GoF Design Pattern Java

The book "Design Patterns: Elements of Reusable Object-Oriented Software" has 23 design patterns, which are grouped together as Gangs of Four Design Patterns.

One of the most well-liked books to understand design patterns was first published in 1994. Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides wrote the book. Because there were four creators, it was given the moniker "Gangs of Four" design patterns. Additionally, it was shortened to "GoF Design Patterns."

Types of GoF Design Patterns

Three categories make up the GoF Design Patterns:

Creational: Design patterns that deal with the production of an object are called creational patterns.

Structural: This category of design patterns focuses on concepts like composition and inheritance that relate to class structure.

Behavioural: Design patterns that are behavioral in nature offer solutions for better object-to-object communication, loose coupling, and future expansion flexibility.

Designs used in the creation

The category of creational design patterns has 5 patterns.

Pattern Name	Description
Singleton	In order to prevent the creation of more than one instance of a class, a singleton pattern restricts class initialization.
Factory	With the factory pattern, a Factory class instead of the class is in charge of creating new objects.
Abstract Factory	creates a Factory using factory classes, which is possible.
Builder	step-by-step creation of an object and a way to obtain the object instance.
Prototype	creating an entirely new object instance from such an existing one that is comparable and then modifying it to meet our needs.

Patterns for Structural Design

The Gangs of Four design patterns book lists 7 structural design patterns.

Pattern Name	Description
Adapter	It allows two unconnected entities to interact so they are able to work together.
Composite	It is used when a part-whole hierarchy needs to be implemented. For instance, a diagram is composed of additional elements like circles, squares, triangles, etc.
Proxy	It is used to restrict access to another object, create a substitute or stand-in for it.
Flyweight	It Ieveraging immutable objects and caching and reuse of object instances. Consider string pool.
Facade	It wraps existing interfaces in new interfaces to assist client applications.
Bridge	The bridge design pattern is utilized to hide actual implementation details from of the client program and decouple their interfaces from implementation.
Decorator	The decorator design pattern is employed to alter an object's functionality in real-time.

Patterns for Behavioral Design

The GoF design patterns list eleven behavioral design patterns.

Pattern Name	Description
Template Method	Deferring some of the implementation tasks to the subclasses through the usage of a template method.
Mediator	A mediator is a device that offers a centralized communication channel between various system elements.
Chain of responsibility	A request from either the client is delivered to a chain of objects to be processed as part of the Chain of Responsibility technique used in software design to promote loose coupling.
Observer	When you're interested in an object's status and want to be notified whenever it changes, an observer is handy.
Strategy	When there are several algorithms available for a given task and the client chooses the actual implementation that will be used at runtime, the strategy pattern is employed.
Command	It is used to implement loose coupling in a request-response model, utilize the Command Command Pattern.
state	When an object changes its behavior based on its internal state, the state design pattern is applied.
Visitor	When we need to conduct an operation on a collection of objects that are all of a similar type, we utilize the visitor pattern.
Interpreter	explains how to express a language's grammar and offers an interpreter to deal with it.
Iterator	An iterator was once used to offer a common method of browsing through a collection of objects.
memento	When we want to store an object's state for subsequent restoration, we utilize the memento design pattern.

Conclusion

groups of the fundamental design patterns used in programming are built on four patterns. On top of these design patterns, numerous others are constructed for various requirements.

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