Change what keys a Java program thinks are being hit

Question

To keep things short, I want to make a Java applet think that when I hit W, A, S or D I am actually hitting up, down, left, or right respectively.

How would I go about doing this?

I would make a simple little GUI with an activate/deactive button on, but I have no idea how the program would fool the Java applet.

Answer 1

You should be using key bindings.

Essentially, you "bind" a key to an action. For example, if you want to bind the W key and the UP key to the "pressed" action in button, you'd write:

button.getInputMap().put(KeyStroke.getKeyStroke("W"), "pressed");
button.getInputMap().put(KeyStroke.getKeyStroke("UP"), "pressed");

And to define what "pressed" should do, you need to add an action which corresponds to it.

button.getActionMap().put("pressed", changeTextAction);

changeTextAction should be an instance of a class which extends AbstractAction. For example:

public class ChangeTextAction extends AbstractAction
{
    private JButton button;
    private String text;

    public ChangeTextAction(JButton button, String text)
    {
        this.button = button;
        this.text = text;
    }

    @Override
    public void actionPerformed(ActionEvent e)
    {
        button.setText(text);
    }
}

Here's an example of a basic program which allows the user to either click, press W, or press UP to trigger an action which changes its text to "Pressed!":

import javax.swing.*;
import java.awt.event.ActionEvent;

class KeyBindingExample extends JFrame
{
    private JButton button;
    private Action changeTextAction;

    public KeyBindingExample()
    {
        button = new JButton("Not Pressed!");
        changeTextAction = new ChangeTextAction(button, "Pressed!");

        button.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke("W"), "pressed");
        button.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke("UP"), "pressed");

        button.getActionMap().put("pressed", changeTextAction);

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        getContentPane().add(button);
        pack();
        setVisible(true);
    }

    public class ChangeTextAction extends AbstractAction
    {
        private JButton button;
        private String text;

        public ChangeTextAction(JButton button, String text)
        {
            this.button = button;
            this.text = text;
        }

        @Override
        public void actionPerformed(ActionEvent e)
        {
            button.setText(text);
        }
    }

    public static void main(String[] args)
    {
        new KeyBindingExample();
    }
}