Java生成含字母和数字的6位随机字符串

package com.amos.tools;
 
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
 
public class InvertCodeGenerator {
 
  public static void main(String[] args) {
    // TODO Auto-generated method stub
    List<String> results=genCodes(6,100);
    System.out.println(results.size());
  }
 
  public static List<String> genCodes(int length,long num){
     
    List<String> results=new ArrayList<String>();
     
    for(int j=0;j<num;j++){
      String val = "";   
           
      Random random = new Random();   
      for(int i = 0; i < length; i++)   
      {   
        String charOrNum = random.nextInt(2) % 2 == 0 ? "char" : "num"; // 输出字母还是数字   
             
        if("char".equalsIgnoreCase(charOrNum)) // 字符串   
        {   
          int choice = random.nextInt(2) % 2 == 0 ? 65 : 97; //取得大写字母还是小写字母   
          val += (char) (choice + random.nextInt(26));   
        }   
        else if("num".equalsIgnoreCase(charOrNum)) // 数字   
        {   
          val += String.valueOf(random.nextInt(10));   
        }   
      }
      val=val.toLowerCase();
      if(results.contains(val)){
        continue;
      }else{
        results.add(val);
      }
    }
    return results;
           
        
    }  
   
 
}