Types of Classes in C# (2024)

As it is known C# is an object-oriented programming language that provides us the ability to reuse existing code. Classes are fundamental parts of object-oriented programming language. A class is a blueprint for creating an object- a particular data structure that includes both data (often known as attributes or properties) and code (functions or methods) that operate on that data. Objects are instances of classes, and a class defines the common behavior and structure that its objects share. Some important key points regarding classes in C# are given below.

• Classes are reference types that hold the object created dynamically in a heap.
• System.Object is the base type for all the classes.
• If we do not declare the access modifier for a class, then by default it is internal.
• If we do not declare the access modifier for the methods and variables in a class, then by default it is private.
• Directly inside the namespaces, declarations of private classes are not allowed

In his article, we will explain the types of classes in C#.

Types of Classes in C#

There are four types of classes in C#.

1. Abstract Class
2. Partial Class
3. Sealed Class
4. Static Class

Abstract Class:

An abstract class is a class that provides the definition for its subclasses. An abstract class can not be instantiated. An abstract class is used to provide a base for child classes to extend and implement abstract methods and override or use the implemented methods in the abstract class. Some key points regarding abstract class are mentioned below.

• An object can not be created from the abstract class.
• We use abstract keyword to declare an abstract class.
• To use the abstract class, it must be inherited by a subclass.
• An Abstract class contains both abstract and non-abstract methods.
• The methods inside the abstract class can either have an or no implementation.
• We can inherit two abstract classes; in this case, implementation of the base class method is optional.
• An Abstract class has only one subclass.
• Methods inside the abstract class cannot be private.
• If there is at least one method abstract in a class, then the class must be abstract.

Example:

abstract class AbstractClass
{
}

Partial Class:

A partial class is used to divide properties, methods, and events into multiple partial classes that are joined in a single class at compile time. A partial class is useful when the class definition is too large or you are working on a complex model or feature and you want to divide the responsibility of implementation into more than one developer. Some key points regarding partial class are mentioned below.

• All the parts of the partial class must be prefixed with the partial keyword.
• If you seal a specific part of a partial class, the entire class is sealed, the same as for an abstract class.
• Inheritance cannot be applied to partial classes.
• The classes written in two class files are combined at run time.

Example:

partial class PartialClass
{
}

Sealed Class:

A sealed class is a class that can not be inherited. In C#, sealed classes are used to prevent inheritance from other classes. This helps to prevent security issues. For example, the methods in a sealed class cannot be manipulated from other classes. Some key points regarding sealed classes are mentioned below.

• A Sealed class is created using the sealed keyword.
• Access modifiers are not applied to a sealed class.
• To access the sealed members, we must create an object of the class.
• When casting objects, the runtime must check the type of the object at runtime. When casting to a sealed type, the runtime must only check the type of the object, so it is faster.
• Sealed classes are best used when you have a class with static members, such as the “Pens” And “Brushes” classes of the System.

Example:

sealed class SealedClass
{
}

Static Class:

Static classes are the classes that can not be instantiated, this means you can create an object (instance) of a static type class using the new keyword. You can directly call static class members using their names. Some key points regarding static class are mentioned below.

• It was created using the static keyword.
• Only static members are allowed; in other words, everything inside the class must be static.
• We cannot create an object of the static class.
• Static classes are sealed and therefore cannot be inherited. They are also not available for use in the same way as a regular class.
• It allows only a static constructor to be declared.
• The static class methods can be called using the class name without creating the instance.
• Static classes are a good choice when you only need a utility class that contains several utility methods. For example, the methods of the Math class in the System namespace are organized in a static class.
• Static classes can be used to write your own instance wrapper around the file system API.
• Static classes are used to create data and functions that can be accessed without creating an instance of the class.
• Static classes consume fewer resources.

Example:

static class StaticClass
{
}