Java小程序有错误，高手帮忙指点下，在线等，谢谢！

import java.awt.*;
import java.awt.event.*;
class A extends Frame implements ActionListener
{TextField text1,text2,text3;
Button jia,cha,ji,chu;
A(String s)
{super(s);
setLayout(new FlowLayout());
text1=new TextField();
text2=new TextField();
text3=new TextField();
text3.setEditable(false);
jia=new Button("加");
cha=new Button("减");
ji=new Button("乘");
chu=new Button("除");
jia.addActionListener(this);
cha.addActionListener(this);
ji.addActionListener(this);
chu.addActionListener(this);
add(text1);
add(text2);
add(text3);
add(jia);
add(cha);
add(ji);
add(chu);
setBounds(100,100,200,200);
setVisible(true);
validate();
}
public void actionPerformed(ActionEvent e)
{try{int i,j,n;
i=Integer.parseInt(text1.getText());
j=Integer.parseInt(text2.getText());
if(e.getSource()==jia)