[求助]计算器加法实现

谁能帮我看下程序,为什么我设置的计算器的加法代码不能实现,编译的结果是值在原来的结果上一直往上加,应该改哪里好呢?还有是当我按第二个加数时不能覆盖掉第一个加数,我写了清空的那句话了,不知道为什么啊?先谢谢大家了!
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;public class J_jisuan extends JFrame{
private JTextField[]m_textField={
new JTextField("",22)};
private JButton[]m_button={new JButton("1"),new JButton("2"),
                           new JButton("3"),new JButton("4"),
                           new JButton("5"),new JButton("6"),
                           new JButton("7"),new JButton("8"),
                           new JButton("9"),new JButton("0"),
                           new JButton(".")
                          };
private JButton[]n_button={ new JButton("+"),new JButton("-"),
                           new JButton("*"),new JButton("/"),
                           new JButton("="),new JButton("C")
                         };
Panel p1=new Panel();Panel p2=new Panel();
int i;
int f=0;
double x,y=0;


public J_jisuan(){
super("Calculator");
Container container=getContentPane();
container.setLayout(new BorderLayout());
container.add(p1,BorderLayout.NORTH);
container.add(p2,BorderLayout.CENTER);

p1.setLayout(new FlowLayout(FlowLayout.LEFT));
   
    p2.setLayout(new GridLayout(6,3));
   

    
p1.add(m_textField[0]);
for(int i=0;i<11;i++)
    p2.add(m_button[i]);
    for(int i=0;i<6;i++)
    p2.add(n_button[i]);
    
     
J_Handler handler =new J_Handler();
m_textField[0].addActionListener(handler);
for(int i=0;i<11;i++)
     m_button[i].addActionListener(handler);
     for(int i=0;i<6;i++)
     n_button[i].addActionListener(handler);


setSize(260,200);
setVisible(true);

}

private class J_Handler implements ActionListener{
public void actionPerformed(ActionEvent event){
String s="";
s=s+event.getActionCommand();
   for(int i=0;i<11;i++){
if(event.getSource()==m_button[i])

m_textField[0].setText(m_textField[0].getText()+event.getActionCommand());
}
if(event.getSource()==n_button[5]){//清除处理
m_textField[0].setText("");
x=0;f=0;s="";

}
if(event.getSource()==n_button[0]){//加号处理
x=Double.parseDouble(m_textField[0].getText());
m_textField[0].setText("");
m_textField[0].setText(""+(y+x));
y=y+x;f=1;
   }


if(event.getSource()==n_button[4]){//等号处理
x=Double.parseDouble(m_textField[0].getText());
if(f==1) m_textField[0].setText(""+(y+x));
y=0;
m_textField[0].setText(s+m_textField[0].getText());
}
  
  }


}

public static void main(String []args){
J_jisuan application=new J_jisuan();

application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
}