随机验证码

import java.util.Random;
public class RandomGenDemo{
public static void main(String []args){
System.out.println("验证码如下："+RandomGen.codeGen());
}
}

class RandomGen{
//生成4位不重复的验证码
public static String codeGen(){
char[] codeSequence={'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z','0','1','2','3','4','5','6','7','8','9'};
Random random=new Random();
StringBuilder sb=new StringBuilder();//动态字符串
int count=0;
while(true){
//随机产生一个下标，通过下标取出字符数组中对应的字符
char c= codeSequence[random.nextInt(codeSequence.length)];
//假设取出的字符在动态字符串中不存在，代表没有重复
if(sb.indexOf(c+"")==-1){
sb.append(c);//追加到动态字符串中
count++;
if(count==4){
break;
}
}
}
return sb.toString();
}
}