What is the difference between abstract classes and interfaces in .NET?

What is the difference between abstract classes and interfaces in .NET?

In .NET, abstract classes and interfaces are two different ways to define the structure of a class. The main differences between them are:

1. Definition: Abstract classes can contain both abstract and non-abstract methods, properties, and fields, while interfaces can only contain method and property declarations.
2. Implementation: Abstract classes can provide default implementations for some methods, while interfaces cannot provide any implementation.
3. Inheritance: A class can inherit from only one abstract class, but can implement multiple interfaces.
4. Access Modifiers: Abstract classes can have access modifiers for their members, while interfaces can only have public members.

In general, abstract classes are used when we want to define a common base class with some default behavior, while interfaces are used when we want to define a contract that a class must follow without specifying any implementation details.