{"id":419,"date":"2022-01-06T17:08:45","date_gmt":"2022-01-06T10:08:45","guid":{"rendered":"https:\/\/csharptutorial.net\/?page_id=419"},"modified":"2022-06-03T15:04:35","modified_gmt":"2022-06-03T08:04:35","slug":"csharp-abstract-class","status":"publish","type":"page","link":"https:\/\/www.csharptutorial.net\/csharp-tutorial\/csharp-abstract-class\/","title":{"rendered":"C# Abstract Class"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn about C# abstract classes and how to use them effectively.<\/p>\n\n\n\n

Introduction to C# abstract classes<\/h2>\n\n\n\n

An abstract class is a class<\/a> declared with the abstract<\/code> keyword like this:<\/p>\n\n\n

abstract<\/span> class<\/span> MyClass<\/span>\n{\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Unlike a regular class, you cannot create any instances of an abstract class. Typically, you define an abstract class for subclassing by other classes.<\/p>\n\n\n\n
Abstract methods<\/h3>\n\n\n\n
To define an abstract method, you use the abstract<\/code> keyword. Unlike a regular method, an abstract method doesn’t have an implementation. <\/p>\n\n\n\n
When you subclass an abstract class that has an abstract method, you need to implement the abstract method in the subclass.<\/p>\n\n\n\n
The following example shows an example of an abstract method:<\/p>\n\n\n
abstract<\/span> class<\/span> MyClass<\/span>\n{\n    public<\/span> abstract<\/span> string<\/span> AbstractMethod<\/span>(<\/span>)<\/span>;\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
If a class contains at least one abstract method, it must be an abstract class.<\/p>\n\n\n\n
Abstract properties<\/h3>\n\n\n\n
Like an abstract method, an abstract property consists of the abstract<\/code> keyword and provides no implementation for the get<\/code> or set<\/code> access modifier.<\/p>\n\n\n
abstract<\/span> class<\/span> MyClass<\/span>\n{\n    public<\/span> abstract<\/span> string<\/span> AbstractProperty { get<\/span>; set<\/span>; }\n    public<\/span> abstract<\/span> string<\/span> AbstractMethod<\/span>(<\/span>)<\/span>;    \n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
C# abstract class example<\/h2>\n\n\n\n
First, define an abstract class called Shape<\/code>:<\/p>\n\n\n
abstract<\/span> class<\/span> Shape<\/span>\n{\n    public<\/span> abstract<\/span> double<\/span> Area<\/span>(<\/span>)<\/span>;\n\n    public<\/span> abstract<\/span> int<\/span> Side { get<\/span>; }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
The Shape<\/code> class has an abstract method Area()<\/code> that returns the area of the shape. It also has the abstract property Side<\/code> that returns the number of sides of the shape.<\/p>\n\n\n\n
Second, define the Circle<\/code> class that inherits from the Shape<\/code> class:<\/p>\n\n\n
class<\/span> Circle<\/span> : Shape<\/span>\n{\n    public<\/span> double<\/span> Radius { get<\/span>; set<\/span>; }\n\n    public<\/span> override<\/span> int<\/span> Side => 0<\/span>;\n\n    public<\/span> Circle<\/span>(double<\/span> radius<\/span>)<\/span>\n    {\n        Radius = radius;\n    }\n\n    public<\/span> override<\/span> double<\/span> Area<\/span>(<\/span>)<\/span>\n    {\n        return<\/span> Math.PI * Radius * Radius;\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
In this Circle<\/code> class, we must implement both Area()<\/code> method and Side<\/code> property. <\/p>\n\n\n\n
Since a circle has zero sides, the Side<\/code> property returns 0. Also, the Area()<\/code> method returns the area of the circle based on its radius (R) and PI using the formula PI * R2<\/sup><\/p>\n\n\n\n
Third, define the Square<\/code> class that inherits from the Shape<\/code> class:<\/p>\n\n\n
class<\/span> Square<\/span>: Shape<\/span>\n{\n    public<\/span> double<\/span> Length { get<\/span>; set<\/span>; }\n\n    public<\/span> override<\/span> int<\/span> Side => 4<\/span>;\n\n    public<\/span> Square<\/span>(double<\/span> length<\/span>)<\/span>\n    {\n        Length = length;\n    }\n    public<\/span> override<\/span> double<\/span> Area<\/span>(<\/span>)<\/span>\n    {\n        return<\/span> Length * Length;\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
In this Square<\/code> class, the Side<\/code> property returns 4. Also, the Area()<\/code> method returns the area of the square based on its length.<\/p>\n\n\n\n
\/\/ Program.cs<\/span>\n\nShape[] shapes =\n{\n    new<\/span> Square(10<\/span>),\n    new<\/span> Circle(100<\/span>)\n};\n\nforeach<\/span>(Shape shape in<\/span> shapes)\n{\n    Console.WriteLine($\"The area of the {shape}<\/span> is {shape.Area():0.<\/span>##}<\/span>\"<\/span>);\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
The area of the Square is<\/span> 100<\/span>\nThe area of the Circle is<\/span> 31415.93<\/span><\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary<\/h2>\n\n\n\n
  • An abstract class cannot be instantiated. It can be subclassed.<\/li>
  • An abstract class may contain abstract members including abstract methods and properties.<\/li>
  • Abstract methods and properties do not contain implementation.<\/li>
  • The subclasses of an abstract class must implement the abstract methods and properties.<\/li><\/ul>\n
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Finally, create an array<\/a> of shapes including a circle and a square, and calculate their areas:<\/p>\n\n\n
Note that an abstract method cannot be private<\/a>. In other words, its accessibility level needs to be either public or protected.<\/p>\n\n\n\n
An abstract class may contain abstract members such as abstract methods and properties<\/a>. <\/p>\n\n\n\n