OOP: When is it an object?

Question

I\'m trying to understand object orientation. I understand it a little bit of course, but sometimes I\'m not 100% clear. How do you decide what should be turned into an object (

Answer 1

It is an object if you need to think about it as... an object.

That is, if you need an abstraction.

The "key hole" in your example can be described on different levels of abstraction and only the last one from the list you would probably call "an object":

1) Could be a boolean property, if you just need to know that your door has it:

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class Door
{
    bool HasKeyHole;
}

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2) Could be a pair of coordinates, if you just want to draw your door and put a circle in place of the key hole

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 class Door
 {
    Point KeyHoleCoordinates;
 }

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3) Could be a specially defined class KeyHole if you want to encapsulate logic and some properties of a key hole and work with them together, probably passing them around, or allowing interaction with a Key

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class KeyHole
{
    Point Coordinates;
    bool OpensWithKey(Key key);
}

class Door
{
    KeyHole Hole;
}

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