多个不同随机字符串的生成

import java.util.*;
public class Test {
    public static void main(String[] args) {
        Test test = new Test();
        List<String> string = test.randomString(12, 10);//随机字符串的长度(12)和个数(10)
        System.out.println("----------排序前-----------");
        System.out.println("生成的10个随机字符串为：");
        for (String str : string) {
            System.out.println(str);
        }
        Collections.sort(string);
        System.out.println("----------排序后-----------");
        for (String str : string) {
            System.out.println(str);
        }
    }
        /*
         *length：生成的随机字符串的长度，times：生成的随机字符串的个数 
         */
    public List<String> randomString(int length,int times){
        List<String> string = new ArrayList<String>();
        String str =  "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        Random random = new Random();
        StringBuffer strBuf = new StringBuffer();
        for (int i = 0; i < times; i++) {
            for (int j = 0; j < length; j++) {
                int number = random.nextInt(62);
                strBuf.append(str.charAt(number));//重新给strBuf定义，防止它一直在后面append
            }
            if(!string.contains(strBuf)){
                string.add(strBuf.toString());
                strBuf = new StringBuffer();
            }else{
                i--;
            }
        }
        return string;
    }   
}