问答题

程序如下：
∥Java_2. java
import java. awt. *;
import java. awt. event. * ;
public class Java_2 extends Frame{
public Java_2( String s){
super(s);
}
public static void main( String args[ ] ){
Java_2 fr=new Java_2 ("Testing");
Button b=new Button( "Please press me!");
∥********** Found ************
b. addActionListener( (3) );
fr. add(b);
fr. setSize(200,200);
fr. addWindowListener( new WindowAdapter( ){
public void windowClosing( WindowEvent e){
System. exit(0);
}
});
∥********** Found **********
fr. setVisible( (4) );
}
}
class HandleButton implements ActionListener{
public void actionPerformed (ActionEvent e){
System. out. println("The button is pressed!");
}
}