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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.
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.
They provide different ways to remove explicit references in the concrete classes from the code that needs to instantiate them. [8] In other words, they create independency for objects and classes. Consider applying creational patterns when: A system should be independent of how its objects and products are created.
A constructor is a method that is called at the beginning of an object's lifetime to create and initialize the object, a process called construction (or instantiation). Initialization may include an acquisition of resources. Constructors may have parameters but usually do not return values in most languages. See the following example in Java:
In object-oriented programming, a factory is an object for creating other objects; formally, it is a function or method that returns objects of a varying prototype or class [1] from some method call, which is assumed to be new. [a] More broadly, a subroutine that returns a new object may be referred to as a factory, as in factory method or ...
In many contexts, including C++, C# and Java, an object is created via special syntax like new typename(). In C++, that provides manual memory management, an object is destroyed via the delete keyword. In C# and Java, with no explicit destruction syntax, the garbage collector destroys unused objects automatically and non-deterministically.
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.
Primitive wrapper classes are not the same thing as primitive types. Whereas variables, for example, can be declared in Java as data types double, short, int, etc., the primitive wrapper classes create instantiated objects and methods that inherit but hide the primitive data types, not like variables that are assigned the data type values.