Keylisteners in games

Hey guys,
I'm trying to create a simple game using Java2D. I have a JPanel inside a JFrame, and I register the JPanel with a KeyListener. Then I implement the KeyPressed method for the left and right arrow keys, so I can move my character around.
However, when I press and hold the left arrow key for example, the character moves one space, then pauses for a little bit, then moves continuously. That is great for text editing (see how it works when you are writing some text - press and hold any key, and see how it performs a singe action, waits a moment, then repeats). But this is unacceptable in a game.
How do I stop this from happening?

Use keypressed and keyreleased an your own timer

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Please help with KeyListeners!!!!!

Hi...
I am trying to make the Snake game. I am working with keyListeners...I have never worked with keylisteners. So this is what I have to activate my left arrow key....
public void keyPressed(KeyEvent e) {
int key = e.getKeyCode();
snakeLeft = theSnake.getXPosition();
System.out.println(snakeLeft);
if(key == KeyEvent.VK_ESCAPE ){
     System.exit(0);
else if(key == e.VK_LEFT){
     snakeLeft -= 8;
     if(snakeLeft < 3){
     snakeLeft = 3;
     theSnakeLife.moveLeft(snakeLeft);
     redisplay();
theSnake is an object of the Snake class (that where I have the x and y positions) System.out.println(snakeLeft)...I was trying to see if the SnakeLeft prints the xPosition...but it does not.
Thank you...
srj6

By using this sample, you can control the speed of the snake, and the movement is smoother.
import java.awt.*;
import java.awt.event.*;
public class Snake extends Frame
     DPanel pan = new DPanel();
public Snake()
     super();
     setBounds(1,1,500,325);
     addWindowListener(new WindowAdapter()
     {     public void windowClosing(WindowEvent ev)
               dispose();
               System.exit(0);
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     setVisible(true);
     Thread th = new Thread(pan);
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public class DPanel extends Panel implements KeyListener, Runnable
     Rectangle snak = new Rectangle(10,10,70,5);
     int       mx   = 0;
     Graphics og;
public DPanel()
     super();
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public void run()
     while (true)
          try
               Thread.sleep(4);
               if (mx < 0)
                    og.setColor(Color.pink);
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               if (mx > 0)
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               if (mx != 0)
                    snak.x = snak.x + mx;
                    og.setColor(Color.black);
                    og.fillRect(snak.x,snak.y,snak.width,snak.height);
          catch(InterruptedException ie){}
public void paint(Graphics g)
     if (og == null) og = getGraphics();
     g.setColor(Color.black);
     g.fillRect(snak.x,snak.y,snak.width,snak.height);
public void keyTyped(KeyEvent e){}
public void keyPressed(KeyEvent e)
     if (e.getKeyCode() == KeyEvent.VK_RIGHT) mx = 1;
     if (e.getKeyCode() == KeyEvent.VK_LEFT) mx = -1;
public void keyReleased(KeyEvent e)
     if (e.getKeyCode() == KeyEvent.VK_RIGHT) mx = 0;
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public static void main (String[] args)
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}       Noah

KeyListener, sound problems with game

Hi All!
I'm new to gaming.. I've developed a game called Puyo Puyo using Swings. But its got some problems...
My game plays well for the first time but doesn't restart.
Im unable to implement keyListeners.. they simply dont work..
Can someone tell me how to add sounds to my game?
When executed, a blank window appears first, then on maximising.. evrything else comes into picture.. how do i rectify this? Please help me out at the earliest wid all ur possible and favourable hints n replies..
Take Care ya'll!

