java switch语句里case穿透

import java.util.Scanner;
public class demo {
	public static void main(String[] args) {
		Scanner season = new Scanner(System.in);
		System.out.println("请输入月份");
		int a = season.nextInt();
		
		switch(a) {
			case 3:
			case 4:
			case 5:
				System.out.println(a + "月是春季");
				break;
			case 6:
			case 7:
			case 8:
				System.out.println(a + "月是夏季");
				break;
			case 9:
			case 10:
			case 11:
				System.out.println(a + "月是秋季");
				break;
			case 12:
			case 1:
			case 2:
				System.out.println(a + "月是冬季");
				break;
			default:
				System.out.println("月份输入有误");
				break;
			
		}
	}
}

Java 里反转数组（和js里区别很大）

package test_demo;

public class demo {
    public static void main(String[] args) {
        int[] arr = {3, 6, 8, 44, 90, 32};
        int[] arr1 = {};
        for (int star = 0, end = arr.length - 1; star <= end; star++, end--) {
            int temp = arr[end];
            arr[end] = arr[star];
            arr[star] = temp;
        }
        System.out.print("[");
        for(int i = 0; i< arr.length;i++) {
            if (i == arr.length-1) {
                System.out.print(arr[i]);
            } else {
                System.out.print(arr[i] + ",");
            }
        }
        System.out.println("]");
    }
}

Java里用 方法 反转数组

package test_demo;

public class demo {
    public static void main(String[] args) {
        int[] arr = {3, 6, 8, 44, 90, 32, 66};
        getReveser(arr);
    }

    public static void getReveser(int[] arr) {
        for (int star = 0, end = arr.length - 1; star <= end; star++, end--) {
            int temp = arr[end];
            arr[end] = arr[star];
            arr[star] = temp;
        }
        System.out.print("[");
        for (int i = 0; i < arr.length; i++) {
            if(i == arr.length- 1) {
                System.out.print(arr[i]);

            } else  {
                System.out.print(arr[i] + ", ");
            }
        }
        System.out.println("]");
    }
}

统计字符次数

package test_demo;

import java.util.Scanner;

public class demo {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入一个字符串：");
        String s = sc.nextLine();
        int num1 = 0;
        int num2 = 0;
        int num3 = 0;
        String A = "";
        String a = "";
        String aa = "";
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) >= 'A' && s.charAt(i) <= 'Z') {
                A = A + s.charAt(i);
                num1 += 1;
            } else if (s.charAt(i) >= 'a' && s.charAt(i) <= 'z') {
                a = a + s.charAt(i);
                num2 += 1;
            } else if (s.charAt(i) >= '0' && s.charAt(i) <= '9') {
                aa = aa + s.charAt(i);
                num3 += 1;
            }
        }
        System.out.println(A);
        System.out.println("大写字母个数" + num1);
        System.out.println(a);
        System.out.println("小写字母个数" + num2);
        System.out.println(aa);
        System.out.println("数字个数" + num3);
    }
}

反转字符串

package test_demo;

import java.util.Scanner;

public class demo {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入一个字符串：");
        String s = sc.nextLine();
        String line = getStr(s);
        System.out.println(line);
    }

    public static String getStr(String s) {
        String line = "";
        for (int i = s.length()-1; i >= 0; i--) {
            line += s.charAt(i);
        }
        return line;
    }
}

用StringBuilder reverse方法反转字符串

package test_demo;

import java.util.Scanner;

public class demo {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入一个字符串");
        String s = sc.nextLine();

        String ss = reverse(s);
        System.out.println(ss);
    }

    public static String reverse(String s) {
//        StringBuilder sb = new StringBuilder(s);
//        sb.reverse();
//        String ss = sb.toString();
        return new StringBuilder(s).reverse().toString();
//        return ss;
    }
}