A stream is a sequence of data that allows you to apply a sequence of operations (usually represented with lambda expressions) to it in a sequential or parallel way in order to filter, transform, sort, reduce, or construct a new data structure. It was introduced in Java 8 and was one of the most important features introduced in that version.

Streams are based on the Stream interface and some related classes and interfaces included in the java.util.stream package. They have also provoked the introduction of new methods in a lot of classes to generate streams from different data structures. You can create a Stream interface from every data structure that implements the Collection interface: from File, Directory, Array, and a lot of other sources.

Java also included different mechanisms to create streams from your own sources. The most important ones are:

• The Supplier interface: This interface defines the get() method. It will be called by Stream when it needs to process another object. You can create Stream from a Supplier interface using the generate() static method of the Stream class. Take into account that this source is potentially infinite, so you must use a method such as limit() or similar to limit the number of elements in Stream.
• The Stream.Builder interface: This interface provides the accept() and add() elements to add elements to Stream and the build() method, which returns the Stream interface created with the elements added before.
• The Spliterator interface: This interface defines the necessary methods to traverse and split the elements of a source. You can use the stream() method of the StreamSupport class to generate the Stream interface to process the elements of Spliterator.

In this chapter, you will learn how to implement your own Spliterator interface and how to create a Stream interface to process its data. We will work with a matrix of elements. A normal Stream interface should process one element at a time, but we will use the Spliterator class to implement one row at a time.