Java Streams Examples

Article

The code refers to the following articles:

• English: Java Streams (with Examples)
• German: Java Streams (mit Beispielen)

Contents

All examples work on the same data model: the records Book and Author, the enum Genre, and the Library class with eleven public-domain classics.

Every class with a main() method is one chapter of the article and prints the outputs shown there. Run one with java -cp target/classes eu.happycoders.streams.<ClassName> after mvn compile:

• Ch1Intro – the same task as a loop and as a stream; the anatomy of a stream pipeline
• Ch2Lambdas – lambda expressions, method references, functional interfaces
• Ch3Sources – creating streams from collections, arrays, ranges, files, and generators
• Ch4Intermediate – filter(), map(), flatMap(), mapMulti(), distinct(), sorted(), limit(), skip(), takeWhile(), dropWhile(), peek(), gather()
• Ch5Terminal – forEach(), collect() and collectors, toList(), toArray(), reduce(), count(), min(), max(), findFirst(), anyMatch(), and the others
• Ch6Lazy – lazy evaluation: element-by-element processing, short-circuiting, stateful operations, single use
• Ch7Parallel – parallel streams
• Ch8Mistakes – common mistakes and how to avoid them

The code requires Java 25 or newer.

Additional Resources

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