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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 ...
In object-oriented programming, the factory method pattern is a design pattern that uses factory methods to deal with the problem of creating objects without having to specify their exact classes. Rather than by calling a constructor , this is accomplished by invoking a factory method to create an object.
For example, if one has a List reference in Java, one cannot invoke clone() on that reference because List specifies no public clone() method. Implementations of List like Array List and Linked List all generally have clone() methods, but it is inconvenient and bad abstraction to carry around the class type of an object.
Java enables classes to be defined inside methods. These are called local classes. When such classes are not named, they are known as anonymous classes (or anonymous inner classes). A local class (either named or anonymous) may refer to names in lexically enclosing classes, or read-only variables (marked as final) in the lexically enclosing method.
Prototype also provides library functions to support classes and class-based objects. [2] In JavaScript, object creation is prototype-based instead: an object creating function can have a prototype property, and any object assigned to that property will be used as a prototype for the objects created with that function. The Prototype framework ...
Using a factory method to create instances of a class (factory method pattern) Storing the instances in a map, and returning the same instance to each request for an instance with same parameters (multiton pattern) Using lazy initialization to instantiate the object the first time it is requested (lazy initialization pattern)
The object methods include access to the object state (via an implicit or explicit parameter that references the object) whereas class methods do not. If the language supports inheritance , a class can be defined based on another class with all of its state and behavior plus additional state and behavior that further specializes the class.
There are methods that a subclass cannot override. For example, in Java, a method that is declared final in the super class cannot be overridden. Methods that are declared private or static cannot be overridden either because they are implicitly final. It is also impossible for a class that is declared final to become a super class. [9]