键盘输入无效

Question

我无法从键盘获得任何输入，我不知道为什么。请更正我的代码以使其正常工作。

在我的程序中，我创建了一个扩展JFrame的Window，然后我创建了扩展JPanel的Panel，然后我将Panel添加到了我的Window。 Panel实现了KeyListener，并且还具有请求的焦点。

这是我的主要课程：

package dev.thomaslienbacher.spacefighter;

import java.awt.Image;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;

import javax.swing.Timer;

public class Main {

    public static Window window;
    public static Panel panel;
    public static int width = 0;
    public static int height = 0;
    public static final int FPS = 35;

    public static void main(String[] args) {
        panel = new Panel(FRAMEWIDTH, FRAMEHEIGHT);

        ArrayList<Image> icons = new ArrayList<Image>();
        icons.add(Utils.getImage("res/icon8.png"));

        gameMechanics = new GameMechanics();
        window = new Window(title, 606, 700, icons);
        window.add(panel);
        width = window.getContentPane().getSize().width;
        height = window.getContentPane().getSize().height;

        Timer gameLoopTimer = new Timer(1000 / FPS, new ActionListener(){
            @Override
            public void actionPerformed(ActionEvent e) {
                panel.repaint();
                panel.actionPerformed(null);
            }}
        );
        gameLoopTimer.start();
    }
}

这是我的Window类：

package dev.thomaslienbacher.spacefighter;

import java.util.ArrayList;

import javax.swing.JFrame;

public class Window extends JFrame{

    public Window(String title, int width, int height, ArrayList<Image> icons){
        super(title);

        this.setFocusable(true);
        this.setSize(width, height);
        this.setLocationRelativeTo(null);
        this.setVisible(true);  
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setResizable(false);
        this.setIconImages(icons);
        this.setCursor(cross);
    }
}

这是我的Panel类：

package dev.thomaslienbacher.spacefighter;


import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.JPanel;

public class Panel extends JPanel implements ActionListener, KeyListener{

    public Panel(int width, int height) {
        this.setBackground(Color.BLACK);
        this.setFocusable(true);
        this.addKeyListener(this);
        this.setBounds(0, 0, width, height);
        this.requestFocusInWindow();
        this.requestFocus();
    }

    @Override
    public void paint(Graphics g) {
        super.paint(g);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
    }

    @Override
    public void keyPressed(KeyEvent e) {
    }

    @Override
    public void keyReleased(KeyEvent e) {
        System.out.println("Released");
    }

    @Override
    public void keyTyped(KeyEvent e) {

    }
}