生成不重复的随机数

要求：此随机数中只允许出现0-9的数字，a-z和A-Z
View Code
 1 package com.study.pratice03;
 2 
 3 import java.security.SecureRandom;
 4 import java.util.HashSet;
 5 import java.util.Set;
 6 
 7 class RandomString
 8 {
 9     private static final String POSSIBLE_CHARS = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
10     
11     public String getRandomString(int length)
12     {
13         StringBuffer sbf=new StringBuffer();
14         SecureRandom random = new SecureRandom();
15         for (int i = 0; i < length; i++)
16         {
17             sbf.append(POSSIBLE_CHARS.charAt(random.nextInt(POSSIBLE_CHARS
18                     .length())));
19         }
20         return sbf.toString();
21     }
22 }
23 public class RandomStringTest
24 {
25     public static void main(String[] args)
26     {
27         // TODO Auto-generated method stub
28         System.out.println(new RandomString().getRandomString(10));
29         //测试
30         /*for (int i = 0; i < 2000000; i++)
31         {
32             String s = new RandomString().getRandomString(10);
33             Set<String> check = new HashSet<String>();
34             if (check.contains(s))
35             {
36                 throw new IllegalStateException("重复字符被发现: " + s);
37             }
38             else
39             {
40                 System.out.println("产生第"+(i+1)+"个字符:"+s);
41                 check.add(s);
42             }
43         }*/
44     }
45 
46 }