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What are interfaces and abstract classes?

Updated May 24, 2026

Short answer

Interfaces define contracts, while abstract classes provide partial implementations.

Deep explanation

Interfaces enforce consistent APIs across unrelated classes. Abstract classes allow shared logic and properties while preventing direct instantiation.

Real-world example

Payment gateways implement common interfaces for interchangeable integrations.

Common mistakes

  • Using inheritance where interfaces would provide better flexibility.

Follow-up questions

  • Can a class implement multiple interfaces?
  • Can abstract classes contain concrete methods?

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