Java8 method reference used as Function object to combine functions

Question

Is there a way in Java8 to use a method reference as a Function object to use its methods, something like:

Stream.of(\"ciao\", \"hola\", \"hello         


        

Answer 1

You may also use

Function.identity().andThen(String::length).andThen(n -> n * 2)

The problem is, String::length is not necessarily a Function; it can conform to many functional interfaces. It must be used in a context that provides target type, and the context could be - assignment, method invocation, casting.

If Function could provide a static method just for the sake of target typing, we could do

    Function.by(String::length).andThen(n->n*2)

static  Function by(Function f){ return f; }

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For example, I use this technique in a functional interface

static  AsyncIterator by(AsyncIterator asyncIterator)

Syntax sugar to create an AsyncIterator from a lambda expression or a method reference.

This method simply returns the argument asyncIterator, which seems a little odd. Explanation:

Since AsyncIterator is a functional interface, an instance can be created by a lambda expression or a method reference, in 3 contexts:

 // Assignment Context
 AsyncIterator asyncIter = source::read;
 asyncIter.forEach(...);

 // Casting Context
 ((AsyncIterator)source::read)
     .forEach(...);

 // Invocation Context
 AsyncIterator.by(source::read)
     .forEach(...);

The 3rd option looks better than the other two, and that's the purpose of this method.