问答题

本程序的功能是监听键盘敲击事件，并将敲击的字符显示在标签上。起始，文字标签提示“Please press your keyboard!”，当你按下键盘上的字符键时，文字标签就变为“"X"ispressed!”(X代表用户按下的键所代表的字符)，如图所示。

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class exam_27 extends Frame ______{
public static void main(String args[]){
exam_27 f=new exam_27("exam_27");
Panel pan=new Panel();
f.init();
}
public exam_27(String str){
super(str);
}
public void init(){
addWindowListener (new WindowAdapter(){
public void windowClosing(WindowEvent e){
System.exit(0);
}
});
setSize(200,200);
setLayout(new FlowLayout());
lab=new Label("Please press your keyboard!");
add(lab);
addKeyListener(this);
setVisible(true);
}
public void keyTyped(KeyEvent e){
lab.setText("""+______+"" is pressed!");
repaint();
}
public void keyPressed(KeyEvent e){
}
public void keyReleased(KeyEvent e) {
}
private Label lab;
}