Choose between a Java Interface and an Abstract Class
Role: Software Engineer
Category: Software Engineering Fundamentals
Difficulty: medium
Interview Round: Technical Screen
What is an abstract class in Java, what is an interface, and how would you choose between them? Explain the inheritance constraints and the kinds of implementation each can provide.
### What a Strong Answer Covers
Discuss instantiation, shared instance state, constructors, abstract and concrete behavior, and multiple interface implementation. Avoid treating an interface as a class or claiming that interfaces can never contain method bodies.
### Follow-up Questions
- When is composition a better choice than adding a shared superclass?
- How should a class resolve conflicting inherited interface defaults?
Overview: Compare Java interfaces and abstract classes through contracts, state, constructors, and inheritance limits. Use concrete design examples to choose between implementation inheritance and composition.