////////////// 
Pong////////////////// 
Martin vanPutten////// 
Woodstock High School/ 
*/////////////////////  
 
public class Pong extends Applet implements Runnable   
 
{ // Pong Applet.   
 
int x = 1; // Controller Pad Width.
int y = 215; // Controller Pad Length.
int xx = 789; //Computer Pad Width.
int yy = 210; // Computer Pad Length.
int X = 10; // Ball Width.
int Y = 235; // Ball Length.
int pTop; // Center Point Of Ball Hitting Top Of Paddle.
int pBottom; // Center Point Of Ball Hitting Bottom Of Paddle.
int Speed = -200;
int t = 0; // Top Border.
int b = 420; // Bottom Border. 
int yIncrement; // Balls Y-Axis Incrementing. 
int xIncrement; // Balls X-Axis Incrementing. 
 int frame; // Frames.
    int delay; // Delay Time.
    
    Thread animator; // Animator Thread.
    
Timer timerUp; // Timer Up Pad. 
Timer timerDown; // Timer Down Pad. 
Timer timerBall; // Timer Ball. 
Timer timerAI; // Timer AI.

Tester Test1 = new Tester (); // Performs Test Class. 
Exam Test2 = new Exam (); // Performs Exam Class.

public void init ()  
 
{ // Initialize.  
 
 String str = getParameter ("fps"); // Gets Parameters For Double Buffering.
int fps = (str != null) ? Integer.parseInt (str) : 10; // Initializes Integer fps.
delay = (fps > 0) ? (1000 / fps) : 100; // Delay Time.
 
setBackground (Color.black); // Background Color.

timerUp = new Timer (-200, new TimeListenerUp ()); // Pulls TimeListenerUp Class. 
timerDown = new Timer (-200, new TimeListenerDown ()); // Pulls TimeListenerDown Class. 
timerBall = new Timer (Speed, new TimeListenerBall ()); // Pulls TimeListenerBall Class. 
timerAI = new Timer (-200, new TimeListenerAI ()); // Pulls TimeListenerAI Class.

Test1.trial (1, 0); // Test.
Test2.trials (1, 0); // Second Test.

addKeyListener (new KeyAdapter () // Key Listener.  
 
{ // Keys.              
 
public void keyPressed (KeyEvent keP)              
 
{ // Keys Pressed.                  
 
if (keP.getKeyCode () == KeyEvent.VK_ENTER) // Starts Pong.  
 
{ // Starts Components.  
 
timerBall.start (); // Start Ball Component. 
timerAI.start (); // Start AI Component.

Test1.trial (0, 1); // Test.
    repaint ();
       
} //End Starts Components.  
 
if (keP.getKeyCode () == KeyEvent.VK_UP) // Start Up.         
timerUp.start ();          
 
if (keP.getKeyCode () == KeyEvent.VK_DOWN) // Start Down.         
timerDown.start ();

if (y <= t)  
 
{ // Up Restriction.  
 
timerUp.stop (); 
y = 0;  
 
} // End Up Restriction. 
 
if (y >= b)

{ // Down Restriction.

timerDown.stop (); 
y = 420;

} // End Down Restriction.

} // End Keys Pressed.

public void keyReleased (KeyEvent keR)

{ // Keys Released.

if (keR.getKeyCode () == KeyEvent.VK_UP) // Stop Up.         
timerUp.stop ();

if (keR.getKeyCode () == KeyEvent.VK_DOWN) // Stop Down.         
timerDown.stop ();

} // Keys Released.

} // End Keys.

); // End Key Listener.

} // End Initialize.

public void start ()

{ // Starts Animator.

animator = new Thread (this);
animator.start ();
    
    } // End Starts Animator.

public void run ()

{ // Runs Animation.

long tm = System.currentTimeMillis (); // Remembers The Starting Time.
while (Thread.currentThread () == animator)

{ // Creates Animation.
    
    repaint (); // Display The Next Frame Of Animation.
    
    try 
    
    { // Delay Depending On How Far Behind.

tm += delay;

Thread.sleep (Math.max (0, tm - System.currentTimeMillis ()));
    
    } // End Delay Depending On How Far Behind.
    
    catch (InterruptedException e) 
    
    { // Break.

break;
    
    } // End Break.
    
    frame++; // Advance The Frame.

} // End Creates Animation.
    
    } // End Runs Animation.

public void stop ()

{ // Stops Animation.

animator = null;
    
    } // End Stops Animation.
    
public void paint (Graphics g)

{ // Graphics.

Graphics2D g2d = (Graphics2D) g; // 2D Graphics.
    
    int screenRes = Toolkit.getDefaultToolkit ().getScreenResolution (); // Screen Resolution.
    int fontSize = (int) Math.round (40.0 * screenRes / 72.0); // Font Size.
 
