All 17 Interfaces & Abstract Classes questions
More in Interfaces & Abstract Classes
Why program to an interface rather than a concrete type? What is an interface, and what can (and can't) it contain in its most basic form? What is an abstract class, and how does it differ from a fully concrete base class? What is the difference between an interface and an abstract class in C#, and when should you choose one over the other? What are default interface methods and when are they useful? Can a class implement two interfaces with the same method? How is it resolved? How do you decide between using an interface versus an abstract class for a given design? How do default interface methods (C# 8+) let an interface provide implementation, and what backward-compatibility problem do they solve? How does explicit interface implementation work, and when would you use it instead of a normal (implicit) implementation? When would you choose an abstract class over an interface for extensibility?
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C# › Interfaces & Abstract Classes

What is the difference between an interface and an abstract class?

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Answer

An abstract class can hold state and shared implementation and supports single inheritance; an interface is a contract a type can implement many of. Use interfaces for capabilities, abstract classes for a shared base.
public interface IPayable { decimal Pay(); }
public abstract class Employee : IPayable { public string Name=""; public abstract decimal Pay(); }
Real-world example IPayable expresses the capability; Employee shares Name across subtypes.
All 17 Interfaces & Abstract Classes questions