OBJECT DESIGN · LLD · MEDIUM CODEX

Object Design · LLD Interview Questions — Medium

Q: What is the difference between class cohesion and method cohesion in system design?

- Class Cohesion: The degree to which the fields and methods of a single class belong together logically. High class cohesion means all members are focused on a single responsibility. - Method Cohesio

Q: What is the difference between syntactic coupling and semantic coupling?

- Syntactic Coupling: The caller depends on the names, signatures, and types of the called class (easily checked by compiler). - Semantic Coupling: The caller depends on the internal behavior, state t

Q: What are the key indicators (code smells) that signal a need for LLD refactoring?

- Indicators: - Divergent Change: A single class must be modified in different ways to support unrelated new requirements. - Shotgun Surgery: A single change requires making tiny edits across dozens o

Q: What is the "Feature Envy" code smell, and how do you resolve it?

- Feature Envy: A class method is more interested in the data of another class than its own class's data. - Resolution: Apply the Move Method refactoring technique. Relocate the envious method into th

Q: What is the "Long Method" code smell, and what LLD techniques reduce it?

- Long Method: A method that contains too many lines of code, making it hard to read, maintain, and unit test. - LLD Techniques: - Extract Method: Split logical sections of the method into smaller, de

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Q1What is the difference between class cohesion and method cohesion in system design?

Class Cohesion: The degree to which the fields and methods of a single class belong together logically. High class cohesion means all members are focused on a single responsibility.
Method Cohesion: The level of focus of a single method. High method cohesion means the method performs exactly one distinct operation (does not mix formatting, validation, and calculations).

Q2What is the difference between syntactic coupling and semantic coupling?

Syntactic Coupling: The caller depends on the names, signatures, and types of the called class (easily checked by compiler).
Semantic Coupling: The caller depends on the internal behavior, state transitions, or execution order of the called class (harder to detect, causes fragile execution bugs when implementation changes).

Q3What are the key indicators (code smells) that signal a need for LLD refactoring?

Indicators:
- Divergent Change: A single class must be modified in different ways to support unrelated new requirements.
- Shotgun Surgery: A single change requires making tiny edits across dozens of different classes.
- Feature Envy: A method inside Class A constantly reads/writes variables of Class B instead of its own.

Q4What is the "Feature Envy" code smell, and how do you resolve it?

Feature Envy: A class method is more interested in the data of another class than its own class's data.
Resolution: Apply the Move Method refactoring technique. Relocate the envious method into the class whose data it is accessing, or pass the necessary data as parameters to keep logic localized