Design patterns provide general solutions or flexible way to solve common design problems. Design Patterns in object oriented world is reusable solution to common software design problems which occur again and again in real world application development. It is a template or description for how to solve a problem which can be used in many different situations.
23 patterns are grouped into three main categories :
Creational Design Pattern
Factory Method
Abstract Factory
Builder
Prototype
Singleton
Structural Design Patterns
Adapter
Bridge
Composite
Decorator
Façade
Flyweight
Proxy
Behavioral Design Patterns
Chain of Responsibility
Command
Interpreter
Iterator
Mediator
Memento
Observer
State
Strategy
Template Method
Visitor
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Creational Patterns
1. Factory Method
Factory Method define an interface for creating an object, but let sub-classes decide which class to instantiate. Factory Method lets a class defer instantiation to sub-classes.
2. Abstract Factory
Abstract Factory provide an interface for creating families of related or dependent objects without specifying their concrete classes.
3. Builder
Builder separate the construction of a complex object from its representation so that the same construction process can create different representations.
4. Prototype
Prototype specify the kind of objects to create using a prototypical instance, and create new objects by copying this prototype.
5. Singleton
Singleton pattern can be implemented interfaces. It helps to hide dependencies. Singleton ensure a class has only one instance and provide a global point of access to it. It provides a single point of access to a particular instance, so it is easy to maintain.
Structural Patterns
6. Adapter
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.
7. Bridge
Bridge decouple an abstraction from its implementation so that the two can vary independently.
8. Composite
Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly.
9. Decorator
Decorator attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to sub-classing for extending functionality.
10. Facade
Facade provide a unified interface to a set of interfaces in a subsystem. Façade defines a higher-level interface that makes the subsystem easier to use.
11. Flyweight
Flyweight use sharing to support large numbers of fine-grained objects efficiently.
12. Proxy
Proxy provide a surrogate or placeholder for another object to control access to it.
Behavioral Patterns
13. Chain of Responsibility
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.
14. Command
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.
16. Iterator
Iterator provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.
17. Mediator
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.
18. Memento
Without violating encapsulation, capture and externalize an object's internal state so that the object can be restored to this state later.
19. Observer
Observer define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
20. State
State allow an object to alter its behavior when its internal state changes. The object will appear to change its class.
21. Strategy
Strategy define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.
22. Template Method
Define the skeleton of an algorithm in an operation, deferring some steps to sub-classes. Template Method lets sub-classes redefine certain steps of an algorithm without changing the algorithm's structure.
23. Visitor
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.
