java 产生随机字符串

产生随机字符串的一种简单有效的方法，见如下java代码

package com.bjhit.eranges.common.util;public class BjhitRandomStr {public static String generateRandomStr(int num) {if (num > 0) {char[] tmp = new char[num];for (int i = 0; i < num; i++) {tmp[i] = getRandomChar();}return String.valueOf(tmp);} else {return null;}}private static char getRandomChar() {char[] arr = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ".toCharArray();char c = arr[(int)(Math.random()*arr.length)];return c;}public static void main(String argv[]) {System.out.println(generateRandomStr(6));}}