How to generate an unique ID for an class instance in Scala?

Question

I have a class that needs to write to a file to interface with some legacy C++ application. Since it will be instantiated several times in a concurrent manner, it is a good idea to give the file an unique name.

I could use System.currentTimemili or hashcode, but there exists the possibility of collisions. Another solution is to put a var field inside a companion object.

As an example, the code below shows one such class with the last solution, but I am not sure it is the best way to do it (at least it seems thread-safe):

case class Test(id:Int, data: Seq[Double]) {
    //several methods writing files...
}

object Test {
  var counter = 0

  def new_Test(data: Seq[Double]) = {
    counter += 1
    new Test(counter, data)
  }
}

use uuids perhaps? I'm a little unclear on what you're trying to accomplish. — James Adam, Feb 05 '14 at 14:19

score 33 · Answer 1 · edited Dec 11 '18 at 03:57

33

Did you try this :

def uuid = java.util.UUID.randomUUID.toString

See UUID javadoc, and also How unique is UUID? for a discussion of uniqueness guarantee.

edited Dec 11 '18 at 03:57

Eric Pohl

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answered Feb 05 '14 at 14:23

Gregosaurus

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I've looked at that, but it seems to be not guaranteed to be unique. – Feb 05 '14 at 18:40

score 8 · Accepted Answer · edited May 23 '17 at 12:08

8

it is a good idea to give the file an unique name

Since all you want is a file, not id, the best solution is to create a file with unique name, not a class with unique id.

You could use File.createTempFile:

val uniqFile = File.createTempFile("myFile", ".txt", "/home/user/my_dir")

Vladimir Matveev mentioned that there is a better solution in Java 7 and later - Paths.createTempFile:

val uniqPath = Paths.createTempFile(Paths.get("/home/user/my_dir"), "myFile", ".txt"),

edited May 23 '17 at 12:08

Community

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answered Feb 05 '14 at 14:23

senia

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Or, even better, [`Paths.createTempFile(Paths.get("/home/user/my_dir"), "myFile", ".txt")`](http://docs.oracle.com/javase/7/docs/api/java/nio/file/Files.html#createTempFile(java.nio.file.Path,%20java.lang.String,%20java.lang.String,%20java.nio.file.attribute.FileAttribute...)), if you're using Java 7 and later. – Vladimir Matveev Feb 05 '14 at 17:29
Why you write here `Paths.createTempFile`, shouldn't it be `Files.createTempFile` ? – Dfr May 30 '14 at 15:41

How to generate an unique ID for an class instance in Scala?

2 Answers2