实验程序如下：
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Example1 extends JFrame {
 private int add=1,sub=2,mul=3,div=4;
 private int op=0;
 boolean ifOp;
 private String output="0";
 private Button[] jba=new Button[]{
 new Button("7"),new Button("8"),new Button("9"),new Button("+"),
 new Button("4"),new Button("5"),new Button("6"),new Button("-"),
 new Button("1"),new Button("2"),new Button("3"),new Button("*"),
 new Button("0"),new Button("."),new Button("="),new Button("/")};
 private JPanel jpt=new JPanel();
 private JPanel jpb=new JPanel();
 private JTextField jtf=new JTextField("");
 private Example1(){
  jpt.setLayout(new BorderLayout());
  jpt.add(jtf);
  this.add(jpt,BorderLayout.NORTH);
  jpb.setLayout(new GridLayout(4,4));
  for(int i=0;i<jba.length;i++){
  jpb.add(jba[i]);
  if(i==3||i==7||i==11||i==15||i==14)
  jba[i].addActionListener(new setOperate_Act());
  else
  jba[i].addActionListener(new setLabel_Act());
  }
  this.add(jpb,BorderLayout.CENTER);
  this.setSize(200, 200); 
  this.setResizable(false);
  this.setVisible(true);
  this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 }
 private void operate(String x){double x1=Double.valueOf(x);
 double y=Double.valueOf(output);
 switch(op){
 case 0:output=x;break;
 case 1:output=String.valueOf(y+x1);break;
 case 2:output =String.valueOf(y-x1);break;
 case 3:output =String.valueOf(y*x1);break;
 case 4:
 if(x1!=0) output=String.valueOf(y/x1);
 else output="不能为0";
 break;
 }
 }
 public String add(String x){
 operate(x);
 op=add;
 return output;
 }
 public String subtract(String x){
  operate(x);
  op=sub;
 return output;
 }
 public String multiply(String x){
  operate(x);
  op=mul;
 return output;
 }
 public String divide(String x){
  operate(x);
  op=div;
 return output;
 }
 public String Equals(String x){
  operate(x);
  op=0;
 return output;
 }
 public void opClean(){
  op=0;
  output="0";
 }
 class setOperate_Act implements ActionListener{
  public void actionPerformed(ActionEvent e) {
  if(e.getSource()==jba[3]){
  jtf.setText(add(jtf.getText()));
  ifOp=true;
  }
  else if(e.getSource()==jba[7]){
  jtf.setText(subtract(jtf.getText()));
  ifOp=true;
  }
  else if(e.getSource()==jba[11]){
  jtf.setText(multiply(jtf.getText()));
  ifOp=true;
  }
  else if(e.getSource()==jba[15]){
  jtf.setText(divide(jtf.getText()));
  ifOp=true;
  }
  else if(e.getSource()==jba[14]){
  jtf.setText(Equals(jtf.getText()));
  ifOp=true;
  }
  }
  }
  class setLabel_Act implements ActionListener{
  public void actionPerformed(ActionEvent e) {
  Button tempb=(Button)e.getSource();
  if(ifOp){
  jtf.setText(tempb.getLabel());
  ifOp=false;
  }else {
  jtf.setText(jtf.getText()+tempb.getLabel());
  }
  }
  }
 
 public static void main(String[] args) {
  new Example1();
 }
}