object-oriented programming
[¦äb‚jekt ‚ȯr·ē‚en·təd ′prō‚gram·iŋ]Object-oriented programming
A computer-programming methodology that focuses on data items rather than processes. Traditional software development models assume a top-down approach. A functional description of a system is produced and then refined until a running implementation is achieved. Data structures (and file structures) are proposed and evaluated based on how well they support the functional models.
The object-oriented approach focuses first on the data items (entities, objects) that are being manipulated. The emphasis is on characterizing the data items as active entities which can perform operations on and for themselves. It then describes how system behavior is implemented through the interaction of the data items.
The essence of the object-oriented approach is the use of abstract data types, polymorphism, and reuse through inheritance.
Abstract data types define the active data items described above. A traditional data type in a programming language describes only the structure of a data item. An abstract data type also describes operations that may be requested of the data item. It is the ability to associate operations with data items that makes them active. The abstract data type makes operations available without revealing the details of how the operations are implemented, preventing programmers from becoming dependent on implementation details. The definition of an operation is considered a contract between the implementor of the abstract data type and the user of the abstract data type. The implementor is free to perform the operation in any appropriate manner as long as the operation fulfills its contract. Object-oriented programming languages give abstract data types the name class.
Polymorphism in the object-oriented approach refers to the ability of a programmer to treat many different types of objects in a uniform manner by invoking the same operation on each object. Because the objects are instances of abstract data types, they may implement the operation differently as long as they fulfill the agreement in their common contract.
A new abstract data type (class) can be created in object-oriented programming simply by stating how the new type differs from some existing type. A feature that is not described as different will be shared by the two types, constituting reuse through inheritance. Inheritance is useful because it replaces the practice of copying an entire abstract data type in order to change a single feature.
In the object-oriented approach, a class is used to define an abstract data type, and the operations of the type are referred to as methods. An instance of a class is termed an object instance or simply an object. To invoke an operation on an object instance, the programmer sends a message to the object.
object-oriented programming
(programming)Each class is a separate module and has a position in a "class hierarchy". Methods or code in one class can be passed down the hierarchy to a subclass or inherited from a superclass. This is called "inheritance".
A procedure call is described as invoking a method on an object (which effectively becomes the procedure's first argument), and may optionally include other arguments. The method name is looked up in the object's class to find out how to perform that operation on the given object. If the method is not defined for the object's class, it is looked for in its superclass and so on up the class hierarchy until it is found or there is no higher superclass.
OOP started with SIMULA-67 around 1970 and became all-pervasive with the advent of C++, and later Java. Another popular object-oriented programming language (OOPL) is Smalltalk, a seminal example from Xerox's Palo Alto Research Center (PARC). Others include Ada, Object Pascal, Objective C, DRAGOON, BETA, Emerald, POOL, Eiffel, Self, Oblog, ESP, Loops, POLKA, and Python. Other languages, such as Perl and VB, permit, but do not enforce OOP.
FAQ. http://zgdv.igd.fhg.de/papers/se/oop/. http://cuiwww.unige.ch/Chloe/OOinfo.
Usenet newsgroup: news:comp.object.
object-oriented programming
A programming language structure wherein the data and their associated processing ("methods") are defined as self-contained entities called "objects." The norm today, object-oriented programming (OOP) languages, such as C++ and Java, provide a formal set of rules for creating and managing objects. The data are stored in a traditional relational database or in an object database if the data have a complex structure. See O-R mapping and object database.There are three major features in object-oriented programming that makes them different than non-OOP languages: encapsulation, inheritance and polymorphism.
Encapsulation Enforces Modularity
Encapsulation refers to the creation of self-contained modules that bind processing functions to the data. These user-defined data types are called "classes," and one instance of a class is an "object." For example, in a payroll system, a class could be Manager, and Pat and Jan could be two instances (two objects) of the Manager class. Encapsulation ensures good code modularity, which keeps routines separate and less prone to conflict with each other.
Inheritance Passes "Knowledge" Down
Classes are created in hierarchies, and inheritance allows the structure and methods in one class to be passed down the hierarchy. That means less programming is required when adding functions to complex systems. If a step is added at the bottom of a hierarchy, only the processing and data associated with that unique step needs to be added. Everything else is inherited. The ability to reuse existing objects is considered a major advantage of object technology.
Polymorphism Takes any Shape
Object-oriented programming allows procedures about objects to be created whose exact type is not known until runtime. For example, a screen cursor may change its shape from an arrow to a line depending on the program mode. The routine to move the cursor on screen in response to mouse movement would be written for "cursor," and polymorphism allows that cursor to take on whatever shape is required at runtime. It also allows new shapes to be easily integrated.
OOP Languages
Used for simulating system behavior in the late 1960s, SIMULA was the first object-oriented language. In the 1970s, Xerox's Smalltalk was the first object-oriented programming language, which was used to create the graphical user interface (see Xerox Star). ACTOR and Eiffel were also earlier OOP languages.
Today, C++, C#, Java, JavaScript, Visual Basic.NET and Python are popular object-oriented languages. The following compares basic OOP terms with traditional programming. See object-oriented DBMS.
OOP Traditional Programming class define data + processing object data + processing attribute data (a field) method function message function call instantiate allocate a structure
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| Relational vs. Object Modeling |
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| Instead of separate employee, department and job tables, an employee class contains the data and processing for all employees. Each subclass (manager, secretary, etc.) has its own data and processing but also inherits everything from the employee class. Changes made to the employee class affect every subclass. |