Practical utilities
The article wraps up the "Design Pattern Dissection" series by showing how the 23 GoF patterns appear in JDK, Spring and MyBatis, clarifying the most confusing pattern pairs, warning against over‑design, and presenting a comprehensive map that links each pattern to the seven core design principles.
This article examines the three least‑used behavioral design patterns—Mediator, Visitor, and Interpreter—by explaining the problems each solves, showing core implementations with order‑page examples, highlighting their narrow applicability, common pitfalls, and why developers should often steer clear of them.
The article explains how the Iterator pattern, built into Java as Iterable and Iterator interfaces, lets you traverse any collection uniformly without exposing its internal structure, demonstrates the fail‑fast mechanism, and shows when custom collections should implement Iterable.
The article explains how the Command pattern encapsulates a request as an object, enabling storage, queuing, undo/redo, and decoupling between request senders and executors, with concrete Java examples and guidance on when the pattern is appropriate.
The article demonstrates how the State design pattern replaces tangled if‑else state checks with dedicated state classes, using an order lifecycle example to compare it with Strategy, explain role responsibilities, transition driving mechanisms, and guidelines for when to apply the pattern.
The article explains the Chain of Responsibility design pattern, showing how to replace tangled nested if‑checks in order‑validation logic with a series of independent handler objects linked together, and demonstrates its implementation, variations, real‑world uses in filters, interceptors, and guidelines for when the pattern is appropriate.
The article explains the Observer pattern by first showing the problems of hard‑coding post‑payment actions, then detailing how defining a subject, observer interface, and concrete observers decouples the system, discusses push vs pull notification models, and illustrates real‑world uses in Spring events, GUI listeners, and message queues.
The article explains the Template Method design pattern, showing how to lock a fixed process skeleton in a parent class while delegating variable steps to subclasses, contrasting it with the Strategy pattern and illustrating its use in real‑world frameworks.
This article walks through the full lifecycle of a Java class—from loading, verification, preparation, and resolution to initialization, usage, and unloading—explains active versus passive references, the parent‑delegation model, JDK 8‑to‑17 module‑system changes, and shows how to write a custom ClassLoader for class isolation.
The article explains how the Strategy design pattern solves the maintenance nightmare of tangled if‑else or switch statements by extracting each algorithm into its own strategy class, detailing the roles, selection mechanisms, Java examples, and when the pattern is appropriate.
