Java 8 Stream API – Basics

Java 8 introduced a powerful feature called Stream API, found in the package:

import java.util.stream.*;

What is a Stream?

A Stream is a sequence of elements that supports functional-style operations to process data. It works primarily with collections like List, Set, etc.

Think of a stream as a conveyor belt that allows you to:

• Filter
• Transform
• Collect
• Iterate
• Convert data

Why Use Streams?

• Removes the need for manual loops
• Efficient and readable
• Helps write clean and declarative code
• Supports parallel processing

Key Difference

Concept	Purpose
Collection	Used to store a group of objects
Stream	Used to process those objects

How to Create a Stream

You can create a stream from a collection like this:

Stream<T> s = collection.stream();

• collection is any List, Set, etc.
• .stream() creates a Stream object

Prerequisites

Before learning Streams, you should be familiar with:

• Lambda expressions
• Method references
• Optional class (introduced in Java 8)

Components of a Stream

1. Sequence of Elements

• A stream works with a sequence of data (like items in a list)

2. Source

• The source can be a collection, array, or I/O channel

3. Aggregate Operations

• Operations like filter(), map(), collect(), etc.

4. Pipelining

• Multiple operations can be chained together (like filters and maps)

5. Internal Iteration

• Stream handles looping internally, unlike traditional for loops

Important Notes

• Streams belong to the package: java.util.stream
• They do not store data; they only process it
• They support lazy evaluation — operations are only performed when necessary