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#Design pattern samples in Java.
##Abstract Factory Intent: Provide an interface for creating families of related or dependent objects without specifying their concrete classes.
Applicability: Use the Abstract Factory pattern when
- a system should be independent of how its products are created, composed and represented
- a system should be configured with one of multiple families of products
- a family of related product objects is designed to be used together, and you need to enforce this constraint
- you want to provide a class library of products, and you want to reveal just their interfaces, not their implementations
##Builder Intent: Separate the construction of a complex object from its representation so that the same construction process can create different representations.
Applicability: Use the Builder pattern when
- the algorithm for creating a complex object should be independent of the parts that make up the object and how they're assembled
- the construction process must allow different representations for the object that's constructed
##Factory Method Intent: Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.
Applicability: Use the Factory Method pattern when
- a class can't anticipate the class of objects it must create
- a class wants its subclasses to specify the objects it creates
- classes delegate responsibility to one of several helper subclasses, and you want to localize the knowledge of which helper subclass is the delegate
##Prototype Intent: Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype.
Applicability: Use the Prototype pattern when a system should be independent of how its products are created, composed and represented; and
- when the classes to instantiate are specified at run-time, for example, by dynamic loading; or
- to avoid building a class hierarchy of factories that parallels the class hierarchy of products; or
- when instances of a class can have one of only a few different combinations of state. It may be more convenient to install a corresponding number of prototypes and clone them rather than instantiating the class manually, each time with the appropriate state
##Singleton Intent: Ensure a class only has one instance, and provide a global point of access to it.
##Adapter Intent: 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 Intent: Decouple an abstraction from its implementationso that the two can vary independently.
##Composite Intent: Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly.
##Decorator Intent: Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.
##Facade Intent: 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.
##Flyweight Intent: Use sharing to support large numbers of fine-grained objects efficiently.
##Proxy Intent: Provide a surrogate or placeholder for another object to control access to it.
##Chain of responsibility Intent: 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 Intent: Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.
##Interpreter Intent: Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language.
##Iterator Intent: Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.
##Mediator Intent: 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 Intent: Without violating encapsulation, capture and externalize an object's internal state so that the object can be restored to this state later.
##Observer Intent: Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
##State Intent: Allow an object to alter its behavior when its internal state changes. The object will appear to change its class.
##Strategy Intent: 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 Intent: 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 Intent: 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.