Design Patterns in Java: A Practical Guide

The book "Java Design Patterns" is a practical guide to applying the 23 classic patterns described by the "Gang of Four." The author, Alexey Smirnov, a Senior Java Developer with 12 years of experience, shares not only theory but also real-world cases from commercial development.

What is this book about?

The book covers all three groups of patterns:

• Creational (Singleton, Factory Method, Abstract Factory, Builder, Prototype) — how to manage object creation;
• Structural (Adapter, Decorator, Proxy, Facade, Composite, Bridge, Flyweight) — how to build flexible relationships between classes;
• Behavioral (Observer, Strategy, Command, Iterator, Mediator, Memento, State, Template Method, Visitor, Chain of Responsibility, Interpreter) — how to organize interaction between objects.

Who is this book for?

• Junior Developers (1-2 years of experience) — systematize your knowledge and stop reinventing the wheel;
• Middle Developers — learn to choose the right pattern for a task and avoid anti-patterns;
• IT Students — understand how OOP theory is applied in practice.

What will you learn?

• How each pattern solves a specific design problem;
• How to read and build UML class diagrams;
• The difference between similar patterns (e.g., Strategy vs State);
• How to combine patterns in real projects;
• How to avoid common mistakes when implementing patterns (anti-patterns);
• How patterns are applied in modern Java frameworks (Spring, Hibernate).

Book structure

Each pattern is analyzed using a single template:

1. Problem — a real situation from development;
2. Solution — UML diagram and full code in Java 17+;
3. Applicability — when to use the pattern and when not to;
4. Practice — an example from a web application, game, or API;
5. Summary — pros, cons, and relationships with other patterns.

Why should you read it?

The book is written in simple language without excessive academicism. All examples can be run immediately in IntelliJ IDEA. At the end of each chapter, there are exercises for self-assessment. This is not a reference book, but a full-fledged textbook that will help you move to a new level in Java programming.

It is ideal both for self-study and for preparing for technical interviews. Design patterns are a must-have for any Java developer aiming for a Middle position and above.