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Let's start with a quick introduction to object orientation and

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the fundamental concepts behind it. And let's start by discussing what

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exactly is object orientation? If you're younger than me, it

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could be that the first programming language you learned was already

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an object-oriented language. But things were not always like this.

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Before object orientation became prevalent, people were not used to thinking

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in terms of objects. So what happened afterwards? And what does

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it mean to think in terms of objects and to follow

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an object-oriented approach? First of all, it

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means to give precedence of data over function.

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Did items rather than functionality become the center

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of development activities. This also allows for enforcing

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the very important concept of information hiding,

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which is the encapsulation and segregation of data

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behind well-defined and ideally stable interfaces. In order

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to be able to hide the design and

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also implementation decisions. And note that the terms

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encapsulation and information hiding are often used interchangeably, although

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some people prefer to think of information hiding

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as being the principle and encapsulation being the technique

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to achieve information hiding. The key concept though,

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no matter which term you use, is really to

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gather, to seclude this data behind sort of

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a wall and give access to the data only

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through interfaces that you, the developer define. And why is

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that important? Oh, for many reasons, and one of the main

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ones is that it makes code more maintainable. Because the

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rest of the code, the rest of the system doesn't have

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to be concerned on how the implementation details or the

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design are defined. And therefore, any change that happens behind this

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wall doesn't concern the rest of the system. And, doesn't

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affect the rest of the system, as long as you keep

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your interfaces consistent. Another advantage of focusing on

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objects and encapsulating the information into cohesive entities is

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that it allows the reuse of object definitions

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by incremental refinement. Which is what we normally call

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inheritance. And inheritance is definitely a fundamental concept

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in object orientation. For example, we can define a

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car as a refinement of the vehicle. That there's

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some additional characteristics with respect to a generic vehicle.

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And then we can use the car wherever a vehicle can be used, which is what we

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call polymorphism. And we'll continue this discussion for a

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very long time. Because there's so many things that

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could be discussed when we talk about object orientation,

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its characteristics and its advantages. But in the interest

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of time, let's for now just stop here. And

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start talking about two key concepts in object orientation.