Java Design Patterns. 23 Proven Solutions for Common Problems

The book "Design Patterns in Java" is a practical guide to applying 23 classic design patterns (GoF) in the context of the Java language. The author, Alexey Petrov, a Senior Java Developer with 10 years of experience, systematizes the experience of creating scalable and maintainable applications.

What the book is about

The material covers all three groups of patterns:

• Creational — Singleton, Factory Method, Abstract Factory, Builder, Prototype. How to flexibly manage object creation without binding to specific classes.
• Structural — Adapter, Bridge, Composite, Decorator, Facade, Proxy, Flyweight. How to assemble classes into large structures while maintaining flexibility.
• Behavioral — Chain of Responsibility, Command, Iterator, Mediator, Memento, Observer, State, Strategy, Template Method, Visitor. How to distribute responsibilities between objects.

Each pattern is analyzed using a unified scheme: problem → UML diagram → Java implementation → real-world example (working with databases, web services, UI). A separate chapter is dedicated to anti-patterns and typical mistakes when applying patterns.

Who this book is for

• Junior Developers — will understand how to write code that doesn't "break" with changes.
• Middle Developers — will systematize their knowledge and learn to combine patterns.
• Senior Developers and Architects — will find advanced techniques (e.g., implementing Visitor via reflection or Thread-safe Singleton via enum).

What you will learn

• How to distinguish correct pattern usage from a "golden hammer".
• How patterns relate to the SOLID and DRY principles.
• How to implement the Factory Method in a Spring context.
• Why the Java Stream API uses the Iterator pattern, and Swing uses Observer.
• How to avoid multithreading issues when using Singleton.
• How to refactor "spaghetti code" using Strategy and State.

Edition features

• Over 60 ready-made Java examples with comments.
• Pattern comparison: when to choose Decorator, and when Proxy.
• "Patterns vs. Frameworks" table (which patterns underlie Hibernate, Spring, JUnit).
• Self-assessment exercises after each chapter.

The book is suitable both for sequential reading and as a reference. You will learn not just to copy patterns, but to understand why they work and adapt them to your tasks. After reading, you will be able to confidently design application architecture that is easily maintainable and extensible.

Note: the book is oriented towards Java 8+, but the examples are compatible with Java 11 and 17.