Learn C#: Interfaces and Inheritance

Organize, secure, and simplify your code with interfaces and inheritance.

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Key Concepts

Review core concepts you need to learn to master this subject

C# Interface

C# Inheritance

C# protected Keyword

C# override/virtual Keywords

C# abstract Keyword

C# Interface

interface IAutomobile
{
  string LicensePlate { get; }
  double Speed { get; }
  int Wheels { get; }
}

// The IAutomobile interface has three properties. Any class that implements this interface must have these three properties.

public interface IAccount
{
  void PayInFunds ( decimal amount );
  bool WithdrawFunds ( decimal amount );
  decimal GetBalance ();
}

// The IAccount interface has three methods to implement.

public class CustomerAccount : IAccount
{ }

// This CustomerAccount class is labeled with : IAccount, which means that it will implement that interface.

In C#, an interface contains definitions for a group of related functionalities that a class can implement.

Interfaces are useful because they guarantee how a class behaves. This, along with the fact that a class can implement multiple interfaces, helps organize and modularize components of software.

It is best practice to start the name of an interface with “I”.

Interfaces

Lesson 1 of 2

1
Introduction to Interfaces
Since programming is complex, it’s easy to make mistakes. For example, maybe we try to use an int like a string. This would cause a type error. C# has rules built-in that check for those mistakes b…
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2
Build an Interface
For this lesson we will be designing a new set of transportation machines that satisfy the requirements of BOTH car designers and the highway patrol. First the highway patrol tells us: “Every autom…
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3
Implementing an Interface
Our interface is complete! Pretty easy, right? As we design our automobile-like classes, we’ll need to implement this IAutomobile interface. In C#, we must first clearly announce that a class impl…
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4
What Interfaces Cannot Do
The Sedan needs to satisfy more than the highway patrol’s rules (the IAutomobile interface). The car designers have asked that sedans are built and move in certain ways — it must have constru…
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5
Implementing an Interface Again
We’ve completed a Sedan class that satisfies both car designers and highway patrol: it can be constructed and change speed, and it implements the IAutomobile interface. But sedans aren’t the only…
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6
Finish Truck Class
The car designers have asked that trucks act a bit differently from sedans. Trucks need a new property called Weight. Whenever a truck is constructed, its number of wheels will depend on its weight…
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7
Testing Interfaces
Now we have a Sedan class and Truck class that implement the IAutomobile interface. Though they have some different behaviors, they both have the properties and method defined in the interface: * d…
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8
Review
Well done! In this lesson, you: * Learned that interfaces are useful to guarantee certain functionality across multiple classes * Built an interface using the interface keyword * Defined properties…
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