Functional Programming in Java

Question

Is there a good library for functional programming in Java?

I'm looking for stuff like Predicate and List.Find() (as a static method). Not complicated to implement, but it would be nice to find reuse a library here.

Answer 1

Functional Java is one that's worth taking a look at and FunctionalJ is another.

Answer 2

FunctionalJava is the best known library; it makes use of Java closures (BGGA) for examples:

final Array<Integer> a = array(1, 2, 3);  
final Array<Integer> b = a.map({int i => i + 42});  
arrayShow(intShow).println(b); // {43,44,45}

EDIT

Check also lambdaj.

Further EDIT

BGGA is entirely optional. It just makes for nicer syntax.

Answer 3

Google collections has a decent selection of functional-programming style utility methods. Some classes of interest are Iterables, Iterators, Function, Functions, etc

It also has a bunch of collection classes as well!

Answer 4

scala is a functional programming language that is fully compatible with java (runs through the jvm). It offers a beautiful mix of object-oriented and functional techniques along with many improvements over java in generics and concurrency. Some even say it could replace java.

Answer 5

Jambda is another FP-library. From the documentation:

Jambda is an attempt to provide the Java(TM) world with tools and concepts from functional programming (FP).

The goals are several:

• To provide Java programmers with expressive FP constructs
• To provide a bridge for Java programmers into the FP-world
• To see how far Java and generics can be stretched

This document is an attempt to introduce Java programmers into the FP world, and at the same time explain some (or most) of the features in Jambda.

Answer 6

If you want a pure Java solution check out lambdaj

http://code.google.com/p/lambdaj/

Besides the possibility to define and use closure in a DSL-style, it also allows to manipulate collections in a functional way, without explicitly write closures or loops

Answer 7

I suggest bolts:

http://bitbucket.org/stepancheg/bolts/

Unlike similar libraries, JDK standard collections are wrapped, and functional operations (map, filter, reduce etc.) are methods of collection interfaces. It is convenient.