A `java.util.Stream` represents a sequence of elements on which one or more operations can be performed. Stream operations are either _intermediate_ or _terminal_. While terminal operations return a result of a certain type, intermediate operations return the stream itself so you can chain multiple method calls in a row. Streams are created on a source, e.g. a `java.util.Collection` like lists or sets (maps are not supported). Stream operations can either be executed sequentially or parallely.
> You should also check out [Stream.js](https://github.com/winterbe/streamjs), a JavaScript port of the Java 8 Streams API.
> Streams are extremely powerful, so I wrote a separate [Java 8 Streams Tutorial](http://winterbe.com/posts/2014/07/31/java8-stream-tutorial-examples/). You should also check out [Stream.js](https://github.com/winterbe/streamjs), a JavaScript port of the Java 8 Streams API.
Let's first look how sequential streams work. First we create a sample source in form of a list of strings:
