A software engineering journal
Notes on Java, architecture, and the tools we use to build better software. Written by Andrés Tascón.
01 / The journal
A practical guide to testing strategy for Java backend systems — from unit tests with JUnit and Mockito, to integration tests with Testcontainers, contract tests with Pact, and concurrency tests that catch race conditions. Includes a complete fintech wallet example.
Scoped Values are production-ready, object headers just got smaller, and you can finally write code before super(). Here's why Java 25 is the LTS release you shouldn't skip.
A practical guide to building Model Context Protocol servers — covering tools, resources, and prompts, plus the rules that separate production servers from proof-of-concepts.
A practical guide to Atomicity, Consistency, Isolation, and Durability — with SQL examples and a bank transfer walkthrough showing all four properties in action.
Understand what hashcodes really are, how HashMap lookups work under the hood, and why the hashCode-equals contract is the foundation of every cache and collection in your application.
Learn what immutability really means in Java, how to make objects immutable (the five rules), why Strings work the way they do, and every way to make collections immutable — with tradeoffs.
02 / Put it into practice
60 questions to sharpen your understanding of the ideas behind the code.