你如何使用keylistener？

Question

It seems I can't make my program to notice the fact that I'm pressing a button. I've seen at a lot of tutorials and images and I think this code should work but it just won't. Can anybody help me?

 package projekt;

import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Random;

public class Projekt extends javax.swing.JFrame implements KeyListener {


public Projekt() {
    initComponents();
    this.addKeyListener(this);
}

 [...]

@SuppressWarnings("unchecked")

@Override
public void keyPressed(KeyEvent e) {
    if (e.getKeyCode() == KeyEvent.VK_A){
        System.out.println("It works!!!"); //It won't print this
}


@Override
public void keyTyped(KeyEvent e) {
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
}

@Override
public void keyReleased(KeyEvent e) {
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
}
}

Answer 1

A KeyEvent is only dispatch to the component that has focus.

this.addKeyListener(this);

You are adding the KeyListener to the frame. The frame does not have focus. A component displayed on the frame has focus.

I can't seem to get my program to pick up the fact that I'm pressing a button.

You should not be using a KeyListener to listen for specific key events. That is old AWT code.

In Swing you should be using Key Bindings . Key Bindings will allow you to listen for a KeyStroke even if the component doesn't have focus.

Read the section from the Swing tutorial on How to Use Key Bindings for more information.