java随机

package com.lu;

import java.util.Random;
import java.util.Scanner;

public class Text2 {
    public static void main(String[] args) {
        //开发验证码
        Scanner input = new Scanner(System.in);
        System.out.println("请输入指定位数的：");
        randomNumbers(input.nextInt());


    }
    public static String randomNumbers(int n){//生成随机数
        Random r = new Random();
        String b ="";
        for (int i = 1; i <= n; i++) {
            int a = r.nextInt(3);
            switch (a){
                case 0 :
                    b += r.nextInt(10);//数字
                    break;
                case 1 :
                    b += (char)r.nextInt(65,91);//大写字母
                    break;
                case 2 :
                    b += (char)r.nextInt(97,123);//小写字母
                    break;
            }
        }
        System.out.println(b);
        return b;
    }


}