Streams

One of the top utilities included in Java 8 are Streams. In this chapter we are going to use lambdas in combination with Streams in small code fragments, and create a test to verify them.

To better understand what Streams are, what to do, and what not to do with them, it is highly recommended to read Oracle's Stream pages. A good starting point is https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html.

To cut a long story short, Streams provide a bunch of facilities to deal with long computations that can be executed either in parallel or sequential order. Parallel programming is out of the scope of this book, so the next examples will be sequential only. Furthermore, in order to keep the chapter concise we are going to focus on:

• filter
• map
• flatMap
• reduce

filter

Let's start with the filter operation. Filters is a function with a self-explanatory name; it filters in/out elements in the stream depending on whether the value satisfies a condition, as shown in the following example...