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I want to repaint the canvas panel in this bouncing balls game, but i do something wrong i don't know what, and the JPanel doesn't repaint?
The first class defines a BALL as a THREAD
If anyone knows how to correct the code please to write....
package fuck;
//THE FIRST CLASS
class CollideBall extends Thread{
    int width, height;
    public static final int diameter=15;
    //coordinates and value of increment
    double x, y, xinc, yinc, coll_x, coll_y;
    boolean collide;
    Color color;
    Rectangle r;
    bold BouncingBalls balls; //A REFERENCE TO SECOND CLASS
    //the constructor
    public CollideBall(int w, int h, int x, int y, double xinc, double yinc, Color c, BouncingBalls balls) {
        width=w;
        height=h;
        this.x=x;
        this.y=y;
        this.xinc=xinc;
        this.yinc=yinc;
        this.balls=balls;
        color=c;
        r=new Rectangle(150,80,130,90);
    public double getCenterX() {return x+diameter/2;}
    public double getCenterY() {return y+diameter/2;}
    public void move() {
        if (collide) {
        x+=xinc;
        y+=yinc;
        //when the ball bumps against a boundary, it bounces off
        //bounce off the obstacle
    public void hit(CollideBall b) {
        if(!collide) {
            coll_x=b.getCenterX();
            coll_y=b.getCenterY();
            collide=true;
    public void paint(Graphics gr) {
        Graphics g = gr;
        g.setColor(color);
        //the coordinates in fillOval have to be int, so we cast
        //explicitly from double to int
        g.fillOval((int)x,(int)y,diameter,diameter);
        g.setColor(Color.white);
        g.drawArc((int)x,(int)y,diameter,diameter,45,180);
        g.setColor(Color.darkGray);
        g.drawArc((int)x,(int)y,diameter,diameter,225,180);
        g.dispose(); ////////
    ///// Here is the buggy code/////
    public void run() {
        while(true) {
            try {Thread.sleep(15);} catch (Exception e) { }
            synchronized(balls)
                move();
                balls.repairCollisions(this);
            paint(balls.gBuffer);
            balls.canvas.repaint();
//THE SECOND CLASS
public class BouncingBalls extends JFrame{
    public Graphics gBuffer;
    public BufferedImage buffer;
    private Obstacle o;
    private List<CollideBall> balls=new ArrayList();
    private static final int SPEED_MIN = 0;
    private static final int SPEED_MAX = 15;
    private static final int SPEED_INIT = 3;
    private static final int INIT_X = 30;
    private static final int INIT_Y = 30;
    private JSlider slider;
    private ChangeListener listener;
    private MouseListener mlistener;
    private int speedToSet = SPEED_INIT;
    public JPanel canvas;
    private JPanel p;
    public BouncingBalls() {
        super("fuck");
        setSize(800, 600);
        p = new JPanel();
        Container contentPane = getContentPane();
        final BouncingBalls xxxx=this;
        o=new Obstacle(150,80,130,90);
        buffer=new BufferedImage(getSize().width, getSize().height, BufferedImage.TYPE_INT_RGB);
        gBuffer=buffer.getGraphics();
        //JPanel canvas start
        final JPanel canvas = new JPanel() {
            final int w=getSize().width-5;
            final int h=getSize().height-5;
            @Override
            public void update(Graphics g)
               paintComponent(g);
            @Override
            public void paintComponent(Graphics g) {
                super.paintComponent(g);
                gBuffer.setColor(Color.ORANGE);
                gBuffer.fillRect(0,0,getSize().width,getSize().height);
                gBuffer.draw3DRect(5,5,getSize().width-10,getSize().height-10,false);
                //paint the obstacle rectangle
                o.paint(gBuffer);
                g.drawImage(buffer,0,0, null);
                //gBuffer.dispose();
        };//JPanel canvas end
        addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent e) {
                System.exit(0);
        addButton(p, "Start", new ActionListener() {
            public void actionPerformed(ActionEvent evt) {
                CollideBall b = new CollideBall(canvas.getSize().width,canvas.getSize().height
                        ,INIT_X,INIT_Y,speedToSet,speedToSet,Color.BLUE,xxxx);
                balls.add(b);
                b.start();
        contentPane.add(canvas, "Center");
        contentPane.add(p, "South");
    public void addButton(Container c, String title, ActionListener a) {
        JButton b = new JButton(title);
        c.add(b);
        b.addActionListener(a);
    public boolean collide(CollideBall b1, CollideBall b2) {
        double wx=b1.getCenterX()-b2.getCenterX();
        double wy=b1.getCenterY()-b2.getCenterY();
        //we calculate the distance between the centers two
        //colliding balls (theorem of Pythagoras)
        double distance=Math.sqrt(wx*wx+wy*wy);
        if(distance<b1.diameter)
            return true;
        return false;
    synchronized void repairCollisions(CollideBall a) {
        for (CollideBall x:balls) if (x!=a && collide(x,a)) {
            x.hit(a);
            a.hit(x);
    public static void main(String[] args) {
        JFrame frame = new BouncingBalls();
        frame.setVisible(true);
} And when i press start button:
Exception in thread "Thread-2" java.lang.NullPointerException
at fuck.CollideBall.run(CollideBall.java:153)
Exception in thread "Thread-3" java.lang.NullPointerException
at fuck.CollideBall.run(CollideBall.java:153)
Exception in thread "Thread-4" java.lang.NullPointerException
at fuck.CollideBall.run(CollideBall.java:153)
and line 153 is: balls.canvas.repaint(); in Method run() in First class.
Please help.

public RepaintManager manager;
public BouncingBalls() {
        manager = new RepaintManager();
        manager.addDirtyRegion(canvas, 0, 0,canvas.getSize().width, canvas.getSize().height);
    public void run() {
        while(true) {
            try {Thread.sleep(15);} catch (Exception e) { }
            synchronized(balls)
                move();
                balls.repairCollisions(this);
            paint(balls.gBuffer);
            balls.manager.paintDirtyRegions(); //////// line 153
   but when push start:
Exception in thread "Thread-2" java.lang.IllegalMonitorStateException
at java.lang.Object.notifyAll(Native Method)
at fuck.CollideBall.run(CollideBall.java:153)
Exception in thread "Thread-3" java.lang.IllegalMonitorStateException
at java.lang.Object.notifyAll(Native Method)
at fuck.CollideBall.run(CollideBall.java:153)
i'm newbie with Concurrency and i cant handle this exceptons.
Is this the right way to do repaint?

