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Mastering C# for .NET Developers

Virtual Methods and Properties

Explore how to override virtual methods and properties in C# to customize behavior in derived classes. Understand using the base keyword to extend functionality and the sealed keyword to prevent further overriding, helping you master inheritance and polymorphism in object-oriented C# programming.

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When we inherit a method from a base class, we might need to change its behavior in a child class. Consider the following example:

public class Animal
{
    public void Voice()
    {
        // Method implementation
    }
}
A simple base class

Suppose the Voice() method produces the voice of an animal. For something as generic as the Animal class, we could have a generic implementation of this method. However, derived classes like Cat or Dog require specific implementations of the Voice() method. For example, cats meow and dogs bark.

Providing a different implementation for an inherited method is called overriding. In C#, we can only override a method if it was marked as virtual in a base class.

Overriding a method

We have three classes: Animal, Cat, and Dog. The latter two classes inherit the Voice() method from Animal but override it with different implementations.

First, let's look at the base class where the method is defined.

C# 14.0
namespace VirtualMethodsAndProperties;
public class Animal
{
    // Marked the method as virtual
    // This method can be overridden in child classes
    public virtual void Voice()
    {
        Console.WriteLine("Grrrrr");
    }
}

  • Line 1: We declare a file-scoped namespace.

  • Line 7: We use the virtual keyword to allow derived classes to override the Voice method.

  • Line 9: We provide a default implementation that prints “Grrrrr”.

Now that we have a base class with a virtual method, we can ...