Object-oriented programming is a programming paradigm using "objects": data structures consisting of data fields and methods together with their interactions.

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The goal behind ISP is that no client consuming an interface should be forced to depend on methods it does not use.


In this article we'll look at how the Single Responsibility Principle is subjective, but also how the principle is still helpful in the code.


Subtypes and supertypes are a common part of modern programming. Covariance and contravariance tell us where subtypes are accepted and where supertypes are accepted in place of the original type.


The most important concept in software engineering is the concept of an interface. This article is not about interfaces in Java, it is about interfaces in software design, and to a lesser extent, interfaces anywhere in the universe. There are many other important concepts used in software development, but I would argue that many of them actually end up relating back to why interfaces are so important.


The idea of sharing code this way dates back to 1967, specifically to the SIMULA language which is credited to have been responsible for the birth of object oriented programming.