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{{Short description|Software abstraction with state, behavior, and identity}}
In ], an '''object''' contains a combination of data and instructions, making it capable of receiving ], processing data, and sending messages to other objects. t role or responsibility.


In ], an '''object''' is an ] that has ], ], and ].<ref name="ooa">{{cite book|title=Object-Oriented Analysis and Design with Applications |edition=3 |date=April 30, 2007 |author1=Grady Booch |author2=Robert Maksimchuk |author3=Michael Engle |author4=Bobbi Young |author5=Jim Conallen |author6=Kelli Houston |isbn=020189551X |publisher= Addison-Wesley Professional}}</ref>{{rp|78}} An object can ] some part of ] or can be an ] of the ] whose collaborations with other such objects serve as the mechanisms that provide some higher-level behavior. Put another way, an object represents an individual, identifiable item, unit, or entity, either real or abstract, with a well-defined role in the problem domain.<ref name="ooa"></ref>{{rp|76}}
An object is an instance (or instantiation) of a ]. To use a particular class, an object of that class must first be created. To give a real world analogy, if a person who wanted to drive a car, neither a ] for a house, a photo of it, or a scale model would be of any use; what is needed is a real house constructed according to specifications.


A ] can be classified based on its support for objects. A language that provides an encapsulation construct for state, behavior, and identity is classified as ]. If the language also provides ] and ] it is classified as ]. A language that supports creating an object from a ] is classified as ]. A language that supports object creation via a template object is classified as ].
== Theory ==


The concept of object is used in many different software contexts, including:
In strictly ] branches of ] the term '''object''' is used in a purely mathematical sense to refer to any "thing". While this interpretation is useful in the discussion of abstract theory, it is not concrete enough to serve as a ] ] in the discussion of more concrete branches (such as ]) that are closer to actual computation and ]. Therefore, objects are still '''conceptual entities''', but generally correspond directly to a contiguous block of ] of a specific size at a specific location. This is because computation and information processing ultimately require a form of computer memory. Objects in this sense are fundamental primitives needed to accurately define concepts such as ]s, ]s, and ]. This is why the rest of this article will focus on the concrete interpretation of ''object'' rather than the abstract one &ndash; object oriented programming.


* Possibly the most common use is ] objects in a ] written in an object-based language.
Note that although a block of computer memory can appear contiguous on one level of ] and incontiguous on another, the important thing is that it appears contiguous to the program that treats it as an object. That is, an object's private implementation details must not be exposed to clients of the object, and they must be able to change without requiring changes to client code.


* ] can be ] with objects representing their components and interfaces.<ref name="ooa"/>{{rp|39}}
Objects exist only within contexts that are aware of them; a piece of computer memory only holds an object if a program treats it as such (for example by reserving it for exclusive use by specific procedures and/or associating a ] with it). Thus, the ] is the time during which it is treated as an object. This is why they are still conceptual entities, despite their physical presence in computer memory.
* In the ] of ] management, aspects such as ] and ] may act as objects.<ref name=Oppel>{{cite book |first=Andy |last=Oppel |title=SQL Demystified |publisher=McGraw Hill |year=2005| page=7 |isbn=0-07-226224-9}}</ref>


* ] of a ] system tend to be larger grained, longer lasting, and more service-oriented than programming objects.
In other words, abstract concepts that do not occupy memory space at runtime are, according to the definition, not objects; e.g., ] exhibited by a set of classes, ]s in statically typed programs.


⚫ ==See also==
== Objects in object-oriented programming ==
*{{annotated link|Actor model}}
*{{annotated link|Business object}}
⚫ *{{annotated link|Object lifetime}}
*{{annotated link|Object copying}}
*{{annotated link|Semantic Web}}


==References==
In ] (OOP), an instance of a program (i.e. a program running in a computer) is treated as a dynamic set of interacting objects. Objects in OOP extend the more general notion of objects described above to include a very specific kind of ], which among other things allows for:
{{Reflist}}
# data members that represent the data associated with the object.
# ]s that access the data members in predefined ways.
In the case of most objects, the data members can only be accessed through the methods, making it easy to guarantee that the data will always remain in a well-defined state (]s will be enforced). Some languages do not make distinctions between data members and methods.

