import javax.swing.*;
public class Qiuhe  extends JFrame{
    JFrame a =new JFrame("求和工具");
    JPanel panel=new JPanel();
    JTextField field1=new JTextField(8);
     JButton button1=new JButton("+");
     JTextField field2=new JTextField(8);
     JButton button2=new JButton("=");
     JTextField field3=new JTextField(8);
     public Qiuhe()
     {
         panel.add(field1);
         panel.add(button1);
         panel.add(field2);
         panel.add(button2);
         panel.add(field3);
         a.add(panel);
          button2.addActionListener(new java.awt.event.ActionListener()
          { public void actionPerformed(java.awt.event.ActionEvent evt)
           {
            int x=Integer.parseInt(field1.getText())+Integer.parseInt(field2.getText());
            field3.setText(Integer.toString(x));
           }
          });
     }
public static void main(String[] args)
{
   
Qiuhe b=new Qiuhe();
b.setTitle("求和工具");
b.pack();
b.setDefaultCloseOperation(EXIT_ON_CLOSE);
b.setSize(400,100);
b.setVisible(true);
}
}程序没有错，但是为什么运行是结果出现的文本框不是计算器那样的呢？

太感谢两位了