Object Oriented Design Patterns

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What are design patterns

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General, reusable solutions to commonly occuring problems in software design. A description or template for how to solve a problem that can be used in many different situations.

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Advantages of a design pattern

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Speed up the development process. Helps to prevent subtle issues that can cause major problems. Improves readability of the code. Provides patterns for solving problems.

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Three categories of design patterns

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Creational - Focuses on how objects are created.

Structural - Focuses on how objects are interconnected.

Behavioral - Focuses on objects that handle particular types of behavior.

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Strategy Pattern

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Defines a family of algorithms, encapsulates each one, and makes them interchangeable.

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Observer Pattern

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

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Decorator Pattern

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Attaches additional responsibilities to an object dynamically. [pattern] provide a flexible alternative to subclassing for extending functionality.

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Factory Method Pattern

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Defines an interface for creating an object, but lets subclasses decide which class to instantiate. [pattern] lets a class defer instantiation to subclasses.

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Abstract Factory Pattern

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Provides an interface for creating families of related or dependent objects without specifying their concrete classes.

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Singleton Pattern

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Ensures a class has only one instance, and provides a global point of access to it.

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Command Pattern

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Encapsulates a request as an object, thereby letting you parameterize other objects with different requests, queue or log requests, and support undoable operations.

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Adapter Pattern

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Converts the interface of a class into another interface the client expect. [pattern] lets classes work together that couldn't otherwise because of incompatible interfaces.

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Facade Pattern

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Provides a unified interface to a set of interaces in a subsystem. [pattern] defines a higher-level interface that makes the subsystem easier to use.

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Template Method Pattern

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Defines the skeleton of an algorithm in a method, deferring some steps to subclasses. [pattern] lets sub-classes redefine certain steps of an algorithm without changing the algorithm's structure.

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Iterator Pattern

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Provides a way to access the elements of an aggregation object seqentially without exposing its underlying reresentation.

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Composite Pattern

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Allows you to compose objects into tree structures to represent part-whole hierarchies. [pattern] lets clients treat individual objects and compositions of objects uniformly.

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State Pattern

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Allows an object to alter its behavior when its internal state changes. The object will appear to change its class.

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Proxy Pattern

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Provides a surrogate or place holder for another object to control access to it.

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Bridge Pattern

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Decouples an abstraction from its implementation so that the two can vary independently.

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Builder Pattern

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Separates the construction of a complex object from its representation so that the same construction process can create different representations.

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Chain of Responsibility Pattern

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Avoids 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.

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Flyweight Pattern

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Uses sharing to support large numbers of fine-grained objects efficiently.

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Interpreter Pattern

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Defines a representation of a grammar for a language along with an interpreter that uses the representation to interpret sentences in the language.

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Mediator Pattern

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Defines an object that encapsulates how a set of objects interact. [pattern] promotes loose coupling by keeping objects from referring to each other explicitly, and lets you vary their interaction independently.

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Momento Pattern

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Without violating encapsulation, captures and externalizes an object's internal state so that the object can be restored to this state later.

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Prototype Pattern

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Specifies the kinds of objects to create using a prototypical instance, and create new objects by coping this prototype.

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Visitor Pattern

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Represents an operation to be performed on the elements of an object structure. [pattern] lets you define a new operation without changing the classes of the elements on which it operates.