Design Patterns

About / Introduction

Design patterns are typical solutions to common problems in software design.
Each pattern is like a blueprint that you can customize to solve a particular design problem in your code.
Benefits of patterns:
- Patterns are a toolkit of solutions to common problems in software design.
- They define a common language that helps your team communicate more efficiently.
Classification:
- Design patterns differ by their complexity, level of detail and scale of applicability. In addition, they can be categorized by their intent and divided into three groups.
- The most basic and low-level patterns are often called idioms. They usually apply only to a single programming language.
- The most universal and high-level patterns are architectural patterns. Developers can implement these patterns in virtually any language. Unlike other patterns, they can be used to design the architecture of an entire application.
- All patterns can be categorized by their intent, or purpose. Here we'll discuss the three main groups of patterns:
  - 1. Creational:
    - The design patterns that deal with the creation of an object.
  - 2. Structural:
    - These design patterns deals 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 lose coupling, and flexibility to extend easily in future.

Design Patters

Category	Design Pattern	Info	Example
Creational D.P.		There are 5 design patterns in Creational Design Pattern category.
	Singleton	Restricts the initialization of a class to only one instance of the class per JVM.
	Factory	Takes out the responsibility of instantiating a object from the class to a Factory class.
	Absstract 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 D.P.		There are 7 design patterns defined in Structural Design Pattern category.
	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 example, a diagram made of other pieces such as circle, square, triangle, 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.	Java String pool
	Faced	Creating a wrapper interfaces on top of existing interfaces to help client applications.
	Bridge	The bridge design pattern is used to decouple the interfaces from implementation and hiding the implementation details from the client program.
	Decorator	The decorator design pattern is used to modify the functionality of an object at runtime.

Behavioral D.P.		There are 11 design patterns defined in Behavioral Design Pattern category.
	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	Get notified whenever there is any change in the state of an object.
	Strategy	Used when we have multiple algorithm for a specific task and client decides the actual implementation to be used at runtime.
	Command	Command Pattern is used to implement lose coupling in a request-response model.
	State	State design pattern is used when an Object change it’s behavior based on it’s internal state.
	Visitor	Visitor pattern is used when we have to perform an operation on a group of similar kind of Objects.
	Interpretor	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.

References:

Design Patterns

About / Introduction

Design Patters

------ End ------