Why polymorphism matters in C Sharp (C#) - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of polymorphic method call

What is the output of this C# code demonstrating polymorphism?

C Sharp (C#)

using System;

class Animal {
    public virtual void Speak() {
        Console.WriteLine("Animal speaks");
    }
}

class Dog : Animal {
    public override void Speak() {
        Console.WriteLine("Dog barks");
    }
}

class Cat : Animal {
    public override void Speak() {
        Console.WriteLine("Cat meows");
    }
}

class Program {
    static void Main() {
        Animal myAnimal = new Dog();
        myAnimal.Speak();
    }
}

A Dog barks

B Animal speaks

C Cat meows

D Compilation error

💡 Hint

Look at which class instance is assigned to the Animal variable and which Speak method is called.

The variable myAnimal is of type Animal but holds an instance of Dog. Because Speak is virtual and overridden in Dog, the Dog version runs, printing "Dog barks".

🧠 Conceptual

intermediate

Why use polymorphism?

Which of the following best explains why polymorphism is important in programming?

A It forces all classes to have the same methods with identical implementations.

B It makes programs run faster by avoiding method calls.

C It prevents inheritance between classes to avoid confusion.

D It allows objects of different types to be treated as instances of a common base type, enabling flexible and reusable code.

💡 Hint

Think about how polymorphism helps when you want to write code that works with many types of objects.

Polymorphism lets you write code that works on a base class type but actually runs the correct method for the real object type. This makes code flexible and reusable.

🔧 Debug

advanced

Identify the runtime behavior with polymorphism

What will happen when this C# program runs?

C Sharp (C#)

using System;

class Shape {
    public virtual void Draw() {
        Console.WriteLine("Drawing a shape");
    }
}

class Circle : Shape {
    public new void Draw() {
        Console.WriteLine("Drawing a circle");
    }
}

class Program {
    static void Main() {
        Shape s = new Circle();
        s.Draw();
    }
}

A Compilation error due to 'new' keyword

B Drawing a circle

C Drawing a shape

D Runtime error

💡 Hint

Consider the difference between 'override' and 'new' keywords in method declarations.

The Draw method in Circle uses new instead of override. This hides the base method rather than overriding it. Since s is of type Shape, the base class method runs, printing "Drawing a shape".

📝 Syntax

advanced

Which code snippet correctly implements polymorphism?

Select the code snippet that correctly uses polymorphism with method overriding in C#.

A class Base { public virtual void Show() { } } class Derived : Base { public override void Show() { } }

B class Base { public virtual void Show() { } } class Derived : Base { public new void Show() { } }

C class Base { public void Show() { } } class Derived : Base { public void Show() { } }

D abstract class Base { public abstract void Show(); } class Derived : Base { public override void Show() { } }

💡 Hint

Look for the correct use of 'virtual' and 'override' keywords for polymorphism.

Option A correctly declares the base method as virtual and the derived method as override, enabling polymorphism.

Option A lacks virtual/override, so no polymorphism.

Option A is valid because the base class is declared abstract and the method is abstract.

Option A uses new which hides the method, not polymorphism.

🚀 Application

expert

Polymorphism in a collection of objects

Given the following code, what will be the output when the program runs?

C Sharp (C#)

using System;
using System.Collections.Generic;

abstract class Vehicle {
    public abstract void Start();
}

class Car : Vehicle {
    public override void Start() {
        Console.WriteLine("Car started");
    }
}

class Motorcycle : Vehicle {
    public override void Start() {
        Console.WriteLine("Motorcycle started");
    }
}

class Program {
    static void Main() {
        List<Vehicle> vehicles = new List<Vehicle> { new Car(), new Motorcycle() };
        foreach (var v in vehicles) {
            v.Start();
        }
    }
}

A Vehicle started\nVehicle started

B Car started\nMotorcycle started

C Compilation error due to abstract class instantiation

D Runtime error due to missing method implementation

💡 Hint

Check how abstract methods are implemented and called on derived class instances in a list.

The list contains Car and Motorcycle objects, both overriding Start. The loop calls Start on each, printing their respective messages.