What is Gang Of Four (GOF)?

Every Programmer should know! 📕

I was scrolling on LinkedIn & I saw a job post regarding an android developer. I saw the term GOF in job description. This term was completely new for me in my whole android dev career. 😅

I started finding curiously on Google What is GOF?

Then I got to know that there is a book that had been written by four authors about design patterns.

What is Gang Of Four?

The Gang Of Four are the authors of the Book “Design Patterns: Elements of Reusable Object-Oriented Software”.

It’s an important book describing twenty-three Object-Oriented Design Patterns & various development techniques. The four authors are:

1. Erich Gamma
2. Ralph Johnson
3. John Vlissides
4. Richard Helm

Overview

I am not gonna describe complete book here but a small picture to develop your interest in reading this book.

For better understanding, Gang Of Four described each design pattern with a UML diagram by taking real-world examples with coding.

They categorized all design patterns into three categories.

1. Creational Patterns
2. Structural Patterns
3. Behavioral Patterns

#1) Creational Patterns

The first design pattern is the creational pattern. It provides ways to instantiate single objects or groups of related objects. There are five such patterns:

• Abstract Factory: Provide an interface for creating families of related or dependent objects without specifying their concrete classes.
• Builder: Separate the construction of a complex object from its representation so that the same construction process can create different representations.
• Factory Method: Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.
• Prototype: Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype.
• Singleton: Ensure a class only has one instance, and provide a global point of access to it.

#2) Structural Patterns

The second type of design pattern is the structural pattern. It provides a manner to define relationships between classes or objects.

• Adapter: Convert the interface of a class into another interface clients expect. Adapter lets classes work together that couldn’t otherwise because of incompatible interfaces.
• Bridge: Decouple an abstraction from its implementation so that the two can vary independently.
• Composite: Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly.
• Decorator: Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.
• Facade: Provide a unified interface to a set of interfaces in a subsystem. A facade defines a higher-level interface that makes the subsystem easier to use.
• Flyweight: Use sharing to support large numbers of fine-grained objects efficiently
• Proxy: Provide a surrogate or placeholder for another object to control access to it.

#3) Behavioral Patterns

The final type of design pattern is the behavioral pattern. It defines manners of communication between classes and objects.

• Chain Of Responsibility: Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. Chain the receiving objects and pass the request along the chain until an object handles it.
• Command: Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue, or log requests, and support undoable operations.
• Interpreter: Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language.
• Iterator: Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.
• Mediator: Define an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently.
• Memento: Without violating encapsulation, capture and externalize an object’s internal state so that the object can be restored to this state later.
• Observer: Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
• State: Allow an object to alter its behavior when its internal state changes. The object will appear to change its class
• Strategy: Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.
• Template Method: Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm’s structure.
• Visitor: Represent an operation to be performed on the elements of an object structure. Visitor lets you define a new operation without changing the classes of the elements on which it operates.

Further Reading:

Roadmap to Becoming a Successful Android Developer

Basic Skills Required to Become an Android Developer