Saturday, January 8, 2011

Alphanumeric Random Number

Sometime basic things becomes tricky :-) Was trying to find out ways to generate some alphanumeric random number whose size (i.e. number of digits/alphabets) will be fixed and I should be able to decide that size. So, I came up with following algo-

1. ASCII table sequentially lists digits and alphabets e.g. ASCII code of 0 to 9 are ranging from 48 to 57. So I can use this sequential ASCII coding and convert them to Java Characters. Benefit, of course I can get rid of any array of predefined characters in my code.

2. I want to add current time to this "randomness", so need to initialize the seed of Java Random object with current timestamp. So every time I execute this, I can make sure it will be something different than previous instance.

3. As I already explained, it will be alphanumeric based, so I'll exclude special characters and thus, total number of valid ASCII chars left for me is 62 ( 0-9, A-Z, a-z ).

Now, let's see how the Java code looks like. Please let me know how random is this or any better approach :-) Cheers....   

       * It will generate ID- 16 digit ID
       * ASCII Table
       * 0-9 - ASCII code 48-57
       * A-Z - ASCII code 65-90
       * a-z - ASCII code 97-122
       * Total: 62
       * @return
      private String generateRandomID(){

            final int ID_SIZE = 16;
            final int NUM_OF_CHARS = 62;
            StringBuffer id = new StringBuffer();
            long now = new Date().getTime();
            // Set the new Seed as current timestamp
            Random r = new Random(now);
            int index = 0;
            int x = 0;
            while(x < ID_SIZE){
                  index = r.nextInt(NUM_OF_CHARS);
                  System.out.println("Index="+ index);
                  if(index < 10){
                        id.append((char)(48 + index));
                  else if(10 <= index && index <36){
                        index = index - 10;
                        id.append((char)(65 + index));
                        index = index - 36;
                        id.append((char)(97 + index));
            return id.toString();


  1. Excellent, stupendous. Great work man... ! carry on.

  2. was looking for this info... have fun man

  3. Awsome buddy. I really appreciate u.

  4. This does not generate random chars. Try putting it in for loop and call this function (generateRandomID()) and you will see what I mean. Nice try, though!

  5. Yeah Date().getTime() only changes every millisecond, so if you run this in the same millisecond you'll get the same result. It's probably better to initialize your Random once, outside your function. Or else use Math.random(), which does that for you.

  6. amazing....thank u it help us alot...