    Font font = new Font("Arial", Font.PLAIN, fontSize); // Font Style.

if (Test1.Test == 1)

{ // Show Title.

g.setColor (Color.white); // Information.
g.drawString ("Pong!!", 100, 75);
g.drawString ("By: Martin vanPutten.", 100, 90);
g.drawString ("Click ENTER to start game.", 100, 105);

} // End Show Title.

if (Test1.Test == 2)

{ // Don't Show Title.

g.setColor (Color.black);
g.drawString ("Pong!!", 100, 75);
g.drawString ("By: Martin vanPutten.", 100, 90);
g.drawString ("Click ENTER to start game.", 100, 105);

} // End Don't Show Title.

if (Test2.Tests == 1)

{ // Creates Components.

g.setColor (Color.yellow); // Controller Pad.
g.fillRect (x, y, 10, 80);

g.fillRect (xx, yy, 10, 80); // Computer Pad.

g.setColor (Color.blue); // Border.
g.drawRect (0, 0, 799, 499);

g.setColor (Color.blue); // Center Line.
g.drawRect (400, 0, 1, 500);

g.setColor (Color.white); // Ball.
g.fillOval (X, Y, 30, 30);

} // End Creates Components.

if (Test2.Tests == 2)

{ // Ends Game.

g.setColor (Color.black); // Black Screen.
g.fillRect (0, 0, 800, 500);

if (X == 0)

{ // Player Loses.

g.setColor (Color.white);
g2d.setFont (font);
    g2d.setRenderingHint (RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    g2d.drawString ("You Lose!!", 280, 350);
 
} // End Player Loses.

if (X == 770)

{ // Player Wins.

g.setColor (Color.white);
g2d.setFont (font);
    g2d.setRenderingHint (RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    g2d.drawString ("You Win!!", 280, 350);
 
} // End Player Wins.
 
} // End Ends Game.

} // End Graphics.

public void update (Graphics g)

{ // Updates Existing Graphics.

paint (g);

} // End Updates Existing Graphics.

public class TimeListenerUp implements ActionListener

{ // TimeListenerUp Class.

public void actionPerformed(ActionEvent event)

{ // Repaints Up Movements.

y--; 
repaint ();

} // End Repaints Up Movements.

} // End TimeListenerUp Class.

public class TimeListenerDown implements ActionListener

{ // TimeListenerDown Class.

public void actionPerformed(ActionEvent event)

{ // Repaints Down Movements.

y++; 
repaint ();

} // End Repaints Down Movements.

} // End TimeListenerDown Class.

public class TimeListenerBall implements ActionListener

{ // TimeListenerBall Class.

public void actionPerformed(ActionEvent event)

{ // Repaints Ball Movements.

pTop = Y + 15;
pBottom = Y - 15;

Y++; 
X++;

Y += yIncrement; 
X += xIncrement;

if (Y == 474) // Bounce Ball Up.      
yIncrement += -1;

if (Y == 0)  // Bounce Ball Down.     
yIncrement += 1;

if (X == 759) // Bounce Ball Left. 
xIncrement += -1;

if (X == 10 && pTop >= y && pBottom <= (y + 80)) // Bounce Ball Right.
xIncrement += 1;

if (X == 0 || X == 770) // Game Is Over.

{ // Game Is Over.

timerBall.stop ();
Test2.trials (0, 1);

} // End Game Is Over.

repaint ();

} // End Repaints Ball Movements.

} // End TimeListenerBall Class.

public class TimeListenerAI implements ActionListener

{ // TimeListenerAI Class.

public void actionPerformed(ActionEvent event)

{ // Repaints AI Movements.

yy = Y - 25;

if (Y >= 445) // Stops Down Movement.
yy = 420;
else 
yy--;

if (Y <= 25) // Stops Up Movement.
yy = 0;
else
yy++;

repaint ();

} // End Repaints AI Movements.

} // End TimeListenerAI Class.

} // End Pong Applet.

class Tester
       
    { // Tester Class.
    
    int Test; // Test.

public void trial (int Yes, int No) 
       
    { // Create Test.
    
    if (Yes == 1 && No == 0)
    Test = 1;
    else if (Yes == 0 && No == 1)
Test = 2; 
    
    } // End Create Test.
       
} // End Tester Class.

class Exam
 
{ // Exam Class.

int Tests;

public void trials (int Yah, int Nay)

{ // Create Second Test.

if (Yah == 1 && Nay == 0)
    Tests = 1;
    else if (Yah == 0 && Nay == 1)
Tests = 2;

} // End Create Second Test.

} // End Exam Class.