C# Inheritance Doubt

Question

3.00/5 (3 votes)

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Hi,
I have a doubt . When can a base class reference store derived class object and vice versa.
Like what will be the output of this and why?

C#

class A
    {
        public void x()
        {
            Console.WriteLine("hi");
        }
    }
    class B : A
    {
        public void y()
        {
            Console.WriteLine("hello");
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            A a = new B();
B b =new A();
b.x();
            a.y();
        }
    }

Posted 2-Dec-11 8:05am

manish.netbug

Updated 2-Dec-11 8:07am

v2

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Wonde Tadesse 2-Dec-11 14:17pm

B b =new A();// Compile error, B is a sub type of A not vice versa

2 solutions

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OriginalGriff · Accepted Answer · 2011-12-02T08:10:00

Your code will not compile.

C#

B b = new A();

Is not allowed, because B is derived from A and not the other way around. If the compiler allowed this,
then you could say:

C#

B b = new A();
b.y();

But what would happen at run time? The "y" method is not defined for objects of class A, so the method could not be called. The compiler prevents this run time error by refusing to let you make a design time assignment that would cause the problem.

It's a bit like saying a Ford is a Car, so every Car has a Ford badge - which is nonsense.

#realJSOP · Accepted Answer · 2011-12-02T08:24:00

Solution 2

Why don't you run it under the debugger and see for yourself?

Posted 2-Dec-11 8:24am

#realJSOP

Comments

OriginalGriff 2-Dec-11 14:39pm

Because it won't compile...:laugh:

Nikil S 2-Dec-11 16:27pm

May be he wants to quiz us and also wants to know the reason behind the error.