Runtime polymorphism execution in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a base class method that can be overridden.

C Sharp (C#)

public class Animal {
    public virtual void Speak() {
        Console.[1]("Animal speaks");
    }
}

Drag options to blanks, or click blank then click option'

ADisplay

BPrint

COutput

DWriteLine

Attempts:

3 left

💡 Hint

Common Mistakes

Using methods that do not exist in Console class like Print or Display.

The Console.WriteLine method prints text to the console. It is used here to show the base class message.

2fill in blank

medium

Complete the code to override the Speak method in the derived class.

C Sharp (C#)

public class Dog : Animal {
    public override void [1]() {
        Console.WriteLine("Dog barks");
    }
}

Drag options to blanks, or click blank then click option'

ASpeak

BTalk

CSound

DMakeNoise

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different method name that does not override the base method.

The derived class overrides the base class method named Speak to provide its own behavior.

3fill in blank

hard

Fix the error in calling the Speak method using a base class reference to a derived class object.

C Sharp (C#)

Animal myAnimal = new Dog();
myAnimal.[1]();

Drag options to blanks, or click blank then click option'

ABark

BTalk

CSpeak

DMakeSound

Attempts:

3 left

💡 Hint

Common Mistakes

Calling a method that only exists in the derived class or using wrong method names.

The base class reference calls the Speak method, which is overridden by the derived class. This demonstrates runtime polymorphism.

4fill in blank

hard

Fill both blanks to create a base class reference to a derived class object and call the overridden method.

C Sharp (C#)

Animal [1] = new [2]();
[1].Speak();

Drag options to blanks, or click blank then click option'

AmyAnimal

BDog

CAnimal

DanimalObj

Attempts:

3 left

💡 Hint

Common Mistakes

Using the base class name for the object creation or mismatching variable names.

The variable myAnimal is declared as type Animal but refers to a new Dog object. Calling Speak uses the overridden method in Dog.

5fill in blank

hard

Fill all three blanks to implement runtime polymorphism with two derived classes overriding the base method.

C Sharp (C#)

public class Cat : Animal {
    public override void [1]() {
        Console.WriteLine("Cat meows");
    }
}

Animal [2] = new Dog();
Animal [3] = new Cat();
[2].Speak();
[3].Speak();

Drag options to blanks, or click blank then click option'

ASpeak

BdogAnimal

CcatAnimal

DMakeSound

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong method names or inconsistent variable names.

The Cat class overrides Speak. Two variables of type Animal refer to Dog and Cat objects. Calling Speak on each shows runtime polymorphism.

Practice

1. What does runtime polymorphism in C# allow you to do?

easy

A. Create multiple instances of the same class

B. Change variable types at runtime

C. Call derived class methods through a base class reference

D. Use static methods without creating objects

Solution

1. Step 1: Understand runtime polymorphism concept

   Runtime polymorphism allows a base class reference to call methods overridden in derived classes.

2. Step 2: Identify correct behavior

   This means the actual method called depends on the object's real type, not the reference type.

3. Final Answer:

   Call derived class methods through a base class reference -> Option C

4. Quick Check:

   Runtime polymorphism = base ref calls derived method [OK]

Hint: Think: base class ref calls derived method at runtime [OK]

Common Mistakes:

• Confusing polymorphism with changing variable types
• Thinking static methods are polymorphic
• Believing polymorphism creates multiple instances

2. Which keyword is used in C# to allow a method to be overridden in a derived class?

easy

A. virtual

B. override

C. new

D. abstract

Solution

1. Step 1: Identify keyword to enable overriding

   The base class method must be marked with virtual to allow overriding.

2. Step 2: Understand roles of keywords

   override is used in derived classes, virtual in base classes.

3. Final Answer:

   virtual -> Option A

4. Quick Check:

   Base method uses virtual to allow override [OK]

Hint: Base method uses virtual; derived uses override [OK]

Common Mistakes:

• Using override in base class instead of virtual
• Confusing new keyword with override
• Thinking abstract is required for all overrides

3. What is the output of this C# code?

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

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

medium

A. Animal sound

B. Bark

C. Meow

D. Compile error

Solution

1. Step 1: Identify object type and method called

   Variable a is of type Animal but references a Dog object.

2. Step 2: Apply runtime polymorphism

   Since Speak is virtual and overridden in Dog, the Dog version runs, printing "Bark".

3. Final Answer:

   Bark -> Option B

4. Quick Check:

   Base ref calls Dog's Speak() = Bark [OK]

Hint: Base ref calls derived override method at runtime [OK]

Common Mistakes:

• Expecting base class method output
• Confusing object type with reference type
• Thinking compile error due to override

4. Identify the error in this C# code related to runtime polymorphism:

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

medium

A. Base class method must be virtual, not override

B. Derived class method cannot override base method

C. Missing semicolon after method declaration

D. No error, code is correct

Solution

1. Step 1: Check base class method declaration

   Base class method incorrectly uses override instead of virtual.

2. Step 2: Understand override rules

   Only derived classes use override; base class must use virtual to allow overriding.

3. Final Answer:

   Base class method must be virtual, not override -> Option A

4. Quick Check:

   Base method needs virtual keyword [OK]

Hint: Base method uses virtual, not override [OK]

Common Mistakes:

• Using override in base class method
• Thinking override is allowed without virtual
• Ignoring method signature correctness

5. Given these classes:

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

What is the output?

hard

A. Vehicle\nCar\nSportsCar

B. Car\nCar\nCar

C. Vehicle\nVehicle\nVehicle

D. SportsCar\nSportsCar\nSportsCar

Solution

1. Step 1: Identify actual object type for all references

   All variables v, c, and s reference a SportsCar object.

2. Step 2: Apply runtime polymorphism for Describe()

   Since Describe is overridden in SportsCar, all calls print "SportsCar" regardless of reference type.

3. Final Answer:

   SportsCar\nSportsCar\nSportsCar -> Option D

4. Quick Check:

   All calls use SportsCar override [OK]

Hint: Actual object type decides method, not reference type [OK]

Common Mistakes:

• Assuming base class method runs for base type variable
• Confusing reference type with object type
• Ignoring override in most derived class