The object-oriented paradigm was first conceived in the 1960's and implemented in languages such as SIMULA-67. One of the initial concerns with early object-oriented languages was their efficiency. Programs written using structured languages, such as Pascal and C, executed faster than programs written using early object-oriented languages. Although programs which used the object-oriented paradigm were more extensible and easier to maintain from a programmer's point of view, an unacceptable price had to be paid in the program's runtime behaviour. Recently, however, the runtime execution of object-oriented programs has improved considerably. This has been due in part to both the development of faster hardware and the creation of efficient languages and compilers which support object-oriented programming, such as C++. These facts, in addition to the ever-increasing accessibility of object-oriented languages to the common programmer has created a major evolution in the area of software development.
There is, as yet, no universally agreed upon definition of exactly what constitutes object-oriented programming. Booch [1] suggests:
``Object-oriented programming is a method of implementation in which programs are organized as cooperative collections of objects, each of which represents an instance of some class, and whose classes are all members of a hierarchy of classes united via inheritance relationships.''
From this definition, one can infer that object-oriented programming consists of instantiating a number of objects which communicate with one another so as to achieve some desired behaviour. This paradigm is natural with how humans see the world; as a series of cause-effect relationships, where an action performed on one object has effects on the objects with which it communicates.