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Design patterns are recurring solutions to software design problems you find again and again in real-world application development. Patterns are about design and interaction of objects, as well as providing a communication platform concerning elegant, reusable solutions to commonly encountered programming challenges.
The Gang of Four (GoF) patterns are generally considered the foundation for all other patterns.
They are categorized in three groups:
1) Creational
2) Structural
3) Behavioral.
Creational Patterns:
These patterns provide solutions that encapsulate the logic to instantiate or create objects.
Abstract Factory
Creates an instance of several families of classes
Builder
Separates object construction from its representation
Factory Method
Creates an instance of several derived classes
Prototype
A fully initialized instance to be copied or cloned
Singleton
A class of which only a single instance can exist
Structural Patterns:
These patterns describe how you can build increasingly complex and powerful classes and objects by combining classes or objects (respectively) together into larger entities.
Adapter
Match interfaces of different classes
Bridge
Separates an object’s interface from its implementation
Composite
A tree structure of simple and composite objects
Decorator
Add responsibilities to objects dynamically
Facade
A single class that represents an entire subsystem
Flyweight
A fine-grained instance used for efficient sharing
Proxy
An object representing another object
Behavioral Patterns:
Behavioral patterns provide solutions that control how an object or objects behave at run-time. These patterns focus on how objects communicate or interact, and how classes are assigned responsibilities.
Chain of Resp.
A way of passing a request between a chain of objects
Command
Encapsulate a command request as an object
Interpreter
A way to include language elements in a program
Iterator
Sequentially access the elements of a collection
Mediator
Defines simplified communication between classes
Memento
Capture and restore an object's internal state
Observer
A way of notifying change to a number of classes
State
Alter an object's behavior when its state changes
Strategy
Encapsulates an algorithm inside a class
Template Method
Defer the exact steps of an algorithm to a subclass
Visitor
Defines a new operation to a class without change
