Many Java developers still write loops – not because streams are inferior, but because they were never properly explained. flatMap(), Collectors, reduce(), and Lazy Evaluation: these concepts make data processing in Java clearer, shorter, and more maintainable.
In just one day, this course brings your team up to the level the Java Streams API makes possible – clearly explained and directly applicable.
In this one-day course, you’ll learn the fundamentals of the Java Streams API – with clear explanations, practical examples, and lots of hands-on exercises.
You’ll discover how Streams differ from traditional Collections – and why they’re such a powerful tool for modern data processing in Java.
Through practical scenarios, we’ll explore the structure of a stream pipeline – from the data source, through intermediate operations like map(), filter(), and flatMap(), to final processing with collect(), reduce(), and collecting results into a map with toMap(). You’ll learn when each operation makes sense – and where the typical pitfalls lie.
A special focus is placed on understanding the underlying concepts: What happens when? What actually gets executed – and what doesn’t? What exactly does Lazy Evaluation mean – and what do you need to watch out for in everyday project work?
By the end of the day, you’ll be able to confidently use streams, aggregate complex data operations with collectors, combine values with reduce(), and apply functional programming effectively in your projects.
👉 Already familiar with streams and ready to go deeper? Check out Java Streams Advanced – Gatherers, Spliterators & More.
👉 Want to cover the full range of the Stream API in one go? Then the combined course Java Streams Basics + Advanced is ideal for you.
💡 Not sure yet whether streams are the right fit for you? My article Java Streams (with Examples) gives you a taste of what the Stream API can do.
This course is designed for Java developers who want to systematically learn streams and functional programming from the ground up.
Whether you’ve avoided streams, only scratched the surface, or want to refresh your knowledge – this course will help you build a solid foundation for productive use in real-world projects.
If you’ve preferred traditional loops because streams seemed too abstract: after this course, you’ll know when and how to use them effectively.
The course alternates between short theory segments, hands-on code examples, and interactive exercises – so you learn the fundamentals of the Stream API in a well-structured and practical way.
Functional Programming in Java:
Consumer, Supplier, Function, Predicate, etc.)Stream Basics:
IntStream, LongStream, DoubleStreamIntermediate Operations Deep Dive:
map(), flatMap(), filter()distinct(), sorted(), limit(), skip()peek() – used correctlyTerminal Operations:
collect() – the most versatile terminal operatortoList(), toSet(), toMap() – stream to map made easyStream.toList() and how it differs from Collectors.toList()forEach(), forEachOrdered()reduce() for aggregationsfindFirst(), findAny() – understanding and correctly using the Optional return typeallMatch(), anyMatch(), noneMatch()The agenda isn’t set in stone: we can align the focus, date, and format with your team.
Request now – no obligationI’ve been working with Java for 30 years – as a developer, CTO, trainer, author, and speaker.
In that time, I’ve helped companies modernize complex Java systems, write performant code, and develop their teams sustainably.
With HappyCoders.eu, I’ve built one of the most widely read Java blogs in the German-speaking world, and I regularly speak at conferences and user groups.
My goal: to teach complex topics in a way that is understandable, practical, and immediately applicable.
100 % of the participants who answered would recommend my training – 82 % without reservation.
More about meSven Woltmann of HappyCoders visited us to test and understand the new features around Java 25 together.
For two days, we worked intensively on Unnamed Variables & Patterns, Stream Gatherers, Scoped Values, the Foreign Function & Memory API, and performance topics such as virtual threads without pinning.
A big thank you to Sven for the excellent preparation, the clear didactics, and the deep technical expertise. That was a training exactly to our taste.
Content and presentation nearly flawless. I enjoyed listening throughout, learned new things, and had fun doing it.
Your confidence in answering questions along the way was impressive.
I found the trainer easy to listen to, and it never got boring. I understood the explanations well. Sven answered questions quickly and corrected errors in the worksheets on the spot.
A comprehensive training, with a trainer who knows what he is talking about. And when he doesn’t know, he looks it up right away or follows up with the answer shortly after.
Anyone who understands Java can easily follow this training. The exercises are well thought out and focused on the essentials.
A knowledgeable trainer. Good structure, practical examples. Compact, and the concepts get explained. Good, comprehensible exercises.
The overall package was very coherent and always tailored to us.
A good, in-depth overview of all relevant Java features since Java 8, and the opportunity to try all of these features out yourself.
The talk was broken up by fitting exercises. Good presentation. Our questions were taken up.
Very practical and good exercise examples.
Quick to respond to questions – a very flexible trainer.
A compact overview of how Java has evolved. A lot of input, much of which you can apply directly.
Very good repo with explanations + exercises in one place.
Pace + depth: top-notch. A very pleasant mix of theory and practice.
A complex topic broken down superbly.
All the important news from Java 9–25 was well explained.
This training can only be booked for teams. If you’d like to attend as an individual, I offer two courses (in German) through ppedv:
Both are possible: I can come to your company for an on-site training – anywhere in Germany, Austria, and Switzerland – or we run the training online, usually via Zoom.
I recommend a maximum of 12 participants per training – that way I can give everyone individual attention. There is no minimum: I charge per training, not per person.
The easiest way is the request form or an email to training@happycoders.eu. Right after submitting, you can book a video call via Calendly, where we discuss the details. You’ll then receive a concrete offer from me.
You should bring basic Java knowledge – that is, classes, interfaces, collections, and generics. Experience with lambda expressions or functional programming is not a must: those are the first topics we’ll work through together.
All participants need an up-to-date IDE with at least Java 17 – I use IntelliJ IDEA myself. Java 17 or later should also be installed in the terminal, as we’ll run some of the exercises there.
A training day consists of four 90-minute modules – six hours of net training time in total. Each module alternates between theory and practice two to three times, so you apply what you’ve just learned directly to code. There’s a short break between the first and second and between the third and fourth module, and a longer lunch break between modules two and three. We align the exact schedule with your working hours – that’s flexible.
About half theory, half practice: a short theory phase is followed directly by applying it to code – with examples from real projects. Listening alone doesn’t help much; the knowledge has to be used immediately for it to stick.
Yes – shortening topics, weighting them differently, changing the order, or combining content from different courses: I’m happy to adapt the agenda to your team. Since that means reworking the training materials, it involves extra effort – I’ll prepare an individual offer for you.
We usually use Zoom. If you prefer your own platform – for example, Microsoft Teams or Google Meet – I’m happy to work with that. Just let me know in advance.
Yes. Before the training, you’ll receive the exercises as a Git repository so you can get started right away. After the training, you’ll also receive the slides – including all solutions to the exercises.
Yes. All participants receive a certificate of attendance after the training.
Travel expenses are charged as a flat rate – depending on the training location and the number of overnight stays required. The exact amount is part of the individual offer I’ll send you.
Yes. For multiple booked trainings or follow-up bookings, I can offer a volume discount. We’ll discuss this in the video call, and I’ll include it in the offer.
Just write to me – I usually reply within one business day.
Or book a free video call right away, and we’ll discuss everything important.