Java 8 Streams

First of all, please note that "Streams are not collections". java.util.stream is introduced to process elements in sequence. Streams are wrappers for collections and arrays. They wrap an existing collection to support operations expressed with lambdas, so you specify what you want to do, not how to do it. Also don't get confused with InputStream, java.util.stream does not have any relationship with InputStream or OutputStreams. java.util.stream are part of functional programming.

This page gives an examples on Java 8 Streams and how to use different kinds of Stream operations. You will learn about the processing order and how the ordering of stream operations affect runtime performance.

Streams differ from collections in several ways:

• No storage. A stream is not a data structure that stores elements; instead, it conveys elements from a source such as a data structure, an array, a generator function, or an I/O channel, through a pipeline of computational operations.
• Functional in nature. An operation on a stream produces a result, but does not modify its source. For example, filtering a Stream obtained from a collection produces a new Stream without the filtered elements, rather than removing elements from the source collection.
• Laziness-seeking. Many stream operations, such as filtering, mapping, or duplicate removal, can be implemented lazily, exposing opportunities for optimization. For example, "find the first String with three consecutive vowels" need not examine all the input strings. Stream operations are divided into intermediate (Stream-producing) operations and terminal (value- or side-effect-producing) operations. Intermediate operations are always lazy.
• Possibly unbounded. While collections have a finite size, streams need not. Short-circuiting operations such as limit(n) or findFirst() can allow computations on infinite streams to complete in finite time.
• Consumable. The elements of a stream are only visited once during the life of a stream. Like an Iterator, a new stream must be generated to revisit the same elements of the source.

If you are not familiar with Java 8 Lambda expressions, functional interfaces, method references, please refer them before start learning Streams.

Java 8 Streams Examples

1. How Java 8 Streams work?
2. Java 8 Streams parallelism introduction.
3. Explain non-interference behavior of Java 8 Streams.
4. Create Java 8 Stream using Stream.of() method example.
5. Create Java 8 Stream using List example.
6. Create Java 8 Stream using Stream.generate() method.
7. Java 8 Stream.filter() example.
8. Java 8 Stream.map() example.
9. Java 8 Stream flatmap method example.
10. Java 8 Stream peek method example.
11. Java 8 Stream distinct method example.
12. Java 8 Stream sorted method example.
13. Java 8 Stream limit method example.
14. Java 8 Stream forEach method example.
15. Java 8 Stream toArray method example.
16. Java 8 Stream reduce method example.
17. Java 8 Stream collect method example.
18. Java 8 Stream concat method example.
19. Java 8 Stream anyMatch(), allMatch() and noneMatch() example.
20. Java 8 Stream findFirst(), findAny() example.
21. Primitive type Stream example.