简单的KeyListener无法正常工作

我正在研究一个非常简单的Java项目，试图了解如何使用KeyListener。
我创建了一个Main类和一个KeyListener，MouseListener类。我想按键盘键时会发生一些事情。到目前为止，唯一可行的是点击时Hello。

I'm working on a really simple project in Java to try to understand how to use KeyListener. I've created a Main class and a KeyListener, MouseListener class. I want to get something to happen when I press a keyboard key. So far the only thing that is working is "Hello" when I click.

这是我的代码：

import javax.swing.JFrame;
import javax.swing.JPanel;

public class KeyPractice{

    public static void main(String[] args) {

        JFrame frame = new JFrame();
        JPanel panel = new JPanel();

        panel.addKeyListener(new KeyEar());
        panel.addMouseListener(new KeyEar());

        frame.add(panel);

        frame.setVisible(true);
        frame.setSize(400, 400);
    } 
}

和Keylistener类....

And the Keylistener class....

import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

public class KeyEar implements KeyListener, MouseListener {

    public KeyEar(){

    }

    @Override
    public void mouseClicked(MouseEvent arg0) {
        System.out.println("Hello");
    }

    @Override
    public void mouseEntered(MouseEvent arg0) {
        // TODO Auto-generated method stub
    }

    @Override
    public void mouseExited(MouseEvent arg0) {
        // TODO Auto-generated method stub
    }

    @Override
    public void mousePressed(MouseEvent arg0) {
        // TODO Auto-generated method stub
    }

    @Override
    public void mouseReleased(MouseEvent arg0) {
        // TODO Auto-generated method stub
    }

    @Override
    public void keyPressed(KeyEvent arg0) {
        System.out.println("Hello");
    }

    @Override
    public void keyReleased(KeyEvent arg0) {
        System.out.println("Hello");
    }

    @Override
    public void keyTyped(KeyEvent arg0) {
        System.out.println("Hello");
    }
}