OOPs Design Patterns (Gang of four)

A list of design patterns, one must keep in arsenal :)

1. Strategy: Defines a family of algorithms, encapsulates each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients who use it.

2. Decorator: Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.

3. Factory Method: Define an interface for creating an object, but let the subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.

4. Observer: Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.

5. Chain of Responsibility: Avoid coupling the sender of a request to its receiver by giving more then one object a chance to handle the request. Chain the receiving objects and pass the request along the chain until an object handles it.

6. Singleton: Ensure a class only has one instance, and provide a global point of access to it.

7. Flyweight :Use sharing to support large numbers of fine-grained objects efficiently. A flyweight is a shared object that can be used in multiple contexts simultaneously. The flyweight acts as an independent object in each context; it’s indistinguishable from an instance of the object that’s not shared.

8. Adapter :Convert the interface of a class into another interface clients expect. Adapter lets classes work together that couldn’t otherwise because of incompatibility interfaces.

9. Façade : Provide a unified interface to a set of interfaces in a system. Façade defines a higher-level interface that makes the subsystem easier to use.

10. Template :Define a skeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithms structure.

11. Builder :Separate the construction of a complex object from its representation so that the same construction processes can create different representations.

12. Iterator :Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.

13. Composite :Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly.

14. Command :Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.

15. 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 lets you vary their interaction independently.

16. State :Allow an object to alter its behavior when its internal state changes. The object will appear to change its class.

17. Proxy :Provide a surrogate or placeholder for another object to control access to it.

18. Abstract Factory :Provide an interface for creating families of related or dependent objects without specifying their concrete classes.

19. Bridge :Decouple an abstraction from its implementation so that the two can vary independently.

20. Interpreter :Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language.

21. Memento :Without violating encapsulation, capture and externalize an object’s internal state so that the object can be restored to this state later.

22. Prototype :Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype.

23. 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.