Multiplayer pong

Question

Hey everybody,
I'm writing a game for a final project and it is supposed to be a four player "Pong"
I have my keyboard listener working just fine, the problem is that it just accept the input from one key, as soon as another key is pressed the first key stop working
I know everybody says this, but I'm kind of starting with java, and that is the only thing left in my game. I saw something about AWTEventMulticaster but I have no idea how to use it.....
does anyone have a sugestion?
thanks!

Answer 1

The usual way of doing this is to store a flag for each key indicating whether it is currently pressed. Most people use an array of 256 booleans for this task.
When I wrote the following code (a LONG time ago) I didn't know that so I used an ArrayList instead, which seemed to work fine, but maybe is a bit slower. I'm sure you could easily adapt what I've done to use an array if you prefered.import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.util.HashSet;
* Generic Keyboard handler for detecting pressed keys. Keeps a list of all the
* keys currently pressed in a HashSet. Register this KeyListener on the main
* window, then use: KeysDownListener.isDown(key) to see if a particular key is
* pressed. KeysDownListener.anyDown() to see if <i>any </i> key is currently
* pressed.
public class KeysDownListener implements KeyListener {
    static private HashSet keysDown = new HashSet();
     * Returns boolean true if the supplied key value represents a key that is
     * currently pressed.
     * @param key
     *            A valid keycode that could be a pressed key.
    static boolean isDown(int key) {
        return keysDown.contains(new Integer(key));
     * Returns true if the supplied key value is a key that was down when this
     * routine was called, but waits until the key is released before returning.
     * If the key wasn't down on entry, then the routine returns false
     * immediately.
    static boolean wasDown(int key) {
        if (isDown(key)) {
            while (isDown(key)) {
                try {
                    Thread.sleep(5);
                } catch (InterruptedException ie) {
            return true;
        return false;
     * Returns boolean true if there are any keys currently pressed.
    static boolean anyDown() {
        return ! keysDown.isEmpty();
    public void keyPressed(KeyEvent ke) {
        keysDown.add(new Integer(ke.getKeyCode()));
    public void keyReleased(KeyEvent ke) {
        keysDown.remove(new Integer(ke.getKeyCode()));
    public void keyTyped(KeyEvent ke) {
}I add the listener to the panel like this:
qixFrame.addKeyListener(new KeysDownListener());And I use the results like this:        if (KeysDownListener.isDown(KeyEvent.VK_UP)) {
            moveX = 0;
            moveY = - 1;
        } else if (KeysDownListener.isDown(KeyEvent.VK_DOWN)) {
            moveX = 0;
            moveY = + 1;
        ...Looking at this code now, I find it quite weird that I instantiate the class, but then use static methods - I'm sure this code could be improved on! :-)
Regards,
Tim