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[KBleivik]

Object oriented programming is about, data abstraction (you can make your own data types) structure and reuse (inheritance) evolution and correctness.

The following very important quotation, makes me draw the conclusion that SIMULA was the first object oriented language:

"SIMULA I (1962-65) and Simula 67 (1967) are the two first object-oriented languages. Simula 67 introduced most of the key concepts of object-oriented programming: both objects and classes, subclasses (usually referred to as inheritance) and virtual procedures, combined with safe referencing and mechanisms for bringing into a program collections of program structures described under a common class heading (prefixed blocks)".

Read more ...

On that page you can also see the following short note:

"When was object-orientation first used?"

In my opinion this discussion is rather silly, since you had to think about and organise your computation in a way that later could be described as "object-oriented" if your task at hand so demanded. I could argue that my Monte Carlo-calculations in 1949 (to determine the proper radius of the uranium rods of the first civilian reactor in Europe) were an example of object-orientation, even if the calculations were carried out by a group of people using electromechanical desk calculators. In the same manner, all earlier and later simulation (and some engineering) schemes may in retrospect be characterised as "object-oriented", You will find in the early litterature that some people maintained that Algol and even Fortran were excellent simulation languages.

However, object-orientation did not come into existencs till 1965 as an articulated way of system description and programming, built upon precise, general concepts materialised as concise language constructs, allowing a common approach to understanding wide classes of phenomena. To use an analogy, gravitation for sure existed before Newton. and people certainly had to take that into account in their designs. Few will describe these designs as being "early approaches to the theory of gravitation"

My private conclusion:

• Newton developed and formalized the theory of gravitation.
  
• Ole-Johan Dahl and Kristen Nygaard developed and formalized the first object oriented program, SIMULA.
  

Literature:

Bjørn Kirkerud (1989): "Object Oriented Programming With Simula". Addison Wesley Publishing Company ISBN 0 201 17574 6
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Kjell Gunnar Bleivik
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