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polymorphism interview questions and answers in c#

Question: What is polymorphism in c#?
Answer: Polymorphism means one object behaving as multiple forms. One object or function shows different behavior in the different scenario is called polymorphism. For example, Dilip is a human object or function in which talking behavior will change according to his Father, Mother, Son, Boss, etc.
In C# there are two types of polymorphism
1.  Static or Compile time
·         Function Overloading
·         operator overloading
2.  Run Time
·         Virtual function

Question: What is method overloading?
Answer: When a class has more than one method with the same but different signature is called method overloading.
For example:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{

    class A
    {
       //1- Passed string parameter
        public void Add(string a, string b)
        {
            a = a + b;
            Console.WriteLine(a);
        }
       //2- Passed int parameter
        public void Add(int a, int b)
        {
            a = a + b;
            Console.WriteLine(a);
        }
        static void Main(string[] args)
        {
            A oA = new A();
            oA.add("Dilip","Singh");
            oA.add(10, 15);
        }
    }
}

Output:
DilipSingh
25

In the above example, Add is the same-named function but the parameter is different so when we call the Add method passing parameter as a string then the Add method with string parameter will access the same as Add method with int parameter.

Question: What is method overriding?
Answer: To extend or modify the abstract or virtual implementation of the inherited method, property, indexer or event is called overriding.
For example:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{

    class Demo
    {
        static void Main(string[] args)
        {
            A oA;
            oA = new A();
            oA.Display();
            oA = new B();
            oA.Display();
        }
    }
    class A
    {
        public virtual void Display()
        {
            Console.WriteLine("Base class");
        }
    }
    class B : A
    {
        public override void Display()
        {
            Console.WriteLine("Derived class");
        }
    }
}

Question: When should use method overloading?
 Answer:  When more than one method does the same thing but take different parameter. eg Method Area(circle c). Area(Rectangle r).. the basic function is calculating area but with a different structures.

Question: Advantage of Polymorphism?
Answer:
·         Invoking child class functions dynamically
·         Maintenance of code becomes easy.

Question: What is the difference between "new" and "override" keyword in the inheritance chain?
Answer:  Override: When a method of a base class is overridden in a derived class, the version in the derived class is used, even if the calling code didn't "know" that the object was an instance of the derived class.

New: If you use the new keyword instead of override, the method in the derived class doesn't override the method in the base class, it merely hides it.


Question: Will the following code will compile? Why?
Answer:
A) class A
    {
        public  void Display()
        {
            Console.WriteLine("Base class");
        }
    }
    class B : A
    {
        public override void Display()
        {
            Console.WriteLine("Derived class");
        }
    }

The above code will not compile, because the base class method should be marked with a virtual class.
B)
class A
    {
        public void Display()
        {
            Console.WriteLine("Base class");
        }
    }
    class B : A
    {
        public new void Display()
        {
            Console.WriteLine("Derived class");
        }
    }
Yes above code will be compile because new keyword defines its own implementation and it's not related to base class method in any way.
C)
class A
    {
        public virtual void Display(ref int a)
        {
            Console.WriteLine("Base class");
        }
    }
    class B : A
    {
        public override void Display(out int a)
        {
            Console.WriteLine("Derived class");
        }
    }
Above code will give compile time error due to signature mismatch.
Question: What is the disadvantage of using a virtual keyword?
Answer:
1.       Appropriate function calls are determined only at runtime.

2.       Since virtual keyword is used derived classes may ignore that base class implementation.