Method overriding with virtual and override in C Sharp (C#) - Step-by-Step Execution

Concept Flow - Method overriding with virtual and override

Base class defines virtual method

↓

Derived class overrides method with override

↓

Create derived class object

↓

Call method on derived object

↓

Derived method runs, not base

↓

End

The base class marks a method as virtual. The derived class overrides it. When called on a derived object, the overridden method runs.

Execution Sample

C Sharp (C#)

using System;
class Base {
  public virtual void Show() {
    Console.WriteLine("Base Show");
  }
}
class Derived : Base {
  public override void Show() {
    Console.WriteLine("Derived Show");
  }
}
class Program {
  static void Main() {
    var obj = new Derived();
    obj.Show();
  }
}

Defines a base class method as virtual and overrides it in a derived class, then calls the method on a derived object.

Execution Table

Step	Action	Method Called	Output
1	Create Derived object	None	None
2	Call Show() on Derived object	Derived.Show()	Derived Show
3	End of execution	None	None

💡 Method call resolved to Derived.Show() because of override keyword

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
obj	null	Derived instance	Derived instance	Derived instance

Key Moments - 3 Insights

Why does calling Show() on the derived object run Derived.Show() and not Base.Show()?

Because the base method is marked virtual and the derived method uses override, the call resolves to the derived version at runtime (see execution_table step 2).

What happens if the base method is not marked virtual but the derived method uses override?

This causes a compile error because override requires the base method to be virtual or abstract.

Can you call the base class method from the derived class override?

Yes, by using base.Show() inside the derived override method to run the base version.

Visual Quiz - 3 Questions

Look at the execution table, which method runs when obj.Show() is called?

A Derived.Show()

B Base.Show()

C Both Base.Show() and Derived.Show()

D No method runs

💡 Hint

Check step 2 in the execution_table where the method called is shown

At which step is the Derived object created?

A Step 3

B Step 1

C Step 2

D No object is created

💡 Hint

Look at the Action column in execution_table for object creation

If the base method was not virtual, what would happen when compiling this code?

A It compiles and runs Derived.Show()

B It compiles and runs Base.Show()

C Compile error due to override keyword

D Runtime error

💡 Hint

Recall key_moments about override requiring virtual base method

Concept Snapshot

Use virtual keyword on base class method to allow overriding.
Use override keyword in derived class to replace base method.
Calling method on derived object runs overridden method.
Override requires base method to be virtual or abstract.
Use base.Method() to call base version inside override.

Full Transcript

In C#, method overriding lets a derived class replace a base class method's behavior. The base method must be marked with the virtual keyword. The derived class uses override to provide a new version. When you create an object of the derived class and call the method, the overridden version runs. This is shown in the example where Base.Show() is virtual and Derived.Show() overrides it. The execution table shows the derived method runs when called. If the base method is not virtual, using override causes a compile error. You can also call the base method from inside the override using base.Show(). This mechanism helps customize behavior in subclasses while keeping a common interface.