验证码

package lianxi;
import java.util.*;
public class Yanzhengma {

    public static void main(String[] args) {
    String str="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
    int ary[]=new int[4];
    for (int i = 0; i <4; i++)
    {        
        Random r=new Random();
        //一共62个元素，ary[i]取值为0-61，是各个元素的索引,ary[i]+1取值1-62，确保了62个数都可以随机到
        ary[i]=r.nextInt(61);
        System.out.print(str.substring(ary[i],ary[i]+1));
    }    
  
    }

}