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

public class KeyBoardTest extends JFrame {

public KeyBoardTest(){
super("Try");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setSize(200,200);
Container cp = getContentPane();
cp.setLayout(new BorderLayout());
//JPanel a = new PanelA();
JPanel b = new PanelB();
//cp.add(a,BorderLayout.NORTH);
cp.add(b,BorderLayout.CENTER);
b.setFocusable(true);

setVisible(true);
}
public static void main(String[] args) {
new KeyBoardTest();

}
}
class PanelA extends JPanel{
public PanelA(){
setLayout(new FlowLayout());
add(new JButton("PanelA"));
}
}
class PanelB extends JPanel implements KeyListener{
public PanelB(){
addKeyListener(this);
}
public void keyPressed(KeyEvent e){
System.out.println("KeyEvent");
}
public void keyReleased(KeyEvent e){
}
public void keyTyped(KeyEvent e){
}
}
这段代码，可以实现键盘监听功能！
但是，如果我把注释了的两行代码加进去，为什么就不能实现键盘监听功能了啊
哥哥姐姐，帮帮小弟。谢了

具体的不清楚，但为什么要为面板添加键盘监听啊……如果在PanelB里加上一个JTextField就没问题了，难道是焦点的问题？
添加了一个文本框后：

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

public class KeyBoardTest extends JFrame {

public KeyBoardTest(){
super("Try");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setSize(200,200);
Container cp = getContentPane();
cp.setLayout(new BorderLayout());
JPanel a = new PanelA();
JPanel b = new PanelB();
cp.add(a,BorderLayout.NORTH);
cp.add(b,BorderLayout.CENTER);
b.setFocusable(true);

setVisible(true);
}
public static void main(String[] args) {
new KeyBoardTest();

}
}
class PanelA extends JPanel{
public PanelA(){
setLayout(new FlowLayout());
add(new JButton("PanelA"));
}
}
class PanelB extends JPanel implements KeyListener{
JTextField text;
public PanelB(){
text = new JTextField(10);
text.addKeyListener(this);
add(text);
}
public void keyPressed(KeyEvent e){
System.out.println("KeyEvent");
}
public void keyReleased(KeyEvent e){
}
public void keyTyped(KeyEvent e){
}
}