2023-03-06 java switch+case的用法，从好多选项中选出符合条件的选项，相比if的效率高一些，例题：1.输出某年某月有多少天 2.分数成绩是优秀，良好还是及格

本文链接：https://blog.youkuaiyun.com/m0_51258807/article/details/129361186

本文通过两个实例——输出某年某月的天数和判断分数等级（优秀、良好、及格），详细介绍了Java中switch+case语句的使用方法，对比if语句，展示了其在效率上的优势。

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1.

    @Test
     public void test10(){
        //输入月份，判断该月有多少天int
        System.out.println("请输入年份和月份：");
       Scanner scanner = new Scanner(System.in);
       int year = scanner.nextInt();
       int month = scanner.nextInt();
        if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)) {
            System.out.println(+year + "是闰年");
            if(month == 2){
                System.out.println("2月有29天");
            }
        } else {
            System.out.println(+year + "是平年");
            if(month == 2){
                System.out.println("2月有28天");
            }
        }

       switch (month) {
           case 1:
           case 3:
           case 5:
           case 7:
           case 8:
           case 10:
           case 12:
               System.out.println("有31天");
               break;

           case 4:
           case 6:
           case 9:
           case 11:
               System.out.println("有30天");
               break;
       }

    }

@Test
 public void test10(){
    //输入月份，判断该月有多少天int
    System.out.println("请输入年份和月份：");
   Scanner scanner = new Scanner(System.in);
   int year = scanner.nextInt();
   int month = scanner.nextInt();
    if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)) {
        System.out.println(+year + "是闰年");
        if(month == 2){
            System.out.println("2月有29天");
        }
    } else {
        System.out.println(+year + "是平年");
        if(month == 2){
            System.out.println("2月有28天");
        }
    }

switch (month) {
    case 1:
    case 3:
    case 5:
    case 7:
    case 8:
    case 10:
    case 12:
        System.out.println("有31天");
        break;

    case 4:
    case 6:
    case 9:
    case 11:
        System.out.println("有30天");
        break;
}  
     
}

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2.简洁版

    @Test
    public void test11(){
        //输入月份，判断该月有多少天int
        System.out.println("请输入月份：");
        Scanner scanner = new Scanner(System.in);
        int month = scanner.nextInt();
        while( month > 12 || month < 1 ){
            System.out.println("输入不合法，请重新输入：");
            month = scanner.nextInt();
        }

        switch (month) {
            case 1:
            case 3:
            case 5:
            case 7:
            case 8:
            case 10:
            case 12:
                System.out.println("有31天");
                break;

            case 4:
            case 6:
            case 9:
            case 11:
                System.out.println("有30天");
                break;

            case 2:
                System.out.println("请输入年份：");
                int year = scanner.nextInt();
                if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)) {
                    System.out.println(+year + "是闰年,2月有29天");
                } else {
                    System.out.println(+year + "是平年,2月有28天");
                }
        }
    }

@Test
public void test11(){
    //输入月份，判断该月有多少天int
    System.out.println("请输入月份：");
    Scanner scanner = new Scanner(System.in);
    int month = scanner.nextInt();
    while( month > 12 || month < 1 ){
    System.out.println("输入不合法，请重新输入：");
    month = scanner.nextInt();
}

    switch (month) {
        case 1:
        case 3:
        case 5:
        case 7:
        case 8:
        case 10:
        case 12:
            System.out.println("有31天");
            break;

        case 4:
        case 6:
        case 9:
        case 11:
            System.out.println("有30天");
            break;

        case 2:
            System.out.println("请输入年份：");
            int year = scanner.nextInt();
            if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)) {
                System.out.println(+year + "是闰年,2月有29天");
            } else {
                System.out.println(+year + "是平年,2月有28天");
            }
    }
}

3.分数成绩是优秀，良好还是及格

 @Test
    public void test12(){
        System.out.println("请输入成绩：");
        Scanner scanner = new Scanner(System.in);
        int score = scanner.nextInt();
        switch(score /  10){
            case 10:
                System.out.println("大神！");
                break;
            case 9:
                System.out.println("优秀！");
                break;
            case 8:
                System.out.println("良好！");
                break;
            case 7:
                System.out.println("可以！");
                break;
            case 6:
                System.out.println("勉强及格！");
                break;
            default:
                System.out.println("需要努力啊！");
                break;
        }
    }

@Test
public void test12(){
    System.out.println("请输入成绩：");
    Scanner scanner = new Scanner(System.in);
    int score = scanner.nextInt();
    switch(score /  10){
        case 10:
            System.out.println("大神！");
            break;
        case 9:
            System.out.println("优秀！");
            break;
        case 8:
            System.out.println("良好！");
            break;
        case 7:
            System.out.println("可以！");
            break;
        case 6:
            System.out.println("勉强及格！");
            break;
        default:
            System.out.println("需要努力啊！");
            break;
    }
}