object-oriented programming

object-oriented programming, a modular approach to computer program (software) design. Each module, or object, combines data and procedures (sequences of instructions) that act on the data; in traditional, or procedural, programming the data are separated from the instructions. A group of objects that have properties, operations, and behaviors in common is called a class. By reusing classes developed for previous applications, new applications can be developed faster with improved reliability and consistency of design. The first object-oriented programs, written in the language Simula 67, were used extensively for modeling and simulation, primarily in Europe during the late 1960s and early 1970s. The technique was popularized in the United States during the following decade using the language SmallTalk and achieved its greatest prominence with the development of the object-oriented language C++ during the late 1980s and 1990s.

Bibliography

See P. W. Oman and T. G. Lewis, Milestones in Software Evolution (1990); T. Budd, An Introduction to Object-Oriented Programming (1991); P. Varhol, Object-Oriented Programming: The Software Development Revolution (1993); P. Coad and J. Nicola, OOP, Object-Oriented Programming (1993).

---

object-oriented programming (OOP)

Computer programming that emphasizes the structure of data and their encapsulation with the procedures that operate upon it. It is a departure from traditional or procedural programming. OOP languages incorporate objects that are self-contained collections of computational procedures and data structures. Programs can be written by assembling sets of these predefined objects in far less time than is possible using conventional procedural languages. OOP has become extremely popular because of its high programming productivity. C++ and Objective-C (early 1980s) are object-oriented versions of C that have gained much popularity. See also Java.

---

Writing software that supports a model wherein the data and their associated processing (called "methods") are defined as self-contained entities called "objects." Object-oriented programming (OOP) languages, such as C++ and Java, provide a formal set of rules for creating and managing objects. The data in an object model can be stored in the traditional table structure of a relational database (see O-R mapping) or, if the object model is very complex, in an object database, which is designed to hold object data (see object database).

Encapsulation, Inheritance and Polymorphism
There are three major features in object-oriented programming: 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, then only the processing and data associated with that unique step needs to be added. Everything else about that step 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 and was used to create the graphical user interface (GUI). Today, C++ and Java are the major OOP languages, while C#, Visual Basic.NET, Python and JavaScript are also popular. ACTOR and Eiffel were earlier OOP languages. The following list compares some basic OOP terms with traditional programming. See object technology and object-oriented DBMS.

   OOP                 Traditional Programming

   class               description of data +
                         processing

   object (instance)   actual data + processing

   attribute           actual data (a field)

   method              function that processes a
                         particular structure

   message             function call

   instantiate         allocate a structure

Object Modeling

When information systems are modeled as objects, they can employ the powerful inheritance capability. Instead of building a table of employees with department and job information in separate tables, the type of employee is modeled. The employee class contains the data and the processing for all employees. Each subclass (manager, secretary, etc.) contains the data and processing unique to that person's job. Changes can be made globally or individually by modifying the class in question.

---

(programming)

object-oriented programming - (OOP) The use of a class of programming languages and techniques based on the concept of an "object" which is a data structure (abstract data type) encapsulated with a set of routines, called "methods", which operate on the data. Operations on the data can __only__ be performed via these methods, which are common to all objects that are instances of a particular "class". Thus the interface to objects is well defined, and allows the code implementing the methods to be changed so long as the interface remains the same. 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.