[Solved] Suppose you have a legacy system that violates the Open/Closed Principle by frequently... What is the best strategy to refactor it to comply with OCP without breaking existing functionality? | OOP & Design Patterns

OOP & Design Patterns - Open/Closed Principle - Open for Extension, Closed for Modification

Suppose you have a legacy system that violates the Open/Closed Principle by frequently modifying core classes for new features. What is the best strategy to refactor it to comply with OCP without breaking existing functionality?

AReplace all core classes with interfaces and rewrite all implementations from scratch

BUse global variables to control behavior changes instead of modifying classes

CContinue modifying core classes but add feature flags to isolate changes

DIntroduce abstract base classes or interfaces and create new subclasses for new features, leaving existing classes unchanged

Step-by-Step Solution

Step 1: Understand refactoring goals
Refactor to enable extension via new subclasses without modifying existing tested classes.
Step 2: Why introducing abstract base classes or interfaces and creating new subclasses for new features, leaving existing classes unchanged fits
Introducing abstractions and subclassing allows adding features by extension, preserving existing code.
Step 3: Why other options fail
Replace all core classes with interfaces and rewrite all implementations from scratch is costly and risky; Continue modifying core classes but add feature flags to isolate changes continues violating OCP; Use global variables to control behavior changes instead of modifying classes introduces global state, increasing complexity and bugs.
Final Answer:
Option D -> Option D
Quick Check:
Refactor by abstraction and extension, not rewrite or global state hacks.

Quick Trick: Refactor with abstractions and subclasses, keep existing code intact [OK]

Common Mistakes:

MISTAKES

Thinking rewrite is the only way to comply with OCP
Believing feature flags solve OCP violations
Using global variables as a workaround

Trap Explanation:

PITFALL

Option A is impractical; C and D ignore OCP principles; B aligns with best refactoring practices.

Interviewer Note:

CONTEXT

Evaluates candidate's ability to apply OCP in legacy code refactoring scenarios.

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Solution Trace

More OOP & Design Patterns Quizzes

What is the best strategy to refactor it to comply with OCP without breaking existing functionality?

Step 1: Understand refactoring goals

Step 2: Why introducing abstract base classes or interfaces and creating new subclasses for new features, leaving existing classes unchanged fits

Step 3: Why other options fail

Final Answer:

Quick Check:

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