Design Patterns Using Java

All 23 design patterns from the famous Gang of Four book "Design Patterns: Elements of Reusable Object Oriented Software".

GoF Design Patterns are divided into three categories:

1. Creational: These design patterns deal with the creation of an object.
2. Structural: These design patterns deal with the class structure such as Inheritance and Composition.
3. Behavioral: These design patterns provide solution for the better interaction between objects, how to provide loose coupling, and flexibility to extend easily in future.

Creational Design Patterns

Pattern Name	Description
Singleton	The singleton pattern restricts the initialization of a class to ensure that only one instance of the class can be created.
Factory	The factory pattern takes out the responsibility of instantiating a object from the class to a Factory class.
Abstract Factory	Allows us to create a Factory for factory classes.
Builder	Creating an object step by step and a method to finally get the object instance.
Prototype	Creating a new object instance from another similar instance and then modify according to our requirements.

Structural Design Patterns

Pattern Name	Description
Adapter	Provides an interface between two unrelated entities so that they can work together.
Composite	Used when we have to implement a part-whole hierarchy. For eg, a diagram made of other pieces such as circle, square, etc.
Proxy	Provide a surrogate or placeholder for another object to control access to it.
Flyweight	Caching and reusing object instances, used with immutable objects. For example, string pool.
Facade	Creating a wrapper interfaces on top of existing interfaces to help client applications.
Bridge	Decouples the interfaces from implementation and hides the implementation details from the client program.
Decorator	Modifies the functionality of an object at runtime.

Behavioral Design Patterns

Pattern Name	Description
Template Method	used to create a template method stub and defer some of the steps of implementation to the subclasses.
Mediator	used to provide a centralized communication medium between different objects in a system.
Chain of Responsibility	used to achieve loose coupling in software design where a request from the client is passed to a chain of objects to process them.
Observer	useful when you are interested in the state of an object and want to get notified whenever there is any change.
Strategy	used when we have multiple algorithm for a specific task and client decides the actual implementation to be used at runtime.
State	used when an Object change it’s behavior based on it’s internal state.
Interpreter	defines a grammatical representation for a language and provides an interpreter to deal with this grammar.
Iterator	used to provide a standard way to traverse through a group of Objects.
Memento	used when we want to save the state of an object so that we can restore later on.