How can I simultaneity run blocks of code with key bindings?

Question

I am currently learning how to use key bindings. I was toying with the code I wrote, and I noticed when I press two keys (arrow keys), only the last one would run. Should I simply use KeyListener or is there a way to make this work? Since its a game, it would have to be able to run over 4 keys at the same time.

package game;


import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.awt.image.BufferStrategy;
import java.awt.image.BufferedImage;
import java.awt.image.DataBufferInt;

import javax.swing.AbstractAction;
import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.KeyStroke;

import game.sfx.Screen;
import game.sfx.SpriteSheet;

public class Game implements Runnable{


    private static final long serialVersionUID = 1L;

    public static final int WIDTH = 160;
    public static final int HEIGHT = WIDTH / 12 * 9;
    public static final int SCALE = 3;
    public static final String NAME = "Game";

    private JFrame frame;
    private JPanel panel;

    public boolean running = false;
    public int tickCount = 0;

    private BufferedImage image = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
    private int[] pixels = ((DataBufferInt) image.getRaster().getDataBuffer()).getData();

    Screen screen;

    public Game(){
        panel = new JPanel();

        panel.setMinimumSize(new Dimension(WIDTH*SCALE, HEIGHT*SCALE));
        panel.setMaximumSize(new Dimension(WIDTH*SCALE, HEIGHT*SCALE));
        panel.setPreferredSize(new Dimension(WIDTH*SCALE, HEIGHT*SCALE));

        frame = new JFrame(NAME);

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLayout(new BorderLayout());

        frame.add(panel, BorderLayout.CENTER);
        frame.pack();

        frame.setResizable(false);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true); 

        InputMap im = panel.getInputMap(JPanel.WHEN_IN_FOCUSED_WINDOW); // key binding here
        ActionMap am = panel.getActionMap();

        im.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0), "r");
        am.put("r", new InputHandler("right", this));
        im.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0), "l");
        am.put("l", new InputHandler("left", this));    
        im.put(KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0), "u");
        am.put("u", new InputHandler("up", this));  
        im.put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0), "d");
        am.put("d", new InputHandler("down", this));    

    }


    public void init(){
        screen = new Screen(WIDTH, HEIGHT, new SpriteSheet("res/Untitled.png"));
    }

    public synchronized void start() {
        running = true;
        new Thread(this).start();
    }

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

    public void run() {     
        long lastTime = System.nanoTime();
        double nsPerTick = 1000000000D/60D;

        int frames = 0;
        int ticks = 0;

        long lastTimer = System.currentTimeMillis();
        double delta = 0;

        init();

        while (running){
            long now = System.nanoTime();
            delta += (now - lastTime) / nsPerTick;
            lastTime = now;
            boolean shouldRender = true;
            while(delta >= 1)
            {
                ticks++;
                tick();
                delta -= 1;
                shouldRender = true;
            }

            try {
                Thread.sleep(2);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            if (shouldRender)
            {
                frames++;
                render();
            }

            if(System.currentTimeMillis() - lastTimer >= 1000){
                lastTimer += 1000;
                System.out.println(ticks + " ticks, " + frames + " frames");
                frames = 0;
                ticks = 0;
            }
        }
    }

    public void tick(){
        tickCount++;


    }

    public void render(){


        screen.render(pixels, 0, WIDTH);

        Graphics g = panel.getGraphics();

        g.drawImage(image, 0, 0, panel.getWidth(), panel.getHeight(), null);

        g.dispose();

    }

    public static void main(String[] args){ 
        new Game().start();     
    }

}

class InputHandler extends AbstractAction {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private String key;
    private Game game;


    public InputHandler(String key, Game game) {
        this.key = key;
        this.game = game;
    }


    @Override
    public void actionPerformed(ActionEvent e) {        
        switch(key){
        case "right": 
        game.screen.xOffset+=2;
        break;
        case "left": 
        game.screen.xOffset-=2;
        break;
        case "up": 
        game.screen.yOffset+=2;
        break;
        case "down": 
        game.screen.yOffset-=2;
        break;
        }

    }

}

This is the code

Answer 1

and I noticed when I press two keys (arrow keys), only the last one would run

Because only events are generated for the last key pressed

Should I simply use KeyListener

This is true whether you use a KeyListener or KeyBindings. Its the OS that generates the event.

Since its a game, it would have to be able to run over 4 keys at the same time.

So the solution is to track each key as it is pressed/released

Check out Motion Using the Keyboard . The KeyboardAnimation example shows how this can be done with KeyBindings.

Answer 2

Do what I recommend in my linked to answer :

• Create a game loop using a Swing Timer
• Create an enum called Direction that has UP, DOWN, LEFT, and RIGHT items
• And that also has int vector fields that indicate actual direction
• Create a HashMap<Direction, Boolean> that is changed when an arrow key is pressed
• Have the game loop pole this map, and alter direction depending on which direction is mapped to Boolean.TRUE.
• Set up your Key Bindings to simply change the state of the HashMap, and that's it.