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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.
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.
According to Design Patterns: Elements of Reusable Object-Oriented Software: "Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory method lets a class defer instantiation to subclasses." [2] Creating an object often requires complex processes not appropriate to include within a composing object.
The way to create objects varies across programming contexts. In some class-based languages, a constructor handles initialization. Like other methods, a constructor can be overloaded in order to support creating with different initial state.
In class-based programming, a factory is an abstraction of a constructor of a class, while in prototype-based programming a factory is an abstraction of a prototype object. A constructor is concrete in that it creates objects as instances of one class, and by a specified process (class instantiation), while a factory can create objects by instantiating various classes, or by using other ...
The messages that flow between computers to request services in a client-server environment can be designed as the linearizations of objects defined by class objects known to both the client and the server. For example, a simple linearized object would consist of a length field, a code point identifying the class, and a data value.
A disadvantage is that one often cannot access the clone() method on an abstract type. Most interfaces and abstract classes in Java do not specify a public clone() method. Thus, often the only way to use the clone() method is if the class of an object is known, which is contrary to the abstraction principle of using the most generic type possible.