Introduction

Java 8 introduced the new Stream API. With streams, Java programmers can now use a more declarative style of writing programs that you have previously only seen in functional programming languages or functional programming libraries.

Using streams, you can now write more expressive programs with fewer lines of code, and easily chain multiple operations on large lists. Streams also make it simple to parallelize your operations on lists—that is, should you have very large lists or complex operations. One thing that is important to remember about streams is that, while it might appear as though they're an improved collection, they're actually not. Streams do not have any storage of their own; instead, they use the storage of the supplied source.

In Java, there are four types of streams: Stream, which is used for streaming objects; IntStream, which is for streaming integers; LongStream, which streams longs; and finally, DoubleStream, which, of course...