Default interface methods in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are default interface methods in C#?

Default interface methods allow interfaces to provide a default implementation for methods. This means classes implementing the interface don't have to implement those methods unless they want to override the default behavior.

beginner

How do you declare a default method in an interface?

Inside the interface, you define the method with a body using curly braces. For example:<br>

interface IExample { void Show() { Console.WriteLine("Hello"); } }

beginner

Can a class override a default interface method?

Yes, a class implementing the interface can provide its own implementation of the default method, which will replace the default one.

intermediate

Why were default interface methods introduced in C#?

They were introduced to allow adding new methods to interfaces without breaking existing implementations. This helps evolve interfaces over time.

intermediate

What happens if a class implements two interfaces with the same default method signature?

The class must explicitly implement the method to resolve the conflict, otherwise the compiler will give an error.

What is the main benefit of default interface methods?

A Allow interfaces to have method implementations

B Make interfaces abstract classes

C Prevent classes from implementing interfaces

D Remove the need for interfaces

Default interface methods allow interfaces to provide method implementations, so classes don't always have to implement them.

How do you provide a default implementation in an interface method?

A By declaring the method without a body

B By declaring the method with a body inside the interface

C By implementing the method in the class only

D By using abstract keyword

Default implementations are given by writing the method with a body inside the interface.

If a class implements an interface with a default method, what happens if the class does not implement that method?

A Runtime exception

B Compiler error

C Method is ignored

D Class uses the default method implementation

The class automatically uses the default implementation provided by the interface.

Can default interface methods access private members of the implementing class?

A Yes, always

B Only if marked internal

C No, they cannot access private members

D Only if class is sealed

Default interface methods cannot access private members of the implementing class.

What must a class do if it implements two interfaces with conflicting default methods?

A Explicitly implement the conflicting method

B Nothing, compiler resolves automatically

C Remove one interface

D Mark class as abstract

The class must explicitly implement the method to resolve the conflict.

Explain what default interface methods are and why they are useful.

Think about how interfaces used to work before default methods.

Describe how a class can override a default interface method and what happens if it does not.

Consider what happens when you want to change the default behavior.