Difference between new and override

Question

Wondering what the difference is between the following:

Case 1: Base Class

public void DoIt();

Case 1: Inherited class

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Answer 1

The functional difference will not be show in these tests:

BaseClass bc = new BaseClass();

bc.DoIt();

DerivedClass dc = new DerivedClass();

dc.ShowIt();

In this exmample, the Doit that is called is the one you expect to be called.

In order to see the difference you have to do this:

BaseClass obj = new DerivedClass();

obj.DoIt();

You will see if you run that test that in the case 1 (as you defined it), the DoIt() in BaseClass is called, in case 2 (as you defined it), the DoIt() in DerivedClass is called.

Answer 2

At the first case it will call derived class DoIt() method because new keyword hides base class DoIt() method.

At the second case it will call overriden DoIt()

  public class A
{
    public virtual void DoIt()
    {
        Console.WriteLine("A::DoIt()");
    }
}

public class B : A
{
    new public void DoIt()
    {
        Console.WriteLine("B::DoIt()");
    }
}

public class C : A
{
    public override void DoIt()
    {
        Console.WriteLine("C::DoIt()");
    }
}

let create instance of these classes

   A instanceA = new A();

    B instanceB = new B();
    C instanceC = new C();

    instanceA.DoIt(); //A::DoIt()
    instanceB.DoIt(); //B::DoIt()
    instanceC.DoIt(); //B::DoIt()

Everything is expected at above. Let set instanceB and instanceC to instanceA and call DoIt() method and check result.

    instanceA = instanceB;
    instanceA.DoIt(); //A::DoIt() calls DoIt method in class A

    instanceA = instanceC;
    instanceA.DoIt();//C::DoIt() calls DoIt method in class C because it was overriden in class C