Runtime polymorphism execution in C Sharp (C#) - Step-by-Step Execution

Concept Flow - Runtime polymorphism execution

Create base class reference

↓

Assign derived class object

↓

Call overridden method

↓

Runtime decides which method to run

↓

Derived class method runs if overridden

↓

Output result

↓

End

At runtime, the program decides which method to call based on the actual object type, enabling dynamic behavior.

Execution Sample

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 a = new Dog();
    a.Speak();
  }
}

This code shows a base class Animal and a derived class Dog overriding Speak(). The call a.Speak() runs Dog's Speak() because a refers to a Dog object.

Execution Table

Step	Action	Object Type	Method Called	Output
1	Create Animal reference 'a' and assign new Dog()	Dog	N/A	N/A
2	Call a.Speak()	Dog	Dog.Speak()	Dog barks
3	End of execution	Dog	N/A	N/A

💡 Execution stops after calling the overridden method on the Dog object.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
a	null	Dog object reference	Dog object reference	Dog object reference

Key Moments - 2 Insights

Why does calling a.Speak() run Dog's Speak() and not Animal's?

Because 'a' refers to a Dog object at runtime, the overridden Dog.Speak() method is called, as shown in execution_table step 2.

What if Dog did not override Speak()?

Then calling a.Speak() would run Animal's Speak() method, since no override exists. This is implied by the runtime method selection in the flow.

Visual Quiz - 3 Questions

Look at the execution_table, what is the type of object 'a' after step 1?

A Animal

B null

C Dog

D Object

💡 Hint

Check the 'Object Type' column in execution_table row 1.

At which step is the overridden method Dog.Speak() called?

A Step 2

B Step 1

C Step 3

D Never

💡 Hint

Look at the 'Method Called' column in execution_table.

If 'a' was assigned new Animal() instead of new Dog(), what method would be called at step 2?

A Dog.Speak()

B Animal.Speak()

C No method

D Compile error

💡 Hint

Runtime method depends on actual object type, see concept_flow and key_moments.

Concept Snapshot

Runtime polymorphism means the program decides which method to run based on the actual object type at runtime.
Use 'virtual' in base class and 'override' in derived class.
A base class reference can point to a derived class object.
Calling an overridden method runs the derived class version.
This enables flexible and dynamic behavior.

Full Transcript

This example shows runtime polymorphism in C#. We have a base class Animal with a virtual method Speak. The derived class Dog overrides Speak. We create a base class reference 'a' and assign it a new Dog object. When we call a.Speak(), the program checks the actual object type at runtime, which is Dog, and runs Dog's Speak method. The execution table shows the steps: creating the reference, calling the method, and ending. The variable tracker shows 'a' holds a Dog object after assignment. Key moments clarify why the derived method runs and what happens if no override exists. The quiz tests understanding of object type, method call step, and behavior if the object type changes. Runtime polymorphism allows flexible code that adapts behavior based on actual objects during execution.