问答题

本程序监听鼠标用窗口的进出和点击情况，并将这些信息打印出来。当输入移进窗口后台就打印出“Entered”，当鼠标移出窗口，后台就打印出“Exited”，当鼠标按下时，后台就打印出“Pressed”，当鼠标松开时，后台就打印出“Released”和“Clicked”。
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class exam_26 extends Frame ______{
public static void main (String args[]){
exam_26 f=new exam_26("exam_26");
Panel pan=new Panel();
f.init();
}
public exam_26(String str){
super(str);
}
public void init(){
addWindowListener (new WindowAdapter(){
public void windowClosing(WindowEvent e){
System.exit(0);
}
});
setSize(200,200);
setLayout (new FlowLayout());
______;
setVisible(true);
}
public void mouseClicked(MouseEvent e){
System.out.println("Clicked");
}
public void mousePressed(MouseEvent e){
System.out.println("Pressed");
}
public void mouseReleased(MouseEvent e){
System.out.println("Released");
}
public void mouseEntered(MouseEvent e){
System.out.println("Entered");
}
public void mouseExited(MouseEvent e){
System.out.println("Exited");
}
}