不完善的计算器

package com.zkn.myComputer;

import java.util.Scanner;

public class Computer {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入第一个数：");
        double num1 = scanner.nextDouble();
//
        System.out.println("请输入第一个符号：");
        String Str = scanner.next();
//
        System.out.println("请输入第二个数：");
        double num2 = scanner.nextDouble();
        scanner.close();
        switch (Str){
            case "+":
                System.out.println("num1 + num2");
                add(num1,num2);
                break;
            case "-":
                System.out.println("num1 - num2");
                subtraction(num1,num2);
                break;
            case "*":
                System.out.println("num1 × num2");
                multiplication(num1,num2);
                break;
            case "/":
                System.out.println("num1 / num2");
                division(num1,num2);
                break;
            default:
                System.out.println("输入了一个错误的运算符");
        }
    }
    //定义一种加法
    public static void add(double a,double b){
        System.out.println(a+b);
    }
    //定义一种减法
    public static void subtraction(double a,double b){
        System.out.println(a-b);
    }
    //定义一种乘法
    public static void multiplication(double a,double b){
        System.out.println(a*b);
    }
    //定义一种除法
    public static void division(double a,double b){
        System.out.println(a/b);
    }
}