Polymorphism

[ychhuong]

I have read the book about OOP. It is said that Polymorphism is the ability to have the same method(the same name) in many classes.

I want to know that if I create two classes and each class has the same print method without using Inheritance or Interface. Is it called Polymorphism or not?

[jmcilhinney]

A polymorphic method is one that is declared in one class and overridden in another. If two methods in different classes have the same name but no other relationship then that is not polymorphism.

[penagate]

Either method overriding, or the ability to implement the same interface method differently, are considered polymorphism.

[ychhuong]

Thank jmcilhinney and penagate.

Sometimes my problem has been solved, but I want to get more ideas about this. And I also don't know how to mark it as resolved.

[penagate]

Maybe the FAQ can help you

[wossname]

class Parrot
public sub Speak()
...
end class
 
class Human
public sub Speak()
...
end class

This is NOT polymorphism because the two classes are totally unrelated.

However...

Class Mammal
        Public Overridable Sub Speak()
        End Sub
    End Class
 
    Class Human
        Inherits Mammal
        Public Overrides Sub Speak()
        End Sub
    End Class

IS polymorphism because Speak can be called on either a mammal (monkey say "ook") or a Human ("Hi, I'm a car salesman") without the compiler necessarily knowing at runtime which class type an object will be.

This also shows inheritance.

[nkad]

Exactly! My professor keeps say that "Polymorphism is the ability to have the same method(the same name) in many classes."

This could only be the case when inheritance is used, like the example wossname has shown.