public void testsort3(){

List<String> list = new ArrayList<String>();

Random random = new Random();

String k = null;

for(int i = 0;i < 10;i++){

String base = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";        

   StringBuffer sb = new StringBuffer();

   do{

   for (int j = 0; j < random.nextInt(10); j++) {     

        int number = random.nextInt(base.length());     

           sb.append(base.charAt(number));

           k = sb.toString();

       }

      }while(list.contains(k));

       list.add(k);

       System.out.println("添加字符串："+k); 

  }

System.out.println("排序前：");

for (String string : list) {

System.out.println(string);

}

Collections.sort(list);

System.out.println("排序后：");

for (String string : list) {

System.out.println(string);

}

}