Runtime polymorphism execution in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of overridden method call

What is the output of this C# program when calling the Speak method on a base class reference pointing to a derived class object?

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

A Dog barks

B Animal speaks

C Compile-time error

D Runtime exception

💡 Hint

Remember that virtual methods allow the derived class to provide its own implementation that is called at runtime.

The Speak method is marked as virtual in the base class and overridden in the derived class. When calling Speak on a base class reference that points to a derived class object, the derived class's method runs, printing "Dog barks".

❓ Predict Output

intermediate

Output of method hiding vs overriding

What will be printed when running this C# code?

C Sharp (C#)

using System;

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

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

class Program {
    static void Main() {
        Base obj = new Derived();
        obj.Show();
    }
}

A Derived Show

B Runtime exception

C Compile-time error

D Base Show

💡 Hint

The new keyword hides the base method but does not override it.

Because Show in Derived hides the base method instead of overriding it, calling Show on a base class reference calls the base class method, printing "Base Show".

🔧 Debug

advanced

Identify runtime error in polymorphic call

What runtime error will this C# code produce when executed?

C Sharp (C#)

using System;

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

class Cat : Animal {
    public override void Speak() {
        throw new InvalidOperationException("Cat cannot speak now");
    }
}

class Program {
    static void Main() {
        Animal pet = new Cat();
        pet.Speak();
    }
}

A InvalidOperationException with message "Cat cannot speak now"

B NullReferenceException

C No error, prints "Animal speaks"

D Compile-time error

💡 Hint

Check what the overridden method in the derived class does.

The Speak method in Cat throws an InvalidOperationException. Since the base class reference points to a Cat object, calling Speak runs the overridden method and throws the exception.

🧠 Conceptual

advanced

Effect of sealed override on runtime polymorphism

Consider this C# code snippet. What will be the output when calling Speak on a Base reference to a Derived2 object?

C Sharp (C#)

using System;

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

class Derived1 : Base {
    public sealed override void Speak() {
        Console.WriteLine("Derived1 speaks");
    }
}

class Derived2 : Derived1 {
    public override void Speak() {
        Console.WriteLine("Derived2 speaks");
    }
}

class Program {
    static void Main() {
        Base obj = new Derived2();
        obj.Speak();
    }
}

A Derived2 speaks

B Derived1 speaks

C Compile-time error

D Base speaks

💡 Hint

Check what the sealed keyword does to method overriding.

The Speak method in Derived1 is sealed, so Derived2 cannot override it. Attempting to override causes a compile-time error.

❓ Predict Output

expert

Output of polymorphic method with base call

What is the output of this C# program?

C Sharp (C#)

using System;

class Vehicle {
    public virtual void Start() {
        Console.WriteLine("Vehicle started");
    }
}

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

class Program {
    static void Main() {
        Vehicle v = new Car();
        v.Start();
    }
}

A Car started

B

Vehicle started
Car started

C Vehicle started

D Compile-time error

💡 Hint

The derived method calls the base method before printing its own message.

The Start method in Car calls base.Start() which prints "Vehicle started", then prints "Car started". So both lines appear in order.