Abstract vs Interfaces in dotnet Framework

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Amit Mohanty · Answer

Abstract Classes: An abstract class is a class that cannot be instantiated on its own and may contain both abstract methods (without implementation) and non-abstract methods (with implementation). It is used when you want to provide a common base class with default behavior, while still forcing derived classes to override certain members. Key Characteristics: Can contain method implementations. Can have fields, constructors, access modifiers, and static members. Supports inheritance (single inheritance only). Allows both abstract and concrete methods. Useful when shared code is needed among derived classes. Interfaces: An interface defines a contract that classes must follow. It only contains method, property, event, or indexer declarations (in older versions of .NET; later versions allow default implementations). It is used when you want to define a contract that multiple unrelated classes can implement. Key Characteristics: Cannot contain fields or constructors (pre-C# 8.0). No implementation (pre-C# 8.0); only method signatures. Allows multiple inheritance. Promotes loose coupling and supports dependency injection patterns. Members are public by default and cannot have access modifiers When to Use Which? Use Abstract Class when: You need to provide default behavior. You want to share common implementation among related classes. Use Interface when: You need to define a contract that multiple unrelated classes can implement. You want to support multiple inheritance.

Vijay Kumari · Answer

Abstract Class Can have implemented methods, fields, and constructors. Supports inheritance (only one abstract/base class allowed). Used when classes share common behavior and implementation. Can have access modifiers. Interface Only contains method signatures (until C# 8, where default implementations are now allowed). Supports multiple inheritance (a class can implement multiple interfaces). Used when you want to define a contract without any implementation. All members are public by default.

Abstract vs Interfaces in dotnet Framework

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