OOP & Design Patterns - Abstraction - Abstract Class vs Interface - When to Use Which
A candidate claims that interfaces can contain instance variables to hold state, just like abstract classes. What is the flaw in this statement?
A candidate claims that interfaces can contain instance variables to hold state, just like abstract classes. What is the flaw in this statement?
medium🐞 Bug Identification Q7 of Q15
Step-by-Step Solution
Solution:
Step 1: Recall interface variable rules
Interfaces can declare only static final (constant) variables, no instance variables.Step 2: Compare with abstract classes
Abstract classes can have instance variables to hold state.Step 3: Identify flaw
Candidate incorrectly assumes interfaces can hold instance state, which is not allowed.Final Answer:
Option D -> Option DQuick Check:
Interfaces only allow static final variables, no instance state [OK]
Quick Trick: Interfaces cannot hold instance state, only constants [OK]
Common Mistakes:
MISTAKES- Confusing static final with instance variables
- Assuming interfaces behave like classes in state management
- Believing private variables are allowed in interfaces
Trap Explanation:
PITFALL- Candidates conflate interface constants with instance variables, missing key language restrictions.
Interviewer Note:
CONTEXT- Tests knowledge of interface variable constraints and state management.
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