Important Differences Between Abstract class and Interface in C#

Abstract class in C#

An abstract class is a class that cannot be instantiated and is typically used as a base class for other classes. Abstract classes are used to provide a common interface for a group of related classes. They are defined using the “abstract” keyword in many programming languages such as Java, C#, Python and C++.

An abstract class can contain both abstract and concrete methods (methods with a body). Abstract methods are methods that do not have a body, and are meant to be overridden by subclasses. Concrete methods are methods that have a body and can be called on an instance of the class.

Abstract classes are useful when there is a common functionality that needs to be shared among several related classes. For example, a class representing a shape may be defined as an abstract class and contain methods for calculating the area and perimeter of the shape. Specific shapes such as a circle and a rectangle can then be defined as subclasses of the abstract shape class and provide their own implementation of the abstract methods.

It is important to note that an abstract class cannot be instantiated, but can be subclassed. Also, a class can only be subclassed if all the abstract methods have been implemented by the subclass.

In conclusion, an abstract class is a class that can’t be instantiated, it is used as a blueprint for other classes, it’s used to define a common interface for a group of related classes, and it’s useful when there is a common functionality that needs to be shared among several related classes.

Interface in C#

In C#, an interface is a contract that defines a set of methods, properties, and events that a class or struct must implement. Interfaces are defined using the “interface” keyword and contain only the signatures of the members (methods, properties, and events) without any implementation.

Interfaces are useful for creating flexible and extensible code, as they allow for classes to implement multiple interfaces and provide their own implementation of the members defined in the interfaces.

For example, a class called “Car” can implement an interface called “IDrivable” that defines methods such as Start(), Stop() and Accelerate(). The Car class can then provide its own implementation of these methods.

Interfaces can also be used to define events and properties. For example, an interface called “ISetVolume” might define an event called “VolumeChanged” and a property called “Volume”.

In C#, a class can implement multiple interfaces, and an interface can inherit from one or more other interfaces using the “:” operator. It is also possible to define explicit interface implementation, which allows a class to implement multiple interfaces that have members with the same name.

In addition to classes and structs, C# 8.0 introduced the concept of interface implementation for records and pattern matching for interfaces.

Important Difference Between Abstract class and Interface in C#

In C#, there are a few important differences between an abstract class and an interface:

1. Implementation: An abstract class can provide both an implementation of methods and an abstract method, while an interface can only provide a method signature and no implementation.
2. Inheritance: A class can inherit from only one abstract class, but it can implement multiple interfaces.
3. Access modifiers: Members of an abstract class can have access modifiers such as public, protected and private, whereas members of an interface are public by default.
4. Constructors: An abstract class can have constructors and a destructor, while an interface can’t have any constructors or destructors.
5. Properties: An abstract class can have properties with or without implementation, while an interface can only have properties without an implementation.
6. Use case: Abstract classes are useful when there is a common functionality that needs to be shared among several related classes and when a class is being defined as a base class, while interfaces are useful when a class needs to implement multiple behavior, and when a class needs to implement multiple behavior or functionality.
7. Constant, readonly and static fields: Abstract classes can have constant, readonly, and static fields, while interfaces can’t have any fields.
8. Default implementation: Interface don’t allow default implementation of methods, but abstract class can have default implementation of methods.