In almost all object-oriented programming languages, a dot(.) operator is used to call a particular method/function of an object. For example, consider an arithmetic class named Arith_Class. This class contains functions like add(), subtract(), multiply() and divide(), that process results for two numbers sent to them. This class could be used to find the product of 78 and 69 by first of all creating an object of the class and then invoking its multiply method, as follows:

1 int result = 0; ''// Initialization''
2 arith_Obj1 = new Arith_Class(); ''// Creating a new instance of Arith_Class''
3 result = arith_Obj1.multiply(78,69); ''// Product of 78 and 69 stored in result variable

In a language where each object is created from a class, an object is called an '''instance''' of that class. If each object has a type, two objects with the same class would have the same ]. Creating an instance of a class is sometimes referred to as '''instantiating''' the class.

A real-world example of an object would be "my dog", which is an instance of a ] (a ]) called "dog", which is a ] of a class "animal". In the case of a ] object, some details of its type can be selectively ignored, for example a "dog" object could be used by a function looking for an "animal". So could a "cat", because it too belongs to the class of "animal". While being accessed as an "animal", some member attributes of a "dog" or "cat" would remain unavailable, such as the "tail" attribute, because not all animals have tails.

A ghost is an object that is ] in a ], and can therefore serve no purpose. In a garbage-collected language, the ] would mark the memory occupied by the object as free, although it would still contain the object's data until it was overwritten.

Three properties characterize objects:
# ]: the property of an object that distinguishes it from other objects
# State: describes the data stored in the object
# Behavior: describes the methods in the object's ] by which the object can be used

Some terms for specialized kinds of objects include:
*] object: An object that is the only instance of its class during the lifetime of the program.
*Functor (]): an object with a single method (in C++, this method would be the function operator, "operator()") that acts much like a function (like a C/C++ pointer to a function).
*]: an object set up with a fixed state at creation time and which does not vary afterward.
*]: an object that can be used without restriction.
*]: an object that can contain other objects.
*]: an object whose purpose is to create other objects.
*]: an object from which other objects can be created (Compare with ], which is not necessarily an object)
*]: a specialized metaobject from which other objects can be created by copying
*]: an object that knows ''too much'' or does ''too much''. The God object is an example of an ].
*]: a computational metaphor useful to conceptualize and solve hard problems often with massively parallel approaches by swapping computational foreground and background.

⚫ == See also ==
⚫ *]
*]
⚫ *]
*]
*]


==External links== ==External links==
* from ''The Java Tutorials'' * from ''The Java Tutorials''


{{Software engineering}}
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Latest revision as of 13:40, 31 October 2024

Software abstraction with state, behavior, and identity

In software development, an object is an entity that has state, behavior, and identity. An object can model some part of reality or can be an invention of the design process whose collaborations with other such objects serve as the mechanisms that provide some higher-level behavior. Put another way, an object represents an individual, identifiable item, unit, or entity, either real or abstract, with a well-defined role in the problem domain.

A programming language can be classified based on its support for objects. A language that provides an encapsulation construct for state, behavior, and identity is classified as object-based. If the language also provides polymorphism and inheritance it is classified as object-oriented. A language that supports creating an object from a class is classified as class-based. A language that supports object creation via a template object is classified as prototype-based.

The concept of object is used in many different software contexts, including:

See also

  • Actor model – Model of concurrent computation
  • Business object – Entity within a multi-tiered software application
  • Object lifetime – Time period between the creation and destruction of an object-oriented programming instance
  • Object copying – Technique in object-oriented programming
  • Semantic Web – Extension of the Web to facilitate data exchange

References

  1. ^ Grady Booch; Robert Maksimchuk; Michael Engle; Bobbi Young; Jim Conallen; Kelli Houston (April 30, 2007). Object-Oriented Analysis and Design with Applications (3 ed.). Addison-Wesley Professional. ISBN 020189551X.
  2. Oppel, Andy (2005). SQL Demystified. McGraw Hill. p. 7. ISBN 0-07-226224-9.

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