In object-oriented programming with classes, a class variable is a variable defined in a class (i.e. a member variable) of which a single copy exists, regardless of how many instances of the class exist.
A class variable is the opposite of an instance variable. It is a special type of class attribute (or class property, field, or data member).
In Java, C#, and C++, class variables are declared with the keyword
static, and may therefore be referred to as static member variables.
The same dichotomy between instance and class members applies to methods ("member functions") as well; a class may have both instance methods and class methods. Again, Java, C#, and C++ use the keyword
static to indicate that a method is a class method ("static member function").
In this C++ example, the class variable
Request::count is incremented on each call to the constructor, so that
Request::count always holds the number of Requests that have been constructed, and each new Request object is given a
number in sequential order. Since
count is a class variable, there is only one object
Request::count; in contrast, each Request object contains its own distinct
ca:Variable de classe es:Variable de clase ja: ta: