[Java]Double buffering failing to double buffer

Question

Well, as the title says, I am having trouble with double buffering. I read this Java Ebook and it doesn't give you code for what they are teaching you - at least not completely. So I have to do a lot of guess work.

Objective : Bouncing ball in an applet.

It's not working in the way that the ball is still flashing. Aka double buffering is failing to work.

I use three classes, ball class, double buffering class, and MainApplet class. MainApplet extends double buffering, and ball class extends MainApplet

import java.applet.Applet;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Rectangle;

@SuppressWarnings("serial")

public class MainApplet extends DoubleBuffering implements Runnable {

    public Ball ball;
    public Graphics g;

    private Thread ticker;
    public boolean running = false;

    public void init() {

        setSize(100,100);
        ball = new Ball(getWidth() / 5f, getHeight() / 4f, 1.5f,
                2.3f, 12, Color.red);
        moveBall();
    }

    public void run() {
        while(running) {
            try {
                Rectangle bou = new Rectangle(getWidth(), getHeight());
                ball.move(bou);
                ball.update(getGraphics());
                Thread.sleep(1000 / 15);
            } catch (InterruptedException e) {
                System.out.println(e.getMessage());
            }
            repaint();
        }
    }

    public void moveBall() {
        start();
    }

    public synchronized void start() {
        running = true;
        ticker = new Thread(this);
        ticker.setPriority(Thread.MIN_PRIORITY + 1);
        ticker.start();
    }


    public synchronized void stop() {
        running = false;
        ticker.stop();
    }
}


import java.applet.Applet;
import java.awt.Graphics;
import java.awt.Image;

public class DoubleBuffering extends Applet
{
    Image offScreenBuffer;

    @SuppressWarnings("deprecation")
    public void update(Graphics g)
    {
        System.out.println("We are buffing");
        Graphics gr; 
        if (offScreenBuffer==null ||
                (! (offScreenBuffer.getWidth(this) == this.size().width
                        && offScreenBuffer.getHeight(this) == this.size().height)))
        {
            offScreenBuffer = this.createImage(size().width, size().height);
        }
        gr = offScreenBuffer.getGraphics();
        System.out.println("Something else");
        paint(gr); 
        g.drawImage(offScreenBuffer, 0, 0, this);     
    }
}


import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Rectangle;


public class Ball extends MainApplet{

    int size;
    private Color color;
    public float x, y, dx, dy;

    public Ball ball;
    public int width, height;
    public Image offscreenImage;
    public Graphics offscr;
    private MainApplet ma;


    Ball (float x, float y, float dx, float dy, int size,
            Color color) {
        this.x = x;
        this.y = y;
        this.dy = dx;
        this.dy = dy;
        this.color = color;
        this.size = size;

    }

    public void draw (Graphics g) {
        g.setColor(this.color);
        g.fillOval((int) x, (int) y, size, size);
    }

    public void update(Graphics g)  {

        g.clearRect(0, 0, getWidth(), getHeight());
        draw(g);

    }

    public void move(Rectangle bounds) {
        // Add velocity values dx/dy to position to
        // ball s new position
        x += dx;
        y += dy;

        // Check for collision with left edge
        if (x < bounds.x && dx < 0) {
            dx = -dx;
            x -= 2 * (x - bounds.x);
        } 
        // Check for collision with right edge
        else if (x + size >  bounds.x + bounds.width &&
                dx > 0) {
            dx = -dx;
            x -= 2 * ((x + size) - (bounds.x + bounds.width));
        }
        // Checks for collision with top edge
        else if (y < bounds.y && dy < 0) {
            dy = -dy;
            y -= 2 * (y - bounds.y);
        }
        // Checks for collision with bottom edge
        else if (y + size > bounds.y + bounds.height && dy >0) {
            dy = -dy;
            y -= 2 * ((y + size) - (bounds.y + bounds.width));
        }
    }
}  

Note: I'm not too sure how this code will come out >.< it looks as if it's being choppy with the 'code:' function.

Anyways, don't hate too hard on my conventions, I'm still rather new. Tips and answers would be appreciated. Thanks.

Answer 1

Instead of calling Thread.Sleep() try using the swing Timer like this.

private Timer t;

public void moveBall() {
t = new Timer(1000/15, new ActionListener() {

        public void actionPerformed(ActionEvent e) {
             Rectangle bou = new Rectangle(getWidth(), getHeight());
                ball.move(bou);
                ball.update(getGraphics());
                repaint();
        }
    });
    t.start();
}

public void destroy() {
    if(t!=null) t.stop();
    super.destroy();
}

that should help at least a little bit.

Answer 2

I'm assuming the class DoubleBuffering is some tutorial class. I'm guessing it derives from Applet and not JApplet. If you use JApplet you will get double buffering by default.