java监听器

import java.awt.BorderLayout;
import java.awt.Button;
import java.awt.Frame;
import java.awt.TextField;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;

class Max extends Frame implements ActionListener,WindowListener{
	TextField tf1 = new TextField();
	TextField tf2 = new TextField();
	TextField tf3 = new TextField();
	TextField result = new TextField();
	Button bt1 = new Button("计算");
	Max(){
		super("求三个数的最大值");
		add(tf1,BorderLayout.WEST);
		add(tf2,BorderLayout.NORTH);
		add(tf3,BorderLayout.EAST);
		add(result,BorderLayout.CENTER);
		add(bt1,BorderLayout.SOUTH);
		this.setSize(400,300);
		this.setVisible(true);
		bt1.addActionListener(this);
		this.addWindowListener(this);
		
		
	}
	public void actionPerformed(ActionEvent e) {
		int a = Integer.parseInt(tf1.getText());
		int b = Integer.parseInt(tf2.getText());
		int c = Integer.parseInt(tf3.getText());
		int max;
		if (a> b){
			max = a;
		}else{
			max = b;
		}
		if(c>max){
			max = c;
		}
		result.setText(new Integer(max).toString());
		
		
	}
	public void windowActivated(WindowEvent e) {
		// TODO Auto-generated method stub
		
	}
	public void windowClosed(WindowEvent e) {
		// TODO Auto-generated method stub
		
	}
	public void windowClosing(WindowEvent e) {
		e.getWindow().setVisible(false);
		e.getWindow().dispose();
		System.exit(0);
		
	}
	public void windowDeactivated(WindowEvent e) {
		// TODO Auto-generated method stub
		
	}
	public void windowDeiconified(WindowEvent e) {
		// TODO Auto-generated method stub
		
	}
	public void windowIconified(WindowEvent e) {
		// TODO Auto-generated method stub
		
	}
	public void windowOpened(WindowEvent e) {
		// TODO Auto-generated method stub
		
	}
	
	
}

public class test {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		 new Max();
	}

}