Design Patterns in Kotlin

This book is a comprehensive practical guide to applying classic design patterns (GoF) in the Kotlin language. Unlike abstract theoretical descriptions, the material is built on real-world examples and tasks that every developer encounters. You will not only learn how a particular pattern works, but also understand when and why to use it, and when it is better to avoid it.

The author systematically covers all three groups of patterns: creational (Singleton, Factory, Builder, Prototype), structural (Adapter, Decorator, Facade, Proxy), and behavioral (Strategy, Observer, Command, State). Each pattern is examined through the lens of modern Kotlin features: lambda expressions, extension functions, sealed classes, coroutines, and null-safety. You will see how the language allows you to implement classic solutions more concisely and safely than in Java.

Special attention is paid to the SOLID principles and how patterns help adhere to them. The book teaches not just copying code, but thinking architecturally: identifying volatile parts of a system, building flexible connections between components, and avoiding anti-patterns. Each chapter contains not only implementation examples but also a comparison of alternative approaches, trade-off analysis, and refactoring recommendations.

Who this book is for:

• Kotlin developers (Android, backend, multiplatform) looking to improve code quality.
• Java programmers transitioning to Kotlin and seeking idiomatic ways to apply patterns.
• Tech leads and architects designing scalable and maintainable systems.
• Students and junior developers learning the fundamentals of object-oriented design.

What you will learn:

• How 23 classic GoF patterns are implemented in Kotlin, leveraging its unique features.
• How to combine patterns to solve complex architectural problems.
• How to avoid common mistakes and unnecessary code complexity.
• How patterns relate to the SOLID, DRY, KISS, and YAGNI principles.
• How to test code built using patterns.

The book is written in a lively, accessible language and is suitable both for sequential study and for use as a reference. All code examples are tested and accompanied by detailed comments. After reading, you will be able to confidently design flexible, easily extensible applications in Kotlin that do not "fall apart" when new requirements emerge.