简单加减乘除计算器

 package com.kuang.method;
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 import java.util.Scanner;
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 public class Demo07 {
     public static void main(String[] args) {
         Scanner scanner = new Scanner(System.in);
         System.out.println("请输入第一个数");
         double a = scanner.nextDouble();
         System.out.println("请输入运算符号");
         String operation = scanner.next();
         System.out.println("请输入第二个数");
         double b = scanner.nextDouble();
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         switch (operation) {
             case "+":
                 System.out.println(a + operation + b + "=" + add(a, b));
                 break;
             case "-":
                 System.out.println(a + operation + b + "=" + sub(a, b));
                 break;
             case "*":
                 System.out.println(a + operation + b + "=" + mul(a, b));
                 break;
             case "/":
                 System.out.println(a + operation + b + "=" + div(a, b));
                 break;
             default:
                 System.out.println("输入错误");
         }
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         scanner.close();
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     }
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     //加法
     public static double add(double a, double b) {
         return a + b;
     }
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     //减法
     public static double sub(double a, double b) {
         return a - b;
     }
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     //乘法
     public static double mul(double a, double b) {
         return a * b;
     }
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     //除法
     public static double div(double a, double b) {
         return a / b;
     }
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 }