练习代码输出不了东西，哪里错了

import java.util.ArrayList;

import java.util.Collections;

import java.util.List;

import java.util.Random;

public class CollectionsTest1 {

public void Testsort(){

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

String str="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqustuvwxyz0123456789";

StringBuilder C=new StringBuilder();

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

Random random=new Random();

int A=random.nextInt(10);

if(A==0){

continue;

}else{for(int B=0;B<A;B++){

int num=random.nextInt(str.length());

C.append(str.charAt(num));

}

}

while(stringList.contains(C.toString())){

stringList.add(C.toString());

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

for(String string:stringList){

System.out.println("元素："+string);

}

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

Collections.sort(stringList);

for (String string : stringList) {

System.out.println("元素："+string);

}

}

}

}

public static void main(String[] args) {

// TODO 自动生成的方法存根

CollectionsTest1 ct=new CollectionsTest1();

ct.Testsort(); 

}

}