How to generate unique ID that is integer in java ?
A:
Just generate ID and check whether it is already present or not in your list of generated IDs.
Mykola Golubyev
2010-02-01 18:19:12
+6
A:
int uniqueId = 0;
int getUniqueId()
{
return uniqueId++;
}
Add synchronized if you want it to be thread safe.
Mark Byers
2010-02-01 18:19:49
Might want to add an exception for when it the integers get too high and roll over. Also might want to start uniqueId at Integer.MinInt() (Method is called something like that).
sixtyfootersdude
2010-02-01 23:08:51
This will work only when the process runs forever without stopping. For restarted apps, it will start from 0 each time.
talonx
2010-02-11 06:41:53
That doesn't return an integer. Format is hexstring, like `20e8f3d6-3f8d-475b-8c19-9619a78bbdc8`.
BalusC
2010-02-01 18:21:21
@BalusC: This is merely the String output you're talking about. Internally a UUID is a 128-bit value and hence could be interpreted as an integer (albeit BigInteger).
Adamski
2010-02-01 18:30:47
+20
A:
How unique does it need to be?
If it's only unique within a process, then you can use an AtomicInteger and call incrementAndGet() each time you need a new value.
Simon Nickerson
2010-02-01 18:20:19
+1
A:
It's easy if you are somewhat constrained.
If you have one thread, you just use uniqueID++; Be sure to store the current uniqueID when you exit.
If you have multiple threads, a common synchronized generateUniqueID method works (Implemented the same as above).
The problem is when you have many CPUs--either in a cluster or some distributed setup like a peer-to-peer game.
In that case, you can generally combine two parts to form a single number. For instance, each process that generates a unique ID can have it's own 2-byte ID number assigned and then combine it with a uniqueID++. Something like:
return (myID << 16) & uniqueID++
It can be tricky distributing the "myID" portion, but there are some ways. You can just grab one out of a centralized database, request a unique ID from a centralized server, ...
If you had a Long instead of an Int, one of the common tricks is to take the device id (UUID) of ETH0, that's guaranteed to be unique to a server--then just add on a serial number.
Bill K
2010-02-01 18:55:55
A:
If you really meant integer rather than int:
Integer id = new Integer(42); // will not == any other Integer
If you want something visible outside a JVM to other processes or to the user, persistent, or a host of other considerations, then there are other approaches, but without context you are probably better off using using the built-in uniqueness of object identity within your system.
Pete Kirkham
2010-02-01 19:21:20
A:
Do you need it to be;
- unique between two JVMs running at the same time.
- unique even if the JVM is restarted.
- thread-safe.
- support null? if not, use int or long.
Peter Lawrey
2010-02-04 22:08:10