Interface declaration syntax in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an interface in C#?

An interface in C# is a contract that defines a set of methods and properties without implementing them. Classes or structs that implement the interface must provide the implementation.

beginner

How do you declare an interface in C#?

Use the interface keyword followed by the interface name and a block containing method/property signatures. For example:<br>

public interface IExample { void DoWork(); }

intermediate

Can interfaces contain fields or constructors in C#?

No, interfaces cannot contain fields or constructors. They only declare method, property, event, or indexer signatures without implementation.

intermediate

What access modifier is used for interface members in C#?

Interface members are implicitly public and cannot have access modifiers. All members declared in an interface are public by default.

beginner

How does a class implement an interface in C#?

A class implements an interface by using a colon <code>:</code> followed by the interface name, then providing implementations for all interface members. Example:<br><pre>public class Worker : IExample { public void DoWork() { /* code */ } }</pre>

Which keyword is used to declare an interface in C#?

A interface

B class

C struct

D implements

The interface keyword is used to declare an interface in C#.

Can an interface in C# contain method implementations?

A Yes, always

B Only default interface methods (C# 8.0+)

C Only private methods

D No, never

Starting with C# 8.0, interfaces can have default implementations for methods, but traditionally interfaces only declare signatures.

What access modifier do interface members have by default?

A public

B protected

C private

D internal

Interface members are implicitly public and cannot have other access modifiers.

How does a class indicate it implements an interface?

A Using the keyword 'inherits'

B Using the keyword 'implements'

C Using a colon ':' followed by the interface name

D Using angle brackets '<>'

In C#, a class implements an interface by using a colon ':' followed by the interface name.

Which of these can NOT be declared inside an interface?

A Events

B Properties

C Method signatures

D Fields

Interfaces cannot contain fields; they only declare signatures for methods, properties, events, and indexers.

Explain how to declare an interface in C# and how a class implements it.

Think about the contract nature of interfaces and how classes fulfill that contract.

What are the limitations of interfaces in C# regarding members they can contain?

Consider what an interface represents and what it cannot do.