Design Patterns

I expect to present code for a variety of design patterns, for my own edification, many of I which already use in production applications.

The original source:  http://en.wikipedia.org/wiki/Design_Patterns 

Below is a list compiled from other sources, unattributed:

Pattern Type	Name	Description
Creational	Abstract factory	Provide an interface for creating families of related or dependent objects without specifying their concrete classes.
	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.
	Builder	Separate the construction of a complex object from its representation so that the same construction process can create different representations.
	Lazy initialization	Tactic of delaying the creation of an object, the calculation of a value, or some other expensive process until the first time it is needed.
	Object pool	Avoid expensive acquisition and release of resources by recycling objects that are no longer in use
	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.
	Multiton	Ensure a class has only named instances, and provide global point of access to them.
	Resource acquisition is initialization	Ensure that resources are properly released by tying them to the lifespan of suitable objects.
Structural	Adapter or Wrapper	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.
	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 keeping the same interface. 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.
	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.
Behavioral	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.
	Interpreter	Given a language, define a representation 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.
	Restorer	An alternative to the existing Memento pattern.
	Memento	Without violating encapsulation, capture and externalize an object's internal state so that the object can be restored to this state later.
	Null Object	designed to act as a default value of an object.
	Observer or Publish/subscribe	Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
	Blackboard	Generalized observer, which allows multiple readers and writers. Communicates information system-wide.
	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.
	Specification	Recombinable business logic in a boolean fashion
	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.
Concurrency	Active Object	The Active Object design pattern decouples method execution from method invocation that reside in their own thread of control. The goal is to introduce concurrency, by using asynchronous method invocation and a scheduler for handling requests.
	Binding Properties	Combining multiple observers to force properties in different objects to be synchronized or coordinated in some way.[14]
	Event-Based Asynchronous	The event-based asynchronous design pattern addresses problems with the Asynchronous Pattern that occur in multithreaded programs.[15]
	Balking	The Balking pattern is a software design pattern that only executes an action on an object when the object is in a particular state.
	Guarded suspension	In concurrent programming, guarded suspension is a software design pattern for managing operations that require both a lock to be acquired and a precondition to be satisfied before the operation can be executed.
	Monitor object	A monitor is an approach to synchronize two or more computer tasks that use a shared resource, usually a hardware device or a set of variables.
	Scheduler	The scheduler pattern is a concurrency pattern used to explicitly control when threads may execute single-threaded code.
	Thread pool	In the thread pool pattern in programming, a number of threads are created to perform a number of tasks, which are usually organized in a queue. Typically, there are many more tasks than threads.
	Thread-specific storage	Thread-local storage (TLS) is a computer programming method that uses static or global memory local to a thread.
	Reactor	The reactor design pattern is a concurrent programming pattern for handling service requests delivered concurrently to a service handler by one or more inputs. The service handler then demultiplexes the incoming requests and dispatches them synchronously to the associated request handlers.
	Lock	One thread puts a "lock" on a resource, preventing other threads from accessing or modifying it.[16]
	Double checked locking	Double-checked locking is a software design pattern also known as "double-checked locking optimization". The pattern is designed to reduce the overhead of acquiring a lock by first testing the locking criterion (the 'lock hint') in an unsafe manner; only if that succeeds does the actual lock proceed.
		The pattern, when implemented in some language/hardware combinations, can be unsafe. It can therefore sometimes be considered an anti-pattern.
	Read write lock	Allows concurrent read access to an object but requires exclusive access for write operations.http://en.wikipedia.org/wiki/Design_Patternshttp://en.wikipedia.org/wiki/Design_Patterns