java实现简单的加减乘除计算器

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.awt.FlowLayout;

import javax.swing.*;

@SuppressWarnings("unused")
class Sumjp {
 
 JOptionPane jp = new JOptionPane();
 Sumjp(String str) {
  JOptionPane.showMessageDialog(null, str);
  System.exit(0);
 }
 Sumjp(String[] str){
  
 }
}

public class JiSuan extends JFrame implements ActionListener,ItemListener{
 
 
 private static final long serialVersionUID = 1L;
 double x1,x2,sum = 0;
 String f;
 
 JTextField txt = new JTextField(30);
 JTextField txt1 = new JTextField(5);
 JTextField txt2 = new JTextField(5);
 JTextField txt3 = new JTextField(5);
 JLabel lb1 = new JLabel("数据1：");
 JLabel lb2 = new JLabel("符号：");
 JLabel lb3 = new JLabel("数据2：");
 JButton jbtn = new JButton("确定");
 
 JiSuan(){
  setSize(350,150);
  setVisible(true);
  setTitle("计算器:");
  setDefaultCloseOperation(EXIT_ON_CLOSE);
  setLayout(new FlowLayout());
  add(lb1);
  add(txt1);
//  add(lb2);
//  add(txt2);
  JComboBox<String> jc = new JComboBox<String>();
  jc.addItem("加");
  jc.addItem("减");
  jc.addItem("乘");
  jc.addItem("除");
  add(jc);
  add(lb3);
  add(txt3);
  add(jbtn);
  add(txt);
  validate();
  jc.addItemListener(this);
  jbtn.addActionListener(this);
 }
 public void itemStateChanged(ItemEvent ie){
  f = (String)ie.getItem().toString();
 }
 public void actionPerformed(ActionEvent e){
  x1 = Double.parseDouble(txt1.getText());
  //f = txt2.getText();
  x2 = Double.parseDouble(txt3.getText());
  if(f.equals("加")){
   sum = x1 + x2;
  }
  if(f.equals("减")){
   sum = x1 - x2;
  }
  if(f.equals("乘")){
   sum = x1*x2;
  }
  if(f.equals("")){
   sum = x1/x2;
  }
  txt.setText(x1 + f + x2 + "=" + sum);
  new Sumjp(x1 + f + x2 + "=" + sum);
 }
 public static void main(String[] args) {
  // TODO 自动生成的方法存根
  new JiSuan();
 }

}

public class Calculator
{
 public static void main(String[] args){
  java.util.Scanner s = new java.util.Scanner(System.in);
  System.out.println("欢迎使用简单计算器");

  System.out.print("请输入第一个数字：");
  int num1 = s.nextInt();

  System.out.print("请输入运算符：");
  String operator = s.next();

  System.out.print("请输入第二个数字：");
  int num2 = s.nextInt();

  int result = 0;

  switch (operator){
   case "+":
     result = num1 + num2;
     break;
   case "-":
     result = num1 - num2;
     break;
   case "*":
     result = num1 * num2;
     break;
   case "/":
     result = num1 * num2;
     break;
   case "%":
     result = num1 % num2;
  }
  
  System.out.println(num1+operator+num2+"="+result);
 }
}