Implementing interfaces 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 that implement the interface must provide the implementation for all its members.

beginner

How do you declare that a class implements an interface in C#?

You use a colon (:) after the class name followed by the interface name. For example: <br><code>public class MyClass : IMyInterface { }</code>

intermediate

Can a class implement multiple interfaces in C#? How?

Yes, a class can implement multiple interfaces by listing them separated by commas after the colon. For example:<br><code>public class MyClass : IFirst, ISecond { }</code>

intermediate

What happens if a class does not implement all members of an interface it declares?

The C# compiler will give an error because the class must provide implementations for all interface members unless the class is declared abstract.

advanced

Explain explicit interface implementation in C#.

Explicit interface implementation means implementing interface members so they can only be accessed through the interface, not the class instance directly. This is done by prefixing the member with the interface name, like:<br><code>void IMyInterface.Method() { }</code>

How do you declare that a class implements an interface named IExample?

A public class MyClass : IExample { }

B public interface MyClass : IExample { }

C public class MyClass implements IExample { }

D public class MyClass inherits IExample { }

In C#, a class implements an interface using a colon (:), not 'implements' or 'inherits'.

What must a class do when it implements an interface?

A Implement none of the interface members

B Implement at least one interface member

C Implement all interface members

D Only declare the interface name

A class must implement all members of the interface unless it is abstract.

Can a class implement more than one interface?

A Yes, but only if interfaces inherit each other

B Yes, by separating interface names with commas

C No, only one interface is allowed

D No, interfaces cannot be implemented

C# allows multiple interfaces to be implemented by listing them separated by commas.

What is explicit interface implementation used for?

A To implement interface members with different names

B To make interface members public

C To inherit from multiple classes

D To hide interface members from the class's public API

Explicit implementation hides interface members so they are accessible only through the interface type.

If a class does not implement all interface members, what happens?

A Compilation error unless the class is abstract

B The program runs but with warnings

C The missing members are auto-implemented

D The interface is ignored

The compiler requires all interface members to be implemented unless the class is abstract.

Describe how to implement an interface in a C# class and what rules must be followed.

Think about the syntax and what the compiler expects.

Explain the difference between implicit and explicit interface implementation in C#.

Consider how you access the implemented methods.