In a computer system, any time a new context is created based on some model, it is said that the model has been instantiated. In practice, this instance usually has a data structure in common with other instances, but the values stored in the instances are separate. Changing the values in one instance will then not interfere with the values of some other instance. A compute instance can be software or hardware which can run code, for example a

CPU A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, a ...

GPU A graphics processing unit (GPU) is a specialized electronic circuit designed to manipulate and alter memory to accelerate the creation of images in a frame buffer intended for output to a display device. GPUs are used in embedded systems, mobi ...

or a

virtual machine In computing, a virtual machine (VM) is the virtualization/ emulation of a computer system. Virtual machines are based on computer architectures and provide functionality of a physical computer. Their implementations may involve specialized h ...

Computer graphics

In computer graphics, a polygonal model can be instantiated in order to be drawn several times in different locations in a scene. This is a technique that can be used to improve the performance of rendering, since the work needed to display each instance overlaps.

Object-oriented programming

object-oriented programming Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of ...

(OOP), an instance is a concrete occurrence of any

object Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** Object (abstract), an object which does not exist at any particular time or place ** Physical object, an identifiable collection of matter * Goal, an ...

, existing usually during the runtime of a computer program. Formally, "instance" is synonymous with "object" as they are each a particular value (realization), and these may be called an instance object; "instance" emphasizes the distinct identity of the object. The creation of an instance is called instantiation. An object may be varied in a number of ways. Each realized variation of that object is an instance of its class. That is, it is a member of a given class that has specified

values In ethics and social sciences, value denotes the degree of importance of something or action, with the aim of determining which actions are best to do or what way is best to live (normative ethics in ethics), or to describe the significance of di ...

rather than variables. In a non-programming context, you could think of "dog" as a type and your particular dog as an instance of that class. In

class-based programming Class-based programming, or more commonly class-orientation, is a style of object-oriented programming (OOP) in which inheritance occurs via defining ''classes'' of objects, instead of inheritance occurring via the objects alone (compare prototy ...

, objects are created from classes by

subroutine In computer programming, a function or subroutine is a sequence of program instructions that performs a specific task, packaged as a unit. This unit can then be used in programs wherever that particular task should be performed. Functions may ...

s called constructors, and destroyed by destructors. An object is an instance of a class, and may be called a class instance or class object; instantiation is then also known as construction. Not all classes can be instantiated

abstract class In programming languages, an abstract type is a type in a nominative type system that cannot be instantiated directly; a type that is not abstract – which ''can'' be instantiated – is called a ''concrete type''. Every instance of an abstra ...

es cannot be instantiated, while classes that can be instantiated are called

concrete class In object-oriented programming, a class is an extensible program-code-template for creating objects, providing initial values for state ( member variables) and implementations of behavior (member functions or methods). In many languages, the clas ...

es. In

prototype-based programming Prototype-based programming is a style of object-oriented programming in which behaviour reuse (known as inheritance) is performed via a process of reusing existing objects that serve as prototypes. This model can also be known as ''prototypal ...

, instantiation is instead done by copying (cloning) a prototype instance.

Operating systems

In the context of POSIX-oriented operating systems, the term "(program) instance" typically refers to any executing process instantiated from that program (via

system calls In computing, a system call (commonly abbreviated to syscall) is the programmatic way in which a computer program requests a service from the operating system on which it is executed. This may include hardware-related services (for example, a ...

, e.g. fork() and exec()); that is, each executing process in the OS is an instance of some program which it has been instantiated from.

References

{{Reflist __notoc__ Object (computer science)