JAVA学到方法写了一个四则运算计算器，请教一下有什么需要改进的

package method;
/*
 * 四则运算计算器
 * */

import java.util.Scanner;

public class Demo07
{
    public static void main(String[] args)
    {
        Scanner scanner = new Scanner(System.in);
        int a = 0;
        int num1 = 0, num2 = 0;
        System.out.println(\"请选择运行方法\");
        System.out.println(\"1.加法\\t2.减法\\t3.乘法\\t4.除法\");
        if (scanner.hasNextInt())
        {
            a = scanner.nextInt();
        }
        switch (a)
        {
            case 1 ->
            {
                System.out.println(\"请输入两个操作数\");
                if (scanner.hasNextInt())
                {
                    num1 = scanner.nextInt();
                    num2 = scanner.nextInt();
                }
                System.out.println(add(num1, num2));
            }
            case 2 ->
            {
                System.out.println(\"请输入两个操作数\");
                if (scanner.hasNextInt())
                {
                    num1 = scanner.nextInt();
                    num2 = scanner.nextInt();
                }
                System.out.println(sub(num1, num2));
            }
            case 3 ->
            {
                System.out.println(\"请输入两个操作数\");
                if (scanner.hasNextInt())
                {
                    num1 = scanner.nextInt();
                    num2 = scanner.nextInt();
                }
                System.out.println(mpc(num1, num2));
            }
            case 4 ->
            {
                System.out.println(\"请输入两个操作数\");
                if (scanner.hasNextInt())
                {
                    num1 = scanner.nextInt();
                    num2 = scanner.nextInt();
                }
                System.out.println(div(num1, num2));
            }
            default -> System.out.println(\"输入非法\");
        }
        scanner.close();
    }

    //加法运算
    public static int add(int num1, int num2)
    {
        return num1 + num2;
    }

    //减法运算
    public static int sub(int num1, int num2)
    {
        return num1 - num2;
    }

    //乘法运算
    public static int mpc(int num1, int num2)
    {
        return num1 * num2;
    }

    //除法运算
    public static int div(int num1, int num2)
    {
        return num1 / num2;
    }
}

来源：https://www.cnblogs.com/dreamxun/p/16973703.html
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