Random y=new Random(); int s=y.nextInt(37); String a="s7q8r5s2b1g2d3s6a9f5c1v2f5h6j8g9p6h9f8c1"; System.out.println(a.substring(s, s+4));
基本思路：首先插入一段数字与字母的字符串；
然后利用随机数生成随机数；
然后用生成的随机数作为索引，截取该数的后面四位。
输出结果：
第二种方法
基本思路
1、定义一个String[]zimu={"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"};
2、生成随机数作为索引
3、生成10以内的数字
4、输出。
String[]zimu={"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"};
Random suoyin=new Random();
Random shu=new Random();
System.out.println(zimu[suoyin.nextInt(27)]+shu.nextInt(10)+zimu[suoyin.nextInt(27)]+shu.nextInt(10));
输出结果
原文：http://www.cnblogs.com/mutougezi/p/5487394.html