# Hi, I'm Sven Woltmann.

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## Discover the HappyCoders Blog

Stay up-to-date with the latest tips about Java programming and closely related DevOps topics.

## Big O Notation and Time Complexity – Easily Explained

by Sven Woltmann – May 28, 2020

The big O notation¹ is used to describe the complexity of algorithms. On Google and YouTube, you can find numerous articles and videos explaining the big O notation. But to understand most of them (like this Wikipedia article), you should have studied mathematics as a preparation. ;-) That’ s why, in this article, I will

## Java Queue, Deque, and Stack: Ultimate Guide

by Sven Woltmann – April 8, 2020

Sooner or later, Java developers have to deal with the abstract data type queue, deque, and stack. This article explains the basic functionality of these data structures and gives a detailed overview of all implementations available in the JDK. Numerous code examples should make it easier for you to understand. In detail, the article answers

## How to switch Java versions in Windows (updated 03/2020 for Java 14)

by Sven Woltmann – March 17, 2020

As a Java programmer, I work on various projects based on different Java versions, especially since the transition to the six-month release cycle. From time to time, I also have a piece of Java code that I want to try out on different Java versions – on the command line without having to click through

## Deep Reflection: How to Hack Integer and String

by Sven Woltmann – March 11, 2020

I am currently reading the book “The Pragmatic Programmer” by Andrew Hunt and David Thomas. In this book, the authors give the following task: Which of these “impossible” things can happen? […]3. In C++: a = 2; b = 3; if (a + b != 5) exit(1); […] One of the correct answers is 3.

## Java ByteBuffer: How to use flip() and compact()

by Sven Woltmann – February 26, 2020

In this article, I show you, using an example, how the Java ByteBuffer works, and what precisely the Methoden flip() and compact() do. The article answers the following questions: What is a ByteBuffer, and what do you need it for? How do you create a ByteBuffer? What do the values position, limit, and capacity mean?

## Java files, part 6: FileChannel, ByteBuffer, Memory-mapped I/O, Locks

by Sven Woltmann – February 26, 2020

The previous five parts of this article series covered reading and writing files, directory and file path construction, directory and file operations, and writing and reading structured data. In today’s part, I explain the NIO classes FileChannel and ByteBuffer introduced in Java 1.4 with JSR 51 (“New I/O APIs for the JavaTM Platform”). Moreover, I

Working with Sven really leveled up my Java and development skills! He provided invaluable guidance in all aspects of development, including concurrency, performance, reliability, and DevOps. Sven's focus on clean architecture meant our applications were simple to maintain and extend. He's always on the cutting edge of Java developments and is a pleasure to work with.

Matt Schultz Software Engineer at HappyCo

I have worked with Sven for over seven years, and I have to say that he stands out among the Java developers that are around today. Sven's superb attention to detail and vast technical knowledge always provided top-quality, thoughtful, and professional outcomes in any work.

With Sven's excellent mentoring and guidance ability, I gained high impact skills in solving complex problems and reached a new level as a developer. I highly recommend him to anyone who is looking for an efficient, talented, and skilled programmer!

Daniil Tomilow Senior Software Engineer Frontend at RatePAY

On a professional level, Sven and I are connected by more than 20 years, several company foundations, and the implementation of some very innovative ideas in the internet sector. Sven not only had the hat of the CTO but also of the software architect and lead developer. Also, the management of larger teams has been part of his tasks.

If you want to summarize Sven's performance and get to the point, I can only think of a quote from a very well-known business angel who once said: "Sven's software is not software. It is a piece of art".

Fabien Röhlinger Managing Director at NextPIT GmbH

I had the pleasure of working with Sven for more than a year. Working with Sven means each day you learn a little more. A manager whose ability to handle multiple projects was unlikely any I had seen before and made a dramatic increase in the productivity level of our company.

Whenever I have questions or concerns, Sven responds right away and even follows up later in the week or month to make sure my issues have been resolved. His patience and willingness to help me motivated me to do the best job I can.

"Genuine expertise" is the phrase that comes to my mind when I think about Sven.

Chhavi Jain Quality Assurance Test Engineer at Delivery Hero