Java persistent data structures

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Persistent data structures — immutable copy-on-write lists, maps and sets for Java

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grillbaer/persistentds

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README.md

Persistent Data Structures

Immutable copy-on-write collections for lists, maps and sets in Java. Based on auto-balancing binary trees.

Persistent collections simplify synchronization on shared data in multi-threaded applications because they guarantee immutability of already existing instances. They also make it easy to pass both old and new states to observers.

What does ‘persistent’ mean here?

A persistent collection is always immutable. Modification methods return new instances of the collection without changing the existing instance. So you don’t have to fiddle with error-prone and concurrency-restricting locking, because immutable data objects are thread-safe by nature. For good performance, peristentsds shares common parts between modified and previous versions of the data structures. This keeps the copy overhead as low as possible.

Syntax and behaviour of the persistent collections’ interfaces are similar to java.util.Collection . However, all modification methods return modified versions of the collection and will not change the original one.

Simply start with the static factory PersistentCollections to create new instances of persistent data structures.

Requires at least Java 8. Needs no other libraries.

For dependency declaration in various build systems or download of compiled jar see Maven Central.

You may use this Maven dependency with the latest version number:

dependency> groupId>io.github.grillbaergroupId> artifactId>persistentdsartifactId> version>x.x.xversion> dependency>

PersistentListInteger> list = PersistentCollections.persistentBinTreeList(); list = list.add(1).add(2).add(3); PersistentListInteger> modifiedList = list.add(4); System.out.println("Original list pl-s1">list + " => modified list pl-s1">modifiedList);

Original list= => modified list=

PersistentSetString> set = PersistentCollections.persistentBinTreeSet(); // or PersistentCollections.persistentHashSet(); set = set.put("A").put("B").put("C"); PersistentSetString> modifiedSet = set.remove("B"); System.out.println("Original set pl-s1">set + " => modified set pl-s1">modifiedSet);

Original set= => modified set=

PersistentMapInteger, String> map = PersistentCollections.persistentBinTreeMap(); map = map.put(1, "one").put(2, "two"); PersistentMapInteger, String> modifiedMap = map.put(3, "three"); System.out.println("Original map pl-s1">map + " => modified map pl-s1">modifiedMap);

Original map= <[1 ->one],[2 -> two]> => modified map= <[1 ->one],[2 -> two],[3 -> three]> 

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Persistent data structures — immutable copy-on-write lists, maps and sets for Java

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persistent-data-structure

Here are 21 public repositories matching this topic.

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PersistentObjectStorage is a simple libary for writing and reading persistent objects that are located in a set folder in the current user folder. The library is also capable of finding out if a program starts for the first time.

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JesseRussell411 / FunctionalJava

Persistent data structures and more. A collection of functional tools I’ve written for writing functional java.

jbgi / functionaljava

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cogumbreiro / part

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A collection of persistent data structures implemented in Java

aradzie/persistent

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README.md

A collection of persistent data structures written in Java

Any fool can write the Finger Tree data structure in Haskell, a purely functional language with expressive type system and lazy evaluation. But can you do this in Java, a vastly more verbose language with a weaker and clumsier type system? This repository contains the Enterprise Edition of Finger Tree, a pointless and stupid exercise, but very educational too. Because why not?

There are a few other persistent data structures too, such as:

• ArrayTrieHashMap
• PatriciaTrieHashMap
• Leaf-Leaning Red-Black Tree
• Queue, Stack, etc.

Probably none of this should be used in production, but might be used for the educational purposes.

The inspiring list of publications:

• Purely Functional Data Structures by Chris Okasaki
• Ideal Hash Trees by Phil Bagwell
• Finger trees: a simple general-purpose data structure by Ralf Hinze and Ross Paterson
• Left-LeaningRed-Black Trees by Robert Sedgewick

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A collection of persistent data structures implemented in Java

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