If a new requirement arises where an interface needs to add a method without breaking existing implementations, what is the best approach to handle this in a language that originally did not support default methods in interfaces?

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OOP & Design Patterns - Abstraction - Abstract Class vs Interface - When to Use Which

AAdd the method to the interface and require all implementers to update their code immediately.

BCreate a new interface that extends the original and adds the new method, then update clients to use the new interface.

CAdd the method as a static method in the interface.

DConvert the interface into an abstract class and provide a default implementation for the new method.

Step-by-Step Solution

Step 1: Understand backward compatibility
Adding a method directly to an interface breaks existing implementers if no default implementation exists.
Step 2: Why converting to abstract class is problematic
Changing interface to abstract class breaks existing multiple inheritance and design contracts.
Step 3: Using interface extension
Creating a new interface that extends the original preserves backward compatibility and allows gradual adoption.
Step 4: Static methods in interfaces
Static methods do not affect instance method contracts and cannot replace instance methods.
Final Answer:
Option B -> Option B
Quick Check:
Extending interfaces is the safe way to evolve contracts without breaking clients.

Quick Trick: Extend interfaces to add methods without breaking existing code.

Common Mistakes:

MISTAKES

Assuming all implementers can update immediately.
Thinking abstract classes can replace interfaces without impact.
Confusing static methods with instance methods in interfaces.

Trap Explanation:

PITFALL

Option A ignores backward compatibility; B changes design fundamentally; D misunderstands static method role.

Interviewer Note:

CONTEXT

Tests advanced understanding of interface evolution and backward compatibility strategies.

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If a new requirement arises where an interface needs to add a method without breaking existing implementations, what is the best approach to handle this in a language that originally did not support default methods in interfaces?

Step 1: Understand backward compatibility

Step 2: Why converting to abstract class is problematic

Step 3: Using interface extension

Step 4: Static methods in interfaces

Final Answer:

Quick Check:

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