CSC/ECE 517 Fall 2011/ch1 1i lj

CSC/ECE 517 Fall 2010/ch1 1i lj

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Overriden Method

Method overriding[1], in object oriented programming, is a language feature that allows a subclass to provide a specific implementation of a method that is already provided by one of its superclasses. The implementation in the subclass overrides (replaces) the implementation in the superclass.

C++

In native C++, a derived class function having the same name and parameters as a base class virtual function will *always* override it. In C++/CLI you have the option of using the new contextual keyword to specify whether you want to override a base class function or hide it. Example:

ref class Base
{
public:
    virtual void Goo()
    {
        Show("Base::Goo");
    }
    
    virtual void Boo()
    {
        Show("Base::Boo");
    }
    
    virtual void Doo()
    {
        Show("Base::Doo");
    }
};

ref class Derived : Base
{
public:
    //Overrides Base::Goo

    virtual void Goo()
    {
        Show("Derived::Goo");
    }
    
    //Overrides Base::Boo as above

    virtual void Boo() = Base::Boo
    {
        Show("Derived::Boo");
    }
    
    //Hides Base::Doo

    virtual void Doo() new
    {
        Show("Derived::Doo");
    }
};

Here's some sample code that invokes the above methods on a Base handle referencing a Derived object.

void _tmain()
{
    Base^ r = gcnew Derived();
    r->Goo();
    r->Boo();
    r->Doo();
}

You'll get the following output :-

Derived::Goo
Derived::Boo
Base::Doo