<?php

 function generate_code($length = 6) {

    $min = pow(10 , ($length - 1));

    $max = pow(10, $length) - 1;

    return rand($min, $max);

 }

public static String createRandom(boolean numberFlag, int length){

  String retStr = "";

  String strTable = numberFlag ? "1234567890" : "1234567890abcdefghijkmnpqrstuvwxyz";

  int len = strTable.length();

  boolean bDone = true;

  do {

   retStr = "";

   int count = 0;

   for (int i = 0; i < length; i++) {

    double dblR = Math.random() * len;

    int intR = (int) Math.floor(dblR);

    char c = strTable.charAt(intR);

    if (('0' <= c) && (c <= '9')) {

     count++;

    }

    retStr += strTable.charAt(intR);

   }

   if (count >= 2) {

    bDone = false;

   }

  } while (bDone);  

  return retStr;

 }