Besides lambdas expressions, Java 8 introduced another language syntax change in the form of a new operator, :: (double colon), to create so-called method references. Even though I talked about and used method references in earlier articles, it’s time to take a closer look.
The three methods, map, filter, and reduce, are the cornerstone of any functional programming. Usually, our data pipelines consist of one or more intermediate operations, transforming (aka mapping) and/or filtering elements, and a terminal operation to gather the data again (aka reducing).
In my previous articles about functional programming, I’ve shown how to incorporate a more functional style into our Java code. But I’ve omitted a crucial topic: how to deal with exceptions.
As laid out in the first piece, immutability is one of the core concepts of functional programming. Real functional programming languages support it by design, at a language-level. But in Java and most non-functional languages, we need to design and implement it ourselves, at code-level.
Java 8 gave us the Stream API, a lazy-sequential data pipeline of functional blocks. It isn’t implemented as a data structure or by changing its elements directly. It’s just a dumb pipe providing the scaffolding to operate on, making it really a smart pipe.