Method overriding with virtual and override in C Sharp (C#) - Mini Project: Build & Apply

Method overriding with virtual and override

📖 Scenario: Imagine you are creating a simple program to show different types of animals making sounds. Each animal has a method to make a sound, but the exact sound depends on the animal type.

🎯 Goal: You will build a base class Animal with a virtual method MakeSound(). Then, you will create a derived class Dog that overrides MakeSound() to show a dog-specific sound. Finally, you will print the sounds from both classes.

📋 What You'll Learn

Create a base class Animal with a virtual method MakeSound() that prints "Some generic animal sound".

Create a derived class Dog that overrides the MakeSound() method to print "Bark!".

Create an instance of Animal and call MakeSound().

Create an instance of Dog and call MakeSound().

Print the outputs exactly as specified.

💡 Why This Matters

🌍 Real World

Method overriding is used in many programs to allow different objects to behave differently while sharing the same method name. For example, different animals making different sounds.

💼 Career

Understanding virtual and override keywords is essential for object-oriented programming jobs, especially when working with inheritance and polymorphism in C#.

1

Create the base class with a virtual method

Create a class called Animal with a public virtual method MakeSound() that prints exactly "Some generic animal sound".

C Sharp (C#)

// Your code here

Hint

Use the virtual keyword to allow the method to be overridden later.

2

Create the derived class that overrides the method

Create a class called Dog that inherits from Animal. Override the MakeSound() method using the override keyword to print exactly "Bark!".

C Sharp (C#)

using System;

class Animal
{
    public virtual void MakeSound()
    {
        Console.WriteLine("Some generic animal sound");
    }
}

// Your code here

Hint

Use class Dog : Animal to inherit and override to change the method.

3

Create instances and call the methods

Create an instance called animal of type Animal and call animal.MakeSound(). Then create an instance called dog of type Dog and call dog.MakeSound().

C Sharp (C#)

using System;

class Animal
{
    public virtual void MakeSound()
    {
        Console.WriteLine("Some generic animal sound");
    }
}

class Dog : Animal
{
    public override void MakeSound()
    {
        Console.WriteLine("Bark!");
    }
}

// Your code here

Hint

Create objects and call the methods exactly as shown.

4

Print the output

Run the program and print the output of calling MakeSound() on both animal and dog. The output should be exactly two lines: first "Some generic animal sound", then "Bark!".

C Sharp (C#)

using System;

class Animal
{
    public virtual void MakeSound()
    {
        Console.WriteLine("Some generic animal sound");
    }
}

class Dog : Animal
{
    public override void MakeSound()
    {
        Console.WriteLine("Bark!");
    }
}

class Program
{
    static void Main()
    {
        Animal animal = new Animal();
        animal.MakeSound();

        Dog dog = new Dog();
        dog.MakeSound();
    }

    // Your code here
}

Hint

Make sure the output matches exactly with no extra spaces or lines.

Practice

1. What keyword in C# allows a method in a base class to be changed by a derived class?

easy

A. new

B. override

C. virtual

D. abstract

Solution

1. Step 1: Understand base class method flexibility

   The virtual keyword marks a method in the base class as changeable by derived classes.

2. Step 2: Differentiate from other keywords

   override is used in derived classes, new hides methods, and abstract requires implementation.

3. Final Answer:

   virtual -> Option C

4. Quick Check:

   Base method change = virtual [OK]

Hint: Base class method change uses virtual keyword [OK]

Common Mistakes:

• Confusing override with virtual
• Using new instead of virtual for overriding
• Thinking abstract allows method change without implementation

2. Which of the following is the correct syntax to override a virtual method named Display in a derived class?

easy

A. public void Display() { }

B. public virtual void Display() { }

C. public new void Display() { }

D. public override void Display() { }

Solution

1. Step 1: Identify override syntax

   To change a virtual method in a derived class, use override before the method signature.

