import java.util.Random; public class getRandomString { public static String excute(int length) { StringBuffer buffer = new StringBuffer("0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"); StringBuffer sb = new StringBuffer(); Random r = new Random(); int range = buffer.length(); for (int i = 0; i < length; i ++) { sb.append(buffer.charAt(r.nextInt(range))); } return sb.toString(); } public static void main(String args[]) { String res = excute(4); System.out.println(res); } }