What is composition as it relates to object oriented design?

Question

What is Compositon? I understand inheritance from the point of Person : Mammal : Animal, but I can't really see the definition of Compostion anywhere.. Can somebody fill me in?

Answer 1

Composition is about building or composing an object (or type) from smaller or simpler ones.

Based on your own example say we have a person and mammal object as follows

Here we are building the Person object based on Mammal object, it is going to have all the properties of a mammal plus some specific complex characteristic.

Mammal:

List<Leg> 4Legs

List<Eye> 2Eyes

Person:

private Mammal _seipien

List<Calf> longCalf

String eyeColor