addKeyListener() doesn't work for JPanel

Question

I am trying to make a game engine. I have made the Game class but the error resides in the KeyBoard class. Here I leave some code.

Class:: Game

package transfer2pc.co.cc.game.tileengine;

import java.awt.Graphics;
import java.util.HashMap;

import javax.swing.JPanel;

import transfer2pc.co.cc.game.tileengine.input.KeyBoard;

public abstract class Game extends JPanel implements Runnable {

   /**
    * 
    */
    private static final long serialVersionUID = 640206679500196209L;

    HashMap<String, ?> maps = null;

    KeyBoard keyBoard = null;

    public Game(){
        super();
        keyBoard = new KeyBoard(this);
        setKeyBoard(keyBoard);
        Thread th = new Thread(this);
        th.start();
    }

    public void run(){
        while(true){
            repaint();
            try {
                Thread.sleep(30);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    @Override
    public void paint(Graphics g){

    }

    public void addMap(){

    }

    public void setMap(){

    }

    public abstract void keyPressed(int code);

    public abstract void keyReleased(int code);

    public abstract void keyTyped(int code);

    public void setKeyBoard(KeyBoard key){
        addKeyListener(key);
    }

}

Class:: KeyBoard

package transfer2pc.co.cc.game.tileengine.input;

import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import transfer2pc.co.cc.game.tileengine.Game;

public class KeyBoard extends KeyAdapter implements KeyListener {

    Game game = null;

    public KeyBoard(Game gm){
        this.game = gm;
    }

    @Override
    public void keyPressed(KeyEvent e) {
        System.out.println("KeyPressed");
        game.keyPressed(e.getKeyCode());
    }

    @Override
    public void keyReleased(KeyEvent e) {
        game.keyReleased(e.getKeyCode());
    }

    @Override
    public void keyTyped(KeyEvent e) {
        game.keyTyped(e.getKeyCode());
    }

    public static char getChar(int key){
        return (char)key;
    }

}

Class:: KeyTest

package transfer2pc.co.cc.game.tileengine.test;

import java.awt.Graphics;

import javax.swing.JFrame;

import transfer2pc.co.cc.game.tileengine.Game;
import transfer2pc.co.cc.game.tileengine.input.KeyBoard;

public class KeyTest extends Game {

    /**
     * 
     */
    private static final long serialVersionUID = 8557676950779023327L;

    char pressed;

    public KeyTest(){
        super();
        addKeyListener(new KeyBoard(this));
    }

    @Override
    public void keyPressed(int code) {
        pressed = KeyBoard.getChar(code);
    }


    @Override
    public void keyReleased(int code) {

    }


    @Override
    public void keyTyped(int code) {

    }

    @Override
    public void paint(Graphics g){
        g.drawString("You pressed: "+pressed, 20, 20);
    }

    public static void main(String[] args){
        JFrame frame = new JFrame("KeyTest");
        frame.setSize(640, 480);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationRelativeTo(null);
        frame.add(new KeyTest());
        frame.setVisible(true);
    }

}

But the error was there was no exception thrown and the input isn't being read. Could anybody say me the correct way of doing this..

Answer 1

Simply, your panel needs to be focusable. Add in wherever you create the panel:

panel.setFocusable(true);
panel.requestFocusInWindow();

Here's a SSCCE (I suggest asking questions with one of these in the future):

import java.awt.Dimension;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class SimpleKeyTest {

    public static void main(String[] args) {

        Runnable r = new Runnable() {

            @Override
            public void run() {
                JFrame frame = new JFrame();
                JPanel panel = new JPanel();

                frame.getContentPane().add(panel);

                panel.addKeyListener(new KeyListener() {

                    @Override
                    public void keyTyped(KeyEvent e) {}

                    @Override
                    public void keyReleased(KeyEvent e) {}

                    @Override
                    public void keyPressed(KeyEvent e) {
                        System.out.println("Pressed " + e.getKeyChar());
                    }
                });

                panel.setFocusable(true);
                panel.requestFocusInWindow();

                frame.setSize(new Dimension(300, 300));
                frame.setVisible(true);
            }

        };

        SwingUtilities.invokeLater(r);

    }
}

Also, https://www.google.com/search?q=jpanel+keylistener

Answer 2

You can add the key listener to the JFrame, that's something I've done in the past. It's probably not a good idea however if you have other components in the JFrame.