Instance (computer science)

In object-oriented programming an instance is an occurrence or a copy of an object, whether currently executing or not. Instances of a class share the same set of attributes, yet will typically differ in what those attributes contain. For example, a class "Employee" would describe the attributes common to all instances of the Employee class. For the purposes of the task being solved Employee objects may be generally alike, but vary in such attributes as "name" and "salary". The description of the class would itemize such attributes and define the operations or actions relevant for the class, such as "increase salary" or "change telephone number." One could then talk about one instance of the Employee object with name = "Jane Doe" and another instance of the Employee object with name = "John Doe".

Class (computer programming): In object-oriented programming, a class is a construct that is used as a blueprint to create instances of itself – referred to as class instances, class objects, instance objects or simply objects. A class defines constituent members which enable these class instances to have state and behavior. Data field members (member variables or instance variables) enable a class object to maintain state. Other kinds of members, especially methods, enable a class object's behavior. Class instances are of the type of the associated class.

A class usually represents a noun, such as a person, place or (possibly quite abstract) thing, or something nominalized. For example, all fruits, bananas, apples and such would be instances of the class "Fruit" (a "Fruit" object). It is of the type "Fruit". This should not be confused with sub-types of. "Bananas" are a sub-type of "Fruit", but the class of "Bananas" itself is would not be an instance of "Fruit".