generate a random string with a-z and 0-9 in java

/**
 * @author lautturi.com 
 * Java example: java create a random string with a-z and 0-9
 */

import java.util.*;

public class Lautturi {
	
	public static void main(String[] args) {
		String chars = "0123456789"
                + "abcdefghijklmnopqrstuvwxyz"
                ;
		int len = 15;
		
        StringBuilder sb = new StringBuilder(len);
        for (int i = 0; i < len; i++)
            sb.append(chars.charAt(new Random().nextInt(chars.length())));
        String randomString =  sb.toString();
		System.out.println("random string:"+ randomString);
	}
}

output:

random string:4h05giih6y1iy5w