Sealed classes and methods in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of sealed class inheritance attempt

What will be the output or result of this C# code?

C Sharp (C#)

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

class Dog : Animal {
}

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

A Compilation error: method 'Speak' is sealed

B Animal speaks

C Runtime error: method not found

D Compilation error: cannot derive from sealed class 'Animal'

💡 Hint

Remember what sealed means for classes in C#.

A sealed class cannot be inherited. Trying to derive Dog from sealed Animal causes a compile-time error.

❓ Predict Output

intermediate

Output of sealed method override attempt

What will be the output or result of this C# code?

C Sharp (C#)

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

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

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

class Program {
    static void Main() {
        SportsCar sc = new SportsCar();
        sc.Start();
    }
}

A Vehicle started

B Compilation error: cannot override sealed method 'Start'

C Car started

D SportsCar started

💡 Hint

Check what sealed means when applied to methods.

A sealed override method cannot be further overridden. SportsCar's attempt to override Start causes a compile-time error.

🧠 Conceptual

advanced

Purpose of sealed keyword in C#

Which of the following best describes the purpose of the sealed keyword in C#?

A To prevent a class from being inherited or a method from being overridden further

B To make a class abstract and force implementation in derived classes

C To allow multiple inheritance of classes

D To mark a method as asynchronous

💡 Hint

Think about what sealed restricts in inheritance.

Sealed prevents further inheritance of classes or overriding of methods, ensuring fixed behavior.

❓ Predict Output

advanced

Output of sealed method call via base reference

What will be the output of this C# program?

C Sharp (C#)

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

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

class MoreDerived : Derived {
    // No override here
}

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

A Base Show

B Compilation error: cannot override sealed method

C Derived Show

D Runtime error: method not found

💡 Hint

Consider which method is called when sealed override exists and no further override.

The sealed override in Derived stops further overrides. MoreDerived uses Derived's Show method. The call prints 'Derived Show'.

🔧 Debug

expert

Identify the error in sealed method usage

What error will this C# code produce?

C Sharp (C#)

class Parent {
    public virtual void Display() {
        System.Console.WriteLine("Parent Display");
    }
}

class Child : Parent {
    public sealed override void Display() {
        System.Console.WriteLine("Child Display");
    }
}

class GrandChild : Child {
    public override void Display() {
        System.Console.WriteLine("GrandChild Display");
    }
}

class Program {
    static void Main() {
        GrandChild gc = new GrandChild();
        gc.Display();
    }
}

A Compilation error: cannot override sealed method 'Display' in 'Child'

B GrandChild Display

C Runtime error: method dispatch failed

D Child Display

💡 Hint

Check the rules about overriding sealed methods.

The method Display in Child is sealed, so GrandChild cannot override it. This causes a compile-time error.