On Java 8 as a hybrid-style language

[Joel Neely]

Java seems always to have allowed a mostly-Object-Oriented style, but not really forced it. (Auto-[un]boxing has helped, but the wallpaper over that seam isn't completely smooth.) This introduced procedurally-minded programmers to OO more gradually (benefit), but also allowed them to believe they were doing OO without fully embracing the OO programming style (dubious).

So the lessons of OO from other languages have taken quite a while to percolate through the Java community.

It would appear that Java 8 is (belatedly) beginning to bolt on specific features from Functional Programming in much the same way, allowing but not fully embracing FP style.

What sources/resources do you recommend to help legacy Java programmers really understand FP, rather than simply regarding lambdas, streams, etc. as added language features stirred into a procedural+OO+FP gumbo?

[Cay Horstmann]

In my unfashionable opinion, if you want to learn functional programming at a deep level, you want to learn it with a functional programming language. You could learn Scheme with http://mitpress.mit.edu/sicp/, or Haskell with http://learnyouahaskell.com/. After many months of useful preparation, you'll pick up the Java 8 lambdas in a few minutes :-)

For the language enthusiast, that route is highly recommended. But anyone can pick up Java 8 lambdas in a short amount of time and just use them, without having to know fixed point theorems or category theory.

Cheers,

Cay