What is the difference between an interface and an abstract class?
PICTURE THIS: RAG CHATBOT
Simple meaning
An interface is a contract of members a type must implement
WHY — C# instead of guessing?
Why interviewers care about C#:
contrast on C#, not two memorised paragraphs.
the developer, then one case where picking wrong hurts.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1An interface is a
contract of members a type must implement
- 2Why it exists
a class can implement many.
- 3An abstract class can
hold fields and shared code, and a class can inherit only one.
- 4I pick an interface
for capability, and an abstract base when implementations truly share state.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
An interface is a contract of members a type must implement a class can implement many.