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In object-oriented programming, a class defines the shared aspects of objects created from the class. The capabilities of a class differ between programming languages , but generally the shared aspects consist of state ( variables ) and behavior ( methods ) that are each either associated with a particular object or with all objects of that class.
Class variables – belong to the class itself, so all objects in the class share one copy. Instance variables – belong to individual objects; every object has its own version of these variables. Member variables – refers to both the class and instance variables that are defined by a particular class.
This is analogous to class declarations as used in other object-oriented languages, such as C++ or Python. The interface of a class is usually defined in a header file. A common convention is to name the header file after the name of the class, e.g. Ball.h would contain the interface for the class Ball. An interface declaration takes the form:
Guido van Rossum began working on Python in the late 1980s as a successor to the ABC programming language and first released it in 1991 as Python 0.9.0. [36] Python 2.0 was released in 2000. Python 3.0, released in 2008, was a major revision not completely backward-compatible with earlier versions. Python 2.7.18, released in 2020, was the last ...
Cocoa is Apple's native object-oriented application programming interface (API) for its desktop operating system macOS.. Cocoa consists of the Foundation Kit, Application Kit, and Core Data frameworks, as included by the Cocoa.h header file, and the libraries and frameworks included by those, such as the C standard library and the Objective-C runtime.
Python allows the creation of class methods and static methods via the use of the @classmethod and @staticmethod decorators. The first argument to a class method is the class object instead of the self-reference to the instance. A static method has no special first argument. Neither the instance, nor the class object is passed to a static method.
In Objective-C, for example, both the generic Object and NSObject (in Cocoa/OpenStep) provide the method isMemberOfClass: which returns true if the argument to the method is an instance of the specified class.
When a member function is called on an object, it invokes the member function with the same name on the object's class object, with the object automatically bound to the first argument of the function. Thus, the obligatory first parameter of instance methods serves as this; this parameter is conventionally named self, but can be named anything.