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abstract factory pattern, which provides an interface for creating related or dependent objects without specifying the objects' concrete classes. [3] builder pattern, which separates the construction of a complex object from its representation so that the same construction process can create different representations.
Encapsulate creating and assembling the parts of a complex object in a separate Builder object. A class delegates object creation to a Builder object instead of creating the objects directly. A class (the same construction process) can delegate to different Builder objects to create different representations of a complex object.
The object pool design pattern is used in several places in the standard classes of the .NET Framework. One example is the .NET Framework Data Provider for SQL Server. As SQL Server database connections can be slow to create, a pool of connections is maintained. Closing a connection does not actually relinquish the link to SQL Server.
In object oriented programming, objects provide a layer which can be used to separate internal from external code and implement abstraction and encapsulation. External code can only use an object by calling a specific instance method with a certain set of input parameters, reading an instance variable, or writing to an instance variable.
How can an object's instantiation be deferred to a subclass? Create an object by calling a factory method instead of directly calling a constructor. This enables the creation of subclasses that can change the way in which an object is created (for example, by redefining which class to instantiate).
Any object can be a service or a client; the names relate only to the role the objects play in an injection. The same object may even be both a client (it uses injected services) and a service (it is injected into other objects). Upon injection, the service is made part of the client's state, available for use. [12]
Design Patterns: Elements of Reusable Object-Oriented Software (1994) is a software engineering book describing software design patterns.The book was written by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides, with a foreword by Grady Booch.
Some languages take consideration of some special types of constructors. Constructors, which concretely use a single class to create objects and return a new instance of the class, are abstracted by factories, which also create objects but can do so in various ways, using multiple classes or different allocation schemes such as an object pool.