为什么我的Java程序不会使用KeyListener确认任何击键？

Question

我完全不知道为什么我的程序没有识别键盘输入.我在整个程序中放置了print语句来确定问题,并且我已经确定keyPressed方法永远不会激活.这是我为一个课程项目制作的游戏,是的,我是一个相对初学的程序员.提前致谢!(以下代码)

import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.ImageIcon;
import javax.swing.JApplet;


public class Dodger extends JApplet implements Runnable, KeyListener {

Thread myThread;

public Image bg;
public Image pic;
public boolean loaded;

public int cx, cy, speed, x, y;

public void init(){
    setSize(800,800);
    loaded = false;
    x = 2;
    y = 400;
    cx = 0;
    cy = 0;
    speed = 3;
    myThread = new Thread(this);
    myThread.start();
    addKeyListener(this);
}

public void run(){
    loadpic();
    repaint();
    while (myThread!=null)
    {

        try{
            myThread.sleep(18);
        }catch(InterruptedException e){
            e.printStackTrace();
        }
        repaint();
    }
}

public void upMotion(){
    cy = cy + speed;
}

public void downMotion(){
    cy = cy - speed;    
}

public void leftMotion(){
    cx = cx - speed;
}

public void rightMotion(){
    cx = cx + speed;
}

@Override
public void keyPressed(KeyEvent k) {

    if (k.getKeyCode() == KeyEvent.VK_LEFT) {
        System.out.println("work");
        leftMotion();
    }

    if (k.getKeyCode() == KeyEvent.VK_RIGHT) {
        rightMotion();
    }

    if (k.getKeyCode() == KeyEvent.VK_UP) {
        upMotion();
    }

    if (k.getKeyCode() == KeyEvent.VK_DOWN) {
        downMotion();
    }
}

@Override
public void keyReleased(KeyEvent e) {
}

@Override
public void keyTyped(KeyEvent e) {
}

public void loadpic(){
    bg = new ImageIcon(getClass().getResource("back.png")).getImage();
    pic = new ImageIcon(getClass().getResource("smile.png")).getImage();
    loaded = true;
    repaint();
}



public void paint(Graphics g){
    g.drawImage(bg, 0, 0, this);
    g.drawImage(pic, cx, cy, this);
}   
}

Answer 1

当applet可聚焦并具有焦点时,可以检测到关键事件.管理焦点一直是applet的问题.问题主要在于Sun从不打算指定应该理想地应用于可聚焦HTML元素和applet的混合页面的焦点行为.

根据汤姆的建议,添加到最后 init()

setFocusable(true);

为了安全起见,还要覆盖:

public void start() {
    this.requestFocusInWindow();
}

顺便说一句,通常最好在Swing中使用键绑定.他们还要求applet具有输入焦点.