java中对按钮的事件监听

package awt;
import java.awt.*;
import java.awt.event.*;
public class Monitor implements ActionListener{
public void actionPerformed(ActionEvent e){
System.out.println("A button has benn pressed!");
}
}

package awt;
import java.awt.*;
public class graphy {
public static void   main(String[] args){
Frame f = new Frame("Text!");
Button b = new Button("Bt");
Monitor hr = new Monitor();
b.addActionListener(hr);
f.add(b,BorderLayout.CENTER);
f.pack();
f.setVisible(true);
}
}