Java Design Patterns (2nd Edition)

This book (original English edition: Design Patterns in Java, 2nd Edition) is a hands-on companion to the classic GoF work Design Patterns. Rather than merely restating the intent and structure of the 23 patterns one by one, the author uses Java as the vehicle and, through a sample project with a complete business context—Oozinoz, a simulated factory system that manufactures fireworks and firecrackers—demonstrates each pattern in realistic modeling, coding, and refactoring situations. Readers can clearly see a design evolve from something that merely "runs" into something that can be changed and extended. The book regroups the 23 patterns into five categories: interface, responsibility, construction, operation, and extension. Each category is preceded by an introductory chapter that first clarifies the problems shared by patterns of that type: how to choose between interfaces and abstract classes, how to assign responsibilities and control visibility, construction techniques beyond constructors, making operations and algorithms polymorphic, and eliminating code "bad smells" guided by the Open-Closed Principle, the Liskov Substitution Principle, and the Law of Demeter. This classification differs from GoF's three-way division into creational, structural, and behavioral patterns, and is closer to the practical thought process of asking which group of patterns to look for when a particular problem arises. Each pattern chapter includes a UML class diagram and runnable Java code, along with several exercises that guide readers to experience the applicable boundaries and costs of the patterns through hands-on rewriting. Four appendices at the end provide an exercise guide, answers to all exercises, a description of the Oozinoz source code, and a UML quick reference, allowing readers to verify their work on their own. This edition is the 2nd edition of the simplified Chinese version of the book, translated by Zhang Yi and Shi Lei.