Tài liệu What Is Inheritance? ppt

What Is Inheritance?
There is generally a lot of confusion among programmers as to what inheritance is. Part
of this trouble stems from the fact that the word “inheritance” itself has several subtly
different meanings. If someone bequeaths something to you in a will, you are said to
inherit it. Similarly, we say that you inherit half of your genes from your mother and half
of your genes from your father. Both of these uses of the word inheritance have very little
to do with inheritance in programming.
Inheritance in programming is all about classification—it's a relationship between
classes. For example, when you were at school, you probably learned about mammals,
and learned that horses and whales are examples of mammals. Each does everything that
a mammal does (it breathes air, gives birth to live young, and so on), but also has its own
special features (a horse has hooves, unlike a whale).
In Microsoft Visual C#, you could model this by creating two classes, one called
Mammal and one called Horse, and declare that Horse inherits from Mammal. The
inheritance would model that there is a relationship and would capture the fact that all
horses are mammals. Similarly, you could also declare a class called Whale that also
inherits from Mammal. Common functionality (such as breathing and giving birth) could
be placed in the Mammal class; properties such as hooves or fins should be placed in the
Horse or Whale class as appropriate.