一个小型计算器程序，还有最后一个难点。。求指教
这个程序运行起来有3个TextField 想变成1个。就像电脑里的那个计算器一样，一个输入框，大哥大姐帮帮忙

import java.applet.*;
import java.awt.*;
import java.awt.event.*;

import javax.swing.JButton;
public class UseArithmetic extends Applet {



Label prompt,result;
TextField input1,input2,input3;
Button btn0,btn1, btn2, btn3, btn4, btn5, btn6, btn7, btn8, btn9, btn10, btn11, btn12, btn13,btn14,btn15;
double a=2, b=1,d=3;
String c="";
public void init( )
{
result=new Label("");
prompt = new Label("输入");
input1 = new TextField(5);
input2 = new TextField(5);
input3 = new TextField(5);  
btn0= new Button("0");
btn1= new Button("1");
btn2= new Button("2");
btn3= new Button("3");
btn4= new Button("4");
btn5= new Button("5");
btn6= new Button("6");
btn7= new Button("7");
btn8= new Button("8");
btn9= new Button("9");
btn10= new Button("+");
btn11= new Button("-");
btn12= new Button("*");
btn13= new Button("/");
btn14=new Button("=");
btn15=new Button(".");
add(result);
add(prompt);
add(input1);
add(input2);
add(input3);
add(btn0);
add(btn1);
add(btn2);
add(btn3);
add(btn4);
add(btn5);
add(btn6);
add(btn7);
add(btn8);
add(btn9);
add(btn10);
add(btn11);
add(btn12);
add(btn13);
add(btn14);
add(btn15);
btn0.addActionListener(new BtnActionAdapter());
btn1.addActionListener(new BtnActionAdapter());
btn2.addActionListener(new BtnActionAdapter());
btn3.addActionListener(new BtnActionAdapter());
btn4.addActionListener(new BtnActionAdapter());
btn5.addActionListener(new BtnActionAdapter());
btn6.addActionListener(new BtnActionAdapter());
btn7.addActionListener(new BtnActionAdapter());
btn8.addActionListener(new BtnActionAdapter());
btn9.addActionListener(new BtnActionAdapter());
btn10.addActionListener(new fuhaoActionAdapter());
btn11.addActionListener(new fuhaoActionAdapter());
btn12.addActionListener(new fuhaoActionAdapter());
btn13.addActionListener(new fuhaoActionAdapter());
btn14.addActionListener(new denghaoActionAdapter());
btn15.addActionListener(new BtnActionAdapter());
}
class BtnActionAdapter implements ActionListener{
public void actionPerformed(ActionEvent e)
{
if(input2.getText().equals("")){
   
//input1.setText(((Button) e.getSource()).getLabel());//getLel 为神马要加 是神马意思？？
input1.setText(input1.getText().concat(((Button)e.getSource()).getLabel().trim()));//不知道这公式为神马这么写 但知道他意思了trim是点号
  a =Double.parseDouble(input1.getText());
 
   
   
  } else {  
  input3.setText(input3.getText().concat(((Button)e.getSource()).getLabel().trim()));  
  b = Double.parseDouble(input3.getText());
  }

}
}
class fuhaoActionAdapter implements ActionListener{
public void actionPerformed(ActionEvent e)
{
input2.setText(((Button)e.getSource()).getLabel());
c=input2.getText();
}

 
}
class denghaoActionAdapter implements ActionListener{
public void actionPerformed(ActionEvent e)
{

double d=3;
if(("+".equals(c)) )
d=a+b;
else if(("-".equals(c)) )