RandomUtils给一个随机数的个数,返回随机数

package com.utils;

import java.util.Random;

public class RandomUtils {
// public static StringBuffer sb =new StringBuffer();

public static String getRandom(int num){
    String sb =new String();
    int index;
    char[] ch = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".toCharArray();
    Random r =new Random();
    int length =ch.length;
    for(int i=0;i

}