Stream API

A Stream is a sequence of objects that supports various methods which can be pipelined to produce the desired result.

[!NOTE] A Stream is not a data structure. It takes input from Collections, Arrays, or I/O channels.

Key Operations

1. Intermediate Operations (Returns a Stream)

• filter(): Selects elements based on a condition.
• map(): Transforms elements.
• sorted(): Sorts the stream.

2. Terminal Operations (Returns a Result)

• collect(): Gathers results back into a Collection.
• forEach(): Iterates over elements.
• reduce(): Reduces elements to a single value.
• count(): Counts the elements.

Example Usage

List<String> names = Arrays.asList("Alice", "Bob", "Charlie", "David");

// Filter names starting with 'C'
List<String> result = names.stream()
    .filter(name -> name.startsWith("C"))
    .collect(Collectors.toList());

System.out.println(result); // [Charlie]

Interactive Code

Analyze a list of numbers!

Quiz

Next Steps

NullPointerExceptions are the worst. Java 8 gave us a weapon against them: Optional Class.