Balls don't move in bouncing balls game.Please Help !?

I want to repaint the canvas panel in this bouncing balls game, but i do something wrong i don't know what, and the JPanel doesn't repaint?
The first class defines a BALL as a THREAD
If anyone knows how to correct the code please to write....
package ****;
//THE FIRST CLASS
class CollideBall extends Thread{
    int width, height;
    public static final int diameter=15;
    //coordinates and value of increment
    double x, y, xinc, yinc, coll_x, coll_y;
    boolean collide;
    Color color;
    Rectangle r;
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        this.x=x;
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        this.xinc=xinc;
        this.yinc=yinc;
        this.balls=balls;
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        r=new Rectangle(150,80,130,90);
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    public double getCenterY() {return y+diameter/2;}
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        x+=xinc;
        y+=yinc;
        //when the ball bumps against a boundary, it bounces off
        //bounce off the obstacle
    public void hit(CollideBall b) {
        if(!collide) {
            coll_x=b.getCenterX();
            coll_y=b.getCenterY();
            collide=true;
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        Graphics g = gr;
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        //the coordinates in fillOval have to be int, so we cast
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        while(true) {
            try {Thread.sleep(15);} catch (Exception e) { }
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    public Graphics gBuffer;
    public BufferedImage buffer;
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    private static final int SPEED_MAX = 15;
    private static final int SPEED_INIT = 3;
    private static final int INIT_X = 30;
    private static final int INIT_Y = 30;
    private JSlider slider;
    private ChangeListener listener;
    private MouseListener mlistener;
    private int speedToSet = SPEED_INIT;
    public JPanel canvas;
    private JPanel p;
    public BouncingBalls() {
        super("****");
        setSize(800, 600);
        p = new JPanel();
        Container contentPane = getContentPane();
        final BouncingBalls xxxx=this;
        o=new Obstacle(150,80,130,90);
        buffer=new BufferedImage(getSize().width, getSize().height, BufferedImage.TYPE_INT_RGB);
        gBuffer=buffer.getGraphics();
        //JPanel canvas start
        canvas = new JPanel() {
            final int w=getSize().width-5;
            final int h=getSize().height-5;
            @Override
            public void update(Graphics g)
               paintComponent(g);
            @Override
            public void paintComponent(Graphics g) {
                super.paintComponent(g);
                gBuffer.setColor(Color.ORANGE);
                gBuffer.fillRect(0,0,getSize().width,getSize().height);
                gBuffer.draw3DRect(5,5,getSize().width-10,getSize().height-10,false);
                //paint the obstacle rectangle
                o.paint(gBuffer);
                g.drawImage(buffer,0,0, null);
                //gBuffer.dispose();
        };//JPanel canvas end
        addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent e) {
                System.exit(0);
        addButton(p, "Start", new ActionListener() {
            public void actionPerformed(ActionEvent evt) {
                CollideBall b = new CollideBall(canvas.getSize().width,canvas.getSize().height
                        ,INIT_X,INIT_Y,speedToSet,speedToSet,Color.BLUE,xxxx);
                balls.add(b);
                b.start();
        contentPane.add(canvas, "Center");
        contentPane.add(p, "South");
    public void addButton(Container c, String title, ActionListener a) {
        JButton b = new JButton(title);
        c.add(b);
        b.addActionListener(a);
    public boolean collide(CollideBall b1, CollideBall b2) {
        double wx=b1.getCenterX()-b2.getCenterX();
        double wy=b1.getCenterY()-b2.getCenterY();
        //we calculate the distance between the centers two
        //colliding balls (theorem of Pythagoras)
        double distance=Math.sqrt(wx*wx+wy*wy);
        if(distance<b1.diameter)
            return true;
        return false;
    synchronized void repairCollisions(CollideBall a) {
        for (CollideBall x:balls) if (x!=a && collide(x,a)) {
            x.hit(a);
            a.hit(x);
    public static void main(String[] args) {
        JFrame frame = new BouncingBalls();
        frame.setVisible(true);
} This code draws only the first position of the ball:
http://img267.imageshack.us/my.php?image=51649094by6.jpg

I'm trying to draw everything first to a buffer:
buffer=new BufferedImage(getSize().width, getSize().height, BufferedImage.TYPE_INT_RGB);
gBuffer=buffer.getGraphics();
The buffer is for one JPanel and then i want to draw this buffer every time when balls change their possitions(collide or just move).
The logic is something like this:
startButton -> (ball.start() and add ball to List<balls>),
ball.start() -> ball.run() -> (move allballs, paint to buffer and show buffer)
In the first class:
BouncingBalls balls; //A REFERENCE TO SECOND CLASS
In the second class:
private List<CollideBall> balls=new ArrayList();
the tames are the same but this isn't an error.
Edited by: vigour on Feb 14, 2008 7:57 AM

Game and Ball Hit problem

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if(x_pos - 100 < 2 & y_pos - 100 < 2 || 100-x_pos < 2 && 100 - y_pos < 2)
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slenpree wrote:
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Jonny
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