Design Patterns

Synopsis

Capturing a wealth of experience about the design of object-oriented software, four top-notch designers present a catalog of simple and succinct solutions to commonly occurring design problems. Previously undocumented, these 23 patterns allow designers to create more flexible, elegant, and ultimately reusable designs without having to rediscover the design solutions themselves.

The authors begin by describing what patterns are and how they can help you design object-oriented software. They then go on to systematically name, explain, evaluate, and catalog recurring designs in object-oriented systems. With Design Patterns as your guide, you will learn how these important patterns fit into the software development process, and how you can leverage them to solve your own design problems most efficiently.

Each pattern describes the circumstances in which it is applicable, when it can be applied in view of other design constraints, and the consequences and trade-offs of using the pattern within a larger design. All patterns are compiled from real systems and are based on real-world examples. Each pattern also includes code that demonstrates how it may be implemented in object-oriented programming languages like C++ or Smalltalk.

Summary

Chapter 1: Introduction to Design Patterns

* Summary:
* Defines design patterns as reusable solutions to common software design problems.
* Lists the goals of using design patterns: code reuse, maintainability, and communication.
* Real Example:
* Singleton Pattern: Ensures that only a single instance of a class can exist. Used in logging systems or database connections.

Chapter 2: Creational Patterns

* Summary:
* Describes design patterns used to create objects in various scenarios.
* Includes patterns like Factory Method, Abstract Factory, Singleton, Builder, and Prototype.
* Real Example:
* Factory Method Pattern: Defines an interface for creating objects, but allows subclasses to alter the type of objects that will be created. Used in GUIs to create buttons or other widgets.

Chapter 3: Structural Patterns

* Summary:
* Addresses patterns that organize objects and classes into larger structures.
* Covers Bridge, Adapter, Proxy, Composite, Decorator, and Facade.
* Real Example:
* Decorator Pattern: Attaches additional responsibilities to an object dynamically. Used in GUI development to add scrollbars or borders to widgets.

Chapter 4: Behavioral Patterns

* Summary:
* Explores patterns that define how objects interact and communicate.
* Includes Command, Strategy, Observer, Iterator, Template Method, and State.
* Real Example:
* Command Pattern: Encapsulates a request as an object, allowing it to be queued, logged, or undone. Used in undo/redo functionality in text editors.

Chapter 5: Architectural Patterns

* Summary:
* Discusses high-level patterns that describe the overall structure and organization of a system.
* Covers MVC, MVP, Repository, and Mediator.
* Real Example:
* MVC (Model-View-Controller) Pattern: Separates the data, presentation, and control logic into distinct components. Used in GUI applications to allow multiple views of the same model.

Chapter 6: Structural Patterns for Concurrency

* Summary:
* Introduces patterns designed to handle concurrency and multithreading.
* Includes Reader/Writer, Monitor, Guarded Suspension, and Active Object.
* Real Example:
* Guarded Suspension Pattern: Allows a thread to suspend until an event has occurred, such as the completion of an asynchronous operation. Used in web servers to handle client requests.

Chapter 7: Advanced Concepts

* Summary:
* Discusses advanced topics related to design patterns, such as pattern reuse, anti-patterns, and frameworks.
* Covers Dependency Inversion, Dependency Injection, and Aspect-Oriented Programming.
* Real Example:
* Dependency Injection: Injects dependencies into an object instead of hardcoding them. This allows for greater flexibility and testability. Used in unit testing frameworks.