2. Step 2: Eliminate other options

   The plain public void Display() { } lacks the override keyword, public virtual void Display() { } incorrectly uses virtual in the derived class, and public new void Display() { } hides the base method but doesn't override it for polymorphism.

3. Final Answer:

   public override void Display() { } -> Option D

4. Quick Check:

   Override method uses override keyword [OK]

Hint: Override methods must use override keyword [OK]

Common Mistakes:

• Omitting override keyword in derived class
• Using virtual instead of override in derived class
• Using new keyword instead of override

3. What will be the output of the following code?

class Animal {
  public virtual string Speak() { return "Animal sound"; }
}
class Dog : Animal {
  public override string Speak() { return "Bark"; }
}
class Cat : Animal {
  public override string Speak() { return "Meow"; }
}

Animal a = new Dog();
Animal b = new Cat();
Console.WriteLine(a.Speak());
Console.WriteLine(b.Speak());

medium

A. Bark
Meow

B. Animal sound
Animal sound

C. Bark
Animal sound

D. Animal sound
Meow

Solution

1. Step 1: Understand virtual and override behavior

   Because Speak is virtual and overridden, the derived class method runs even when referenced as base type.

2. Step 2: Trace the output calls

   a is a Dog instance, so Speak() returns "Bark"; b is a Cat instance, so it returns "Meow".

3. Final Answer:

   Bark Meow -> Option A

4. Quick Check:

   Override method output = Bark, Meow [OK]

Hint: Virtual method calls use derived override at runtime [OK]

Common Mistakes:

• Expecting base class method output
• Ignoring override effect on base class reference
• Confusing new keyword behavior with override

4. Identify the error in this code snippet:

class Base {
  public virtual void Show() { Console.WriteLine("Base"); }
}
class Derived : Base {
  public void Show() { Console.WriteLine("Derived"); }
}

Base obj = new Derived();
obj.Show();

medium

A. No error; output is Base

B. No error; output is Derived

C. Compile-time error: missing override keyword

D. Runtime error: method not found

Solution

1. Step 1: Check method overriding rules

   The derived class method Show does not use override, so it hides the base method instead of overriding.

2. Step 2: Determine method called by base reference

   Because Show is virtual in base but not overridden, calling obj.Show() calls base class method, outputting "Base".

3. Final Answer:

   No error; output is Base -> Option A

4. Quick Check:

   Missing override means base method runs [OK]

Hint: Override keyword needed to replace virtual method [OK]

Common Mistakes:

• Assuming method hides override automatically
• Expecting Derived output without override
• Thinking missing override causes compile error

5. Given the classes below, what will be the output?

class Vehicle {
  public virtual string Describe() => "Vehicle";
}
class Car : Vehicle {
  public override string Describe() => "Car";
}
class SportsCar : Car {
  public new string Describe() => "SportsCar";
}

Vehicle v = new SportsCar();
Car c = new SportsCar();
SportsCar s = new SportsCar();

Console.WriteLine(v.Describe());
Console.WriteLine(c.Describe());
Console.WriteLine(s.Describe());

hard

A. Vehicle
Car
SportsCar

B. Car
Car
SportsCar

C. Vehicle
Vehicle
Vehicle

D. SportsCar
SportsCar
SportsCar

Solution

1. Step 1: Understand new vs override

   SportsCar uses new to hide Describe, not override it. So base class virtual dispatch applies only up to Car.

2. Step 2: Trace each call

   v.Describe() calls Vehicle reference to SportsCar instance, but virtual dispatch stops at Car override, so returns "Car".
   c.Describe() calls Car reference to SportsCar, same as above, returns "Car".
   s.Describe() calls SportsCar reference, so calls hidden method returning "SportsCar".

3. Final Answer:

   Car Car SportsCar -> Option B

4. Quick Check:

   new hides method, override dispatches virtual [OK]

Hint: new hides method; override participates in virtual dispatch [OK]

Common Mistakes:

• Expecting new method to override virtual dispatch
• Confusing new with override behavior
• Assuming base reference calls hidden method