Method overriding with virtual and override in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the virtual keyword do in C#?

The <code>virtual</code> keyword allows a method in a base class to be overridden in a derived class. It marks the method as extendable or replaceable.

beginner

What is the purpose of the override keyword in C#?

The <code>override</code> keyword tells the compiler that a method in a derived class is replacing a <code>virtual</code> method from its base class.

intermediate

Can a method without <code>virtual</code> in the base class be overridden with <code>override</code> in the derived class?

No. Only methods marked <code>virtual</code> (or <code>abstract</code>) in the base class can be overridden using <code>override</code> in the derived class.

intermediate

What happens if you call a virtual method on a base class reference that points to a derived class object?

The overridden method in the derived class is called. This is called polymorphism and allows behavior to change based on the actual object type.

beginner

Show a simple example of method overriding using virtual and override.

Example:<br><pre>class Animal {
  public virtual void Speak() {
    Console.WriteLine("Animal speaks");
  }
}
class Dog : Animal {
  public override void Speak() {
    Console.WriteLine("Dog barks");
  }
}</pre>

Which keyword marks a method in the base class to allow overriding?

A virtual

B override

C new

D abstract

The virtual keyword marks a method as overridable in the base class.

What keyword do you use in the derived class to replace a base class virtual method?

A virtual

B new

C override

D sealed

The override keyword replaces the base class virtual method in the derived class.

If a base class method is not virtual, what happens if you try to override it?

A Compiler error

B It overrides successfully

C Runs base method anyway

D Method is hidden but not overridden

You get a compiler error because only virtual or abstract methods can be overridden.

Calling a virtual method on a base class reference that points to a derived object calls:

A Base class method

B Derived class overridden method

C Compiler error

D Random method

The derived class overridden method is called due to polymorphism.

Which keyword prevents further overriding of a virtual method?

A virtual

B override

C abstract

D sealed

The sealed keyword stops further overriding of a virtual method.

Explain how method overriding works using virtual and override keywords in C#.

Think about how a base class method can be changed in a child class.

Describe what happens if you call a virtual method on a base class reference that points to a derived class object.

Focus on which method actually runs at runtime.