How do keywords virtual and override work?

Consider the following classes:

public class A {
  public void test() {
    Console.WriteLine("This is class A");
  }
}
public class B : A {
  public void test() {
    Console.WriteLine("This is class B");
  }
}

Now if you initialize the variables:

A a = new A();
A b = new B(); // Note that the type is A not B

a.test(); // This is class A
b.test(); // This is class A (calls base class's function)

Also it throws a warning:

warning CS0108: 'B.test()' hides inherited member 'A.test()'

In order to override the function, A’s test will have to be marked as virtual and override keyword is required for B’s test:

public class A {
    public virtual void test() {
        Console.WriteLine("This is class A");
    }
}
public class B : A {
    public override void test() {
        Console.WriteLine("This is class B");
    }
}

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• Tag: csharp