JAVA --控制流程(二)

亦凉 2022-11-27 12:26 167阅读 0赞

## switch语句 ##

public class BMI{
        
    	public static void main(String args[]) {
        
    		int day = 5;
    		switch(day) {
        
    		case 1:
    			System.out.println("今天星期一");
    			break;
    		case 2:
    			System.out.println("今天星期二");
    			break;
    		case 5:
    			System.out.println("今天星期五");
    			break;
    		default:
    			System.out.println("这是什鬼？");
    		}
    	}
    }

> 注意这里的break每个语句后都需要加

**综合练习**，**判断月份**

import java.util.Scanner;
    public class BMI{
        
    	public static void main(String args[]) {
        
    		System.out.println("请输入月份:");
    		Scanner s = new Scanner(System.in);
    		int month = s.nextInt();
    		switch(month) {
        
    		case 3:
    		case 4:
    		case 5:
    			System.out.println("现在是春季");
    		break;
    		case 6:
    		case 7:
    		case 8:
    			System.out.println("现在是夏季");
    		break;
    		case 9:
    		case 10:
    		case 11:
    			System.out.println("现在是秋季");
    		break;
    		case 12:
    		case 1:
    		case 2:
    			System.out.println("现在是冬季");
    		default:
    			System.out.println("这是什么鬼?");
    		}
    	}
    }

另一种写法（dealut没有给m赋值所以要先赋值）

import java.util.Scanner;
    public class BMI{
        
    	public static void main(String args[]) {
        
    		String m = "5"; //初始化赋值
    		System.out.println("请输入月份:");
    		Scanner s = new Scanner(System.in);
    		int month = s.nextInt();
    		switch (month) {
        
    		case 3:
    		case 4:
    		case 5:
    			m = "春天";
    			break;
    		case 6:
    		case 7:
    		case 8:
    			m = "夏天";
    			break;
    		case 9:
    		case 10:
    		case 11:
    			m = "秋天";
    			break;
    		case 12:
    		case 13:
    		case 14:
    			m = "冬天";
    			break;
    		default:
    			System.out.println("什么鬼?");
    		}
    		System.out.println(m);
    	}
    }

> 注意！！！m必须初始化赋值，否则造成空指针现象！

正确写法

import java.util.Scanner;
    public class BMI{
        
    	public static void main(String args[]) {
        
    		System.out.println("请输入月份:");
    		Scanner s = new Scanner(System.in);
    		int month = s.nextInt();
    		String season;
    		switch (month) {
        
    		case 3:
    		case 4:
    		case 5:
    			season = "春天";
    			break;
    		case 6:
    		case 7:
    		case 8:
    			season = "夏天";
    			break;
    		case 9:
    		case 10:
    		case 11:
    			season = "秋天";
    			break;
    		case 12:
    		case 13:
    		case 14:
    			season = "冬天";
    			break;
    		default:
    			season = "什么鬼";
    		}
    		System.out.println(season);
    	}
    }