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Object Orientation
The first object-oriented application was implemented in Simula 67, which was the first object-oriented programming language. Object-oriented modelling takes the following view: The (modelled) world consists of a set of objects that represents self-contained units. They know their own micro world where their states are stored in fields and their possible behaviour patterns in methods. Objects can communicate with the outside world, i.e., with other objects, by sending and receiving messages. These objects are classified so that all objects of the same kind belong to one class (i.e., they have the same type). To access such an object, we must send it a message, which can contain parameters. In object orientation, the procedure that processes a given message is called a method and is invisible to the outside, just as the object’s data is hidden. The answer is returned in the form of a message. This is the only way to access an object. The messages and their parameters are specified in advance. Object-oriented programming In object-oriented programming objects consist of a set of object fields (also called instance variables) which define the state space of the object, and methods which describe the behaviour of the object. Objects have a type, and individual objects are instances of this type. Objects are classified according to their class membership. Many languages have an absolute root class to which all objects belong per definition. What is a class? A class is an abstract data type equipped with a possibly partial implementation. A class which is fully implemented is said to be effective. A class which is implemented only partially, or not at all, is said to be deferred. What is an object? An object is simply a run-time instance of some class. The definition of “class” yields as a by-product a definition of “object”. The software texts that serve to produce systems are classes. Objects are a run-time notion only: they are created and manipulated by the software during its execution. PDF - Document: Object-Oriented programming [Sources: Bertrand Meyer; Object-Oriented Software Construction (Second Edition), 1997,Laszlo Böszörmenyi, Carsten Weich; Programming in Modula-3; 1996]
 

 

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