Java利用Scanner类实现两个数的加，减，乘，除法。

import java.util.Scanner;

public class Demo1 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入计算方式（即输入加法，减法，乘法，除法其中一个）");
            switch (scanner.next()){
                case "加法":
                    System.out.println("请输入加数，并点击Enter键位确认");
                    double sum = scanner.nextDouble();
                    System.out.println("请输入被加数，并点击Enter键位确认");
                    double n = scanner.nextDouble();
                    sum = sum + n;
                    System.out.println("相加和为：" + sum);
                    break;

                case "减法":
                    System.out.println("请输入被减数，并点击Enter键位确认");
                    double sum1 = scanner.nextDouble();
                    System.out.println("请输入减数，并点击Enter键位确认");
                    double n1 = scanner.nextDouble();
                    sum1 = sum1 - n1;
                    System.out.println("相减差为：" + sum1);
                    break;

                case "乘法":
                    System.out.println("请输入乘数，并点击Enter键位确认");
                    double sum2 = scanner.nextDouble();
                    System.out.println("请输入被乘数，并点击Enter键位确认");
                    double n2 = scanner.nextDouble();
                    sum2 = sum2 * n2;
                    System.out.println("相减差为：" + sum2);
                    break;

                case "除法":
                    double num = 0;
                    System.out.println("请输入被除数，并点击Enter键位确认");
                    double sum3 = scanner.nextDouble();
                    System.out.println("请输入除数，并点击Enter键位确认");
                    double n3 = scanner.nextDouble();
                    sum3 = sum3 / n3;
                    System.out.println("商为：" + sum3);
                    break;

                default:
                    System.out.println("输入错误，请重新输入。");
            }
        scanner.close();
    }
}