Unique number generation in JdK1.4

[Shashidhar Yarabati]

Hello All

My guys here managed to get the unique number wiht Math.random(). Till now (around 3 years) it is working fine, now we got an issue which shows two sessions (not sessionId, we are using this unique number for other reasons) are running with same unique number.

The problem here is, I can't use UUID class because my application is running under Jdk1.4.

Can any help me to impelement the best solution here...!!

THanks in Advance

[Carey Evans]

The Java 5 UUID is essentially a 122-bit random number, compared to Math.random() which is a 53-bit random number, so collisions are only much less likely with a UUID, not impossible.

That said, you could generate a 128-bit random number like this:

Random rand = new Random();
byte[] b = new byte[16];
rand.nextBytes(b);

If you want to avoid collisions altogether, you'll have to test for them before returning the number.

[Shashidhar Yarabati]

Will this really guarantee me to get unique number?

One thing I can't do is I can't keep track of generated numbers to check.

Please help me to think..........! I am running out of time

[Manuel Leiria]

Originally posted by Shashidhar Yarabati:
Will this really guarantee me to get unique number?

One thing I can't do is I can't keep track of generated numbers to check.

Please help me to think..........! I am running out of time

There's no way this will guarantee the uniqueness because...it's a random number!
I can't see any other way but keeping track of the generated numbers.

[Shashidhar Yarabati]

Does any one now how to add synchronize keyword to Math.random?

My code is:

Integer globalTicketID = null;
do {
globalTicketID = new Integer(Math.round((float) Math.random() * 10000000));
} while (mGlobalTkt.containsKey(globalTicketID));

I hear that we can fix by adding a single synchronize keyword.

I didn't see that in API

Can any one know how to do this?

[Jesper de Jong]

You cannot make Math.random() return unique numbers by using the synchronized keyword. Where did you hear this?

[Rob Spoor]

Inside your JDK (5.0 or 6) folder there is a file called src.zip. Inside it you can find the source code of java.util.UUID. You can use it as a hint on how to implement something similar.

I'm saying something similar, and not copy the file, because of the copyrights this file has.

[Steve Fahlbusch]

Now does the number have to be 'unique' and 'random' or just 'unique'?