C# Inheritance and Interfaces

10 Questions

What is the primary purpose of an interface?

To define a blueprint for other classes to follow

What is the difference between an abstract class and an interface?

Abstract classes have default implementations, interfaces do not

What is the purpose of the `Work()` method in the `IWorkable` interface?

To enforce subclasses to provide their own implementation

What is the relationship between the `Animal` class and the `IWorkable` interface?

The Animal class implements the IWorkable interface

What is the purpose of the `Employee` class?

To implement the IWorkable interface and define its own Work() method

What is the relationship between the `Dog` and `Cat` classes and the `Animal` class?

The Dog and Cat classes inherit from the Animal class

What is the purpose of an abstract class?

To provide a default implementation of a method

What is the difference between an interface and an abstract class?

An abstract class has default implementations, an interface does not

What is the purpose of the `IWorkable` interface?

To provide a way for classes to define their own Work() method

What is the relationship between the `Animal` class and its subclasses?

The Dog and Cat classes are subclasses of the Animal class

Study Notes

Inheritance in C#

Multiple Inheritance: the ability to inherit from more than one class, but it is a difficult concept and prohibited in C#.
Interface: an alternative to multiple inheritance, a collection of methods that can be used by any class as long as the class provides a definition to override the interface's abstract definitions.

Interfaces

C# supports single inheritance, but classes can implement any number of interfaces.
Classes can only inherit from a single class, abstract or non-abstract.
Interfaces are like classes that are totally abstract, all methods are abstract.
Abstract classes can have abstract and regular methods.
Classes implementing an interface agree to define details for all of the interface's methods.

Interface Syntax

The general form of an interface is [modifier] interface InterfaceIdentifier { ... }.
Members can be methods, properties, or events.
No implementation details are provided for any of the interface's members.

Interface Elements

Interfaces can only contain abstract methods, properties, indexers, and events.
Interface member access: all members are inherently public and abstract.
Interface inheritance: interfaces can inherit from other interfaces to create more complex ones for classes to implement.

Polymorphism

Interfaces provide polymorphism, many classes and structs may implement a particular interface.
Interfaces can be implemented either implicitly or explicitly.

Interface Example

An interface can be used to define a contract that must be implemented by any class or struct that implements it.
Example: public interface IDelete { void Delete(); } can be implemented by TextBox and Car classes.

Explicit Interfaces

Explicit interfaces require the user of the class to explicitly indicate that it wants to use the contract.
Note: explicit interfaces are not just a solution to namespace conflict problems.

Interfaces Multiple Inheritance

Classes and structs can inherit from multiple interfaces.
Interfaces can inherit from multiple interfaces.

Creating and Using Interfaces

In an abstract class, not all methods need to be abstract.
In an interface, all methods are abstract.

Interfaces vs. Abstract Classes

An interface is often used in place of an abstract class when there's no default implementation to inherit.
Like abstract classes, interfaces are typically public types, so they're normally declared in files by themselves with the same name as the interface and the .cs filename extension.

Understand the concept of inheritance in C#, including single inheritance and interfaces. Learn how classes can implement multiple interfaces.

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