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Key Differences between Abstract Classes and Interfaces in C#

In C#, abstract classes and interfaces are used to achieve abstraction and define contracts that classes must follow. Here are the key differences:

1. Definition: An abstract class can contain both abstract and non-abstract members, while an interface can only contain method signatures and properties.
2. Inheritance: A class can inherit from only one abstract class using the 'inheritance' keyword, but it can implement multiple interfaces using the 'implements' keyword.
3. Implementation: Abstract classes can provide default implementations for methods, but interfaces cannot have method implementations.
4. Access Modifiers: Abstract classes can have access modifiers for their members, whereas interfaces cannot specify access modifiers for their members.
5. Usage: Use abstract classes when you want to provide a common implementation for a group of related classes. Use interfaces when you want to define a contract that multiple unrelated classes can implement.

Understanding these differences is crucial for .Net developers when designing and implementing software components in C#.

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