java-获取随机字符串

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);
}
}