CODEWITHSUNDEEP
javauuiduniqueidentifier
Mohamed Saligh
Mohamed Saligh

Reputation: 12339

generate UUID of long type

Please give me sample code to generate UUID of long type in java without using timestamp.

Thanks

Upvotes: 6

Views: 23699

Answers (3)

Stephen C
Stephen C

Reputation: 718718

A real UUID is 128 bits. A long is 64 bits.

This is not just pedantry. UUID stands for Universal Unique IDentifier.

The "universal uniqueness" of the established UUID schemes are based on:

  • encoding a MAC address and a timestamp,
  • encoding a hash of a DNS name and a timestamp, or
  • using a 122 bit random number ... which is large enough that the probability of a collision is very very small.

With 64 bits, there are simply not enough bits for "universal uniqueness". For instance, the birthday paradox means that if we had a number of computers generating random 64 bit numbers, the probability of a potentially detectable collision would be large enough to be of concern.

Now if you just want a UID (not a UUID), then any 64-bit sequence generator will do the job, provided that you take steps to guard against the sequence repeating. (If the sequence repeats, then the IDs are not unique in time; i.e. over time a given ID may denote different entities.)

Upvotes: 22

Peter Lawrey
Peter Lawrey

Reputation: 533472

If you just want a simple unique long you can use AtomicLong.incrementAndGet(). This doesn't use a timestamp but does reset to 0 every time you start it and is not unique across JVMs.

What is the requirement not to use timestamps all about? UUID uses a timestamp. (amoungst other things)

Upvotes: 2

Raghuram
Raghuram

Reputation: 52635

Have you looked at java.util.UUID?

Upvotes: 7

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