Is there a Java version of Clojure's or Scala's persistent immutable vector?

Question

That is, immutable but data sharing with effectively O(1) indexing.

See also http://stackoverflow.com/questions/8575723/whats-a-good-persistent-collections-framework-for-use-in-java — om-nom-nom, Apr 24 '13 at 08:36

om-nom-nom · Accepted Answer · 2014-05-08T22:19:07.573

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Karl Krukow extracted clojure data structures into standalone library, so you can use it without bringing whole clojure to your project. There is also pcollections which has TreePVector implementation (with logarithmic time lookups).

edited May 08 '14 at 22:19

answered Apr 14 '13 at 10:35

om-nom-nom

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mikera · Answer 2 · 2013-04-14T23:46:47.543

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I made a library of persistent data structures for Java a couple of years back that may fit the bill:

https://github.com/mikera/mikera/tree/master/src/main/java/mikera/persistent

They are somewhat like the Clojure data structures, but with more of a Java flavour:

Make full use of generics
Support all the Java collection interfaces you would expect
Include some handy specialised types (e.g. RepeatList for repeated occurences of the same value)

edited Apr 14 '13 at 23:46

answered Apr 14 '13 at 13:09

mikera

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I use them a lot (whenever I don't want to pull in the whole of Clojure...), and maintain the code as open source. I think a few other people are using them. Basically, they are in a robust and usable state. – mikera Apr 14 '13 at 23:46

leonardoborges · Answer 3 · 2013-04-14T10:40:12.473

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Remember that Clojure, in the end, is just Java. As such you can just put Clojure's jar in your classpath and use its classes.

For instance, Clojure vectors are instances of clojure.lang.PersistentVector, maps are instances of clojure.lang.PersistentArrayMap and lists, instances of clojure.lang.PersistentList.

I haven't tried this in anger myself but that's probably the line I'd take if I wanted to use persistent data structures in Java.

Something like this could get you started:

import clojure.lang.PersistentVector;
...
ArrayList list = ...
PersistentVector myVector = PersistentVector.create(list);
// from here on, using myVector takes advantages of its persistent nature.

Obviously these classes were built with Clojure's API in mind, and not ease of use from Java - but it's certainly possible.

edited Apr 14 '13 at 10:40

answered Apr 14 '13 at 10:30

leonardoborges

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Thanks, but that is a heavyweight solution, and as you say the ease of use from Java is compromised. – Duncan McGregor Apr 14 '13 at 12:25
I'm curious. What's your use case? – leonardoborges Apr 14 '13 at 12:38
Having spent a year in Scala, not having what is effectively the default Scala collection is a bit painful! Guava helps with some functional constructs, but it's immutable collections are poor compared to Vector. – Duncan McGregor Apr 14 '13 at 19:54

score 0 · Answer 4 · answered Oct 14 '15 at 09:45

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Here is a Scala -> Java port: https://github.com/andrewoma/dexx

answered Oct 14 '15 at 09:45

tkruse

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Is there a Java version of Clojure's or Scala's persistent immutable vector?

4 Answers4