public void testChallenge() {

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

String substring="0123456789qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM";

      Random random=new Random();

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

StringBuilder sb=new StringBuilder();

   do{

   int  ss=random.nextInt(10);

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

int sbint=random.nextInt(62);

sb.append(substring.charAt(sbint));

         }

    }while(newst.contains(sb));//保证字符串不重复

newst.add(sb.toString());

}

System.out.println("---------------排序前");

for(String st1:newst) {

System.out.println("排序前的字符串为："+st1);

}

System.out.println("----------排序后");

Collections.sort(newst );

for(String st1:newst) {

System.out.println("排序后的字符串为："+st1);

}

}