functional programming in Java

Question

how can you emulate functional programming in java, specifically, doing things like map a function to a collection of items?

map(func, new String[]{"a","b","c"});

what's the least verbose & awkward way to do it?

Answer 1

All attempts of functional programming will have some part of verbose and/or awkward to it in Java, until Java 8.

The most direct way is to provide a Function interface (such as this one form Guava) and provide all kinds of methods that take and call it (such as Collections#transfrom() which does what I think your map() method should do).

The bad thing about is that you need to implement Function and often do so with an anonymous inner class, which has a terribly verbose syntax:

Collection<OutputType> result = Collections.transform(input, new Function<InputType,OutputType>() {
    public OutputType apply(InputType input) {
      return frobnicate(input);
    }
});

Lambda expressions (introduced in Java 8) make this considerably easier (and possibly faster). The equivalent code using lambdas looks like this:

Collection<OutputType> result = Collections.transform(input, SomeClass::frobnicate);

or the more verbose, but more flexible:

Collection<OutputType> result = Collections.transform(input, in -> frobnicate(in));

Answer 2

I have used lambdaj and functionaljava for this sort of things. And there are probably others...