Functional Java is an open source library that seeks to improve the experience of using the Java programming language in a production environment. The library implements several advanced programming concepts that assist in achieving composition-oriented development. The JAR file will work with your Java 1.5 project without any additional effort. Functional Java is currently written using vanilla Java 1.5 syntax and requires no external supporting libraries. Lambdas introduced in Java 8 may be used in future development, these will be backported using the Retro Lambda project to be compatible with pre Java 8 bytecode.

Functional Java also serves as a platform for learning functional programming concepts by introducing these concepts using a familiar language. The library is intended for use in production applications and is thoroughly tested using the technique of automated specification-based testing with ScalaCheck.

Functional Java includes the following features:

Functional Java includes usage examples, here is one such example (import statements omitted) that maps a transformation across an array by adding 42 to each element.

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