Provide an interface for creating families of related or dependent objects without specifying their concrete classes.
Builder
Separate the construction of a complex object from its representation so that the same construction process can create different representations.
List the collaborations involved with using "Builder"
- 1. Client creates a "Director" and a "Concrete Builder" instance (a "Builder" subclass for a particular representation), passing the latter to the former. - 2. Client tells the Director to construct the object. - 3. Director directs Builder to build an object (the "Product") by calling its methods. - 4. Client gets Product from Builder subclass instance.
Factory Method
Define an interface for creating an object, but let subclasses decide which class to instantiate. Lets a class defer instantiation to subclasses.
Prototype
Specify the kinds of objects to create using a prototypical instance and create new objects by copying this prototype.
Singleton
Ensure a class has only one instance and provide a global point of access to it.
Convert the interface of a class into another interface that clients expect. Lets classes work together that couldn't otherwise because of incompatible interface.
Bridge
Decouple an abstraction from its implementation so that the two can vary independently.
Composite
Compose objects into tree structures to represent part-whole hierarchies. Lets clients treat individual objects and compositions of objects uniformly.
Decorator
Attach flexible additional responsibilities to an object dynamically. They provide a flexible alternative to subclassing for extending functionality.
Facade
Provide a unified interface to a set of interfaces in a subsystem. Defines a higher-level interface that makes the subsystem easier to use.
Flyweight
Use sharing to support large numbers of fine-grained objects efficiently.
Proxy
Provide a surrogate or placeholder for another object to control access to it.
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 undo operations.
Interpreter
Given a language, define a representation for its grammar, along with a system that uses the representation to interpret sentences in the language.
Iterator
Provide a way to access the elements of an aggregate object sequentially with out exposing its underlying implementation.
Mediator
Define an object that encapsulates how a set of objects interact. Promotes loose coupling by keeping objects from referring to each other explicitly, and lets you vary their interaction independently.
Memento
Without violating encapsulation, capture and externalize an object's internal state so that objects can be restored to this state later.
Observer
Define a one-to-many dependency so that when one object changes state, all its dependents are notified and updated automatically.
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. Lets the algorithm vary independently from the clients that use it.
Template Method
Define the skeleton of an algorithm in an operation, deferring some steps to its subclasses. Lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.
Visitor
Represent an operation to be performed on elements of an object structure. Lets you define a new operation without changing the classes of the elements on which it operates.
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