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) A programming technique that combines data abstraction, inheritance, and dynamic type binding. The central feature is the object, which comprises a data structure definition and its defined procedures in a single structure. Objects are instances of a class, each instance having its own private instance variables. The class definition defines the properties of the objects in a class. Hierarchical class structures are possible in which objects in a class inherit the properties of the parent class in addition to properties explicitly defined for the class. This facilitates sharing of code, since users can inherit objects from system collections of code.

The procedures of an object (often called methods) are activated by messages sent to the object by another object. Thus in an object-oriented programming system the basic control structure is message passing. The programmer identifies the real-world objects of the problem and the processing requirements of those objects, encapsulating these in class definitions, and the communications between objects. The program is then essentially a simulation of the real world in which objects pass messages to other objects to initiate actions.

The most complete realization of an object-oriented programming system is Smalltalk; the concepts also appear in combination with conventional languages, for example C++ and CLOS.