How to Generate Unique ID in Java Integer

Question

How to generate unique ID that is integer in java that not guess next number

User · Answer

Just generate ID and check whether it is already present or not in your list of generated IDs

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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

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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

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import java util UUID    public class IdGenerator       public static int generateUniqueId                   UUID idOne   UUID randomUUID            String str    idOne                  int uid str hashCode            String filterStr    uid          str filterStr replaceAll  -                return Integer parseInt str                 XXX  replace with java util UUID      public static void main String   args            for  int i   0  i  lt  5  i                  System out println generateUniqueId                   generateUniqueId                         Hope this helps you

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Unique at any time   int uniqueId    int   System currentTimeMillis    amp  0xfffffff

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int uniqueId   0   int getUniqueId         return uniqueId        Add synchronized if you want it to be thread safe

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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  lt  lt  16   amp  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

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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

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UUID class

[java] How to Generate Unique ID in Java (Integer)?

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