| Scope | Creational | Structural | Behavioral |
|---|---|---|---|
| Class | Factory Method | Interpreter Template Method |
|
| Object | Abstract Factory Builder Prototype Singleton |
Adapter Bridge Composite Decorator Facade Proxy |
Chain Of Responsiblity Command Iterator Mediator Memento Flyweight Observer State Strategy Visitor |
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23 Popular Design patterns and their abstract definitions
-- Objects can vary tremendously in size and number. They can represent everything down to the hardware or all the way up to entire applications. How do we decide what should be an object?
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Identify the aspects of your application that vary and separate them from what stays the same.
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Program to an interface/supertype, not an implementation.
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Favor composition over inheritance.
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Strive for loosely coupled designs between objects that interact.
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Classes should be open for extension, but closed for modifi cation.
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Depend upon abstractions. Do not depend upon concrete classes.
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Principle of Least Knowledge - talk only to your immediate friends.
- Abstract Factory
- Provide an interface for creating families of related or dependent objects without specifying their concrete classes.
- 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.
- Bridge
- Decouple an abstraction from its implementation so that the two can vary independently.
- Builder
- Separate the construction of a complex object from its representation so that the same construction process can create different representations.
- 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.
- Command
- Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.
- Composite
- Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly.
- Decorator
- Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.
- Facade
- Provide a unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use.
- Factory Method
- Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.
- Flyweight
- Use sharing to support large numbers of fine-grained objects efficiently.
- Interpreter
- Given a language, define a represention for its grammar along with an interpreter that uses the representation to interpret sentences in the language.
- Iterator
- Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.
- 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.
- Memento
- Without violating encapsulation, capture and externalize an object's internal state so that the object can be restored to this state later.
- Observer
- Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
- Prototype
- Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype.
- Proxy
- Provide a surrogate or placeholder for another object to control access to it.
- Singleton
- Ensure a class only has one instance, and provide a global point of access to it.
- State
- Allow an object to alter its behavior when its internal state changes. The object will appear to change its class.
- Strategy
- Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.
- Template Method
- Define the 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 algorithm's structure.
- 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.
| Design Pattern | Aspect(s) that can vary |
|---|---|
| Abstract Factory | |
| Builder | how a composite object gets created |
| Factory Method | subclass of object that is instantiated |
| Prototype | class of object that is instantiated |
| Singleton | the sole instance of a class |
| Adapter | interface to an object |
| Bridge | implementation of an object |
| Composite | structure and composition of an object |
| Decorator | responsiblities of an object without subclassing |
| Facade | interface to a subsystem |
| Flyweight | storage cost of objects |
| Proxy | how an object is accessed; it's location |
| Chain of responsibility | object that can fulfill a request |
| Command | when and how a request is fulfilled |
| Interpreter | grammar and interpretation of a language |
| Iterator | how an aggreagate's element are accessed and traversed |
| Mediator | how and which objects interact with each other |
| Memento | what private information is stored outside an object, and when |
| Observer | number of objects that depend on another objects; how the dependant objects stay up to date |
| State | state of an object |
| Strategy | an algorithm |
| Template Method | steps of an algorithm |
| Visitor | operations that can be applied to objects without changing their classes |
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