Java Stream Basics

What is a Stream?

A Stream in Java is a sequence of elements supporting sequential and parallel aggregate operations.

Streams do not store data; instead, they convey elements from a data source such as collections, arrays, or I/O channels.

Streams allow functional-style operations on data, such as map, filter, and reduce.

• Streams are not data structures.
• They provide a pipeline to process data.
• Operations on streams are either intermediate or terminal.

Creating Streams

Streams can be created from various data sources including collections, arrays, or generated values.

Common ways to create streams include using the stream() method on collections or Stream.of() for explicit elements.

• From a Collection: collection.stream()
• From an Array: Arrays.stream(array)
• From explicit values: Stream.of(value1, value2, ...)
• From infinite generators: Stream.generate() or Stream.iterate()

Stream Operations

Stream operations are divided into intermediate and terminal operations.

Intermediate operations return a new stream and are lazy, meaning they are not executed until a terminal operation is invoked.

Terminal operations produce a result or side-effect and trigger the processing of the stream pipeline.

• Intermediate operations: filter, map, sorted, distinct, limit
• Terminal operations: forEach, collect, reduce, count, anyMatch

Example: Using Streams to Process a List

Let's see a simple example that filters and transforms a list of strings using streams.