Why 0.1 + 0.2 isn't 0.3, when double is fine, when BigDecimal is mandatory, and when fixed-point long is fastest. A beginner-to-advanced guide to number precision in Java — with runnable code, real output, a benchmark, rounding modes, MathContext, and a decision table.
A practical Spring Framework 6 to 7 migration guide covering the Jakarta EE 11 baseline, removed and deprecated APIs, AOT and GraalVM changes, BeanRegistrar and proxy lifecycle changes, JSpecify null safety, testing and security implications, an upgrade checklist, and an AI prompt to scan your project.
A beginner-to-advanced guide to structured concurrency in Java (JDK 25/26). Learn StructuredTaskScope, Joiners (allSuccessfulOrThrow, anySuccessfulOrThrow, race), timeouts, custom joiners, failure handling, thread-dump observability, and how it compares to CompletableFuture — with runnable code, real output, and a diagram.
Learn the Interpreter design pattern in Java by building a working math expression evaluator. Understand abstract syntax trees, terminal vs. non-terminal expressions, and where this pattern appears in SQL engines, regex, and Spring SpEL.
Complete reference for all 23 Gang of Four design patterns implemented in Java 17. Each pattern has a dedicated post with beginner-to-advanced coverage, full runnable code, UML diagram, and console output. Creational, Structural, and Behavioral patterns with real-world examples and JDK cross-references.
The Visitor pattern lets you add new operations to a class hierarchy without modifying it. Each operation is a separate Visitor class; elements accept visitors via double dispatch. Complete Java guide: shape hierarchy with AreaCalculator and PerimeterCalculator visitors, double dispatch explained, when Visitor beats a switch statement, and when it's overkill.
The Template Method pattern defines the skeleton of an algorithm in a base class and lets subclasses fill in the steps — without changing the overall structure. Complete Java guide: data migration pipeline with invariant skeleton, overridable hooks, and the Hollywood Principle. Includes comparison with Strategy and when to use each.
The Strategy pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable at runtime. No more switch statements for algorithm selection. Complete Java guide: sorting strategy with BubbleSort/MergeSort/QuickSort, runtime selection, Java 8 functional shortcut with Comparator, and when Strategy is overkill.
The State pattern lets an object change its behaviour when its internal state changes — as if the object changed its class. Eliminate sprawling if-else state machines. Complete Java guide: traffic light example, state-driven transitions, how State differs from Strategy, vending machine walkthrough, and when to use enums vs State objects.
The Observer pattern defines a one-to-many dependency: when one object changes state, all dependents are notified automatically. Complete Java guide: stock price alert system, dynamic subscribe/unsubscribe, push vs pull notification models, java.util.Observable pitfalls, PropertyChangeListener, reactive extensions, and thread-safety considerations.