java的随机字符串!!!!!!

package collection1;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;

public class Randomsort {

/**
 * @param args
 */
static List<String>stringList=new ArrayList<String>();

public void test1(){
   Random random=new Random();
   for(int i=0;i<10;i++){
      test2(random.nextInt(10)+1);
   }

}
public void test2(int length){
    Random random=new Random();
    String sb="abcdefghijkrmnopqrstuvwxyzABCDEFGHIJKRMNOPQRSTUVWXYZ0123456789";
    StringBuilder randomString=new StringBuilder(); 
    for(int i=0;i<length;i++){
        randomString.append(sb.charAt(random.nextInt(62)));

    }
    stringList.add(randomString.toString());
}
public static void main(String[] args) {
    // TODO Auto-generated method stub

  Randomsort rs=new Randomsort();
  rs.test1();
  System.out.println("------排序前------");
  for(String string:stringList){
      System.out.println("添加了随机字符串"+string);
  }
  Collections.sort(stringList);
  System.out.println("------排序后------");
  for(String string:stringList){
      System.out.println("添加了随机字符串"+string);
  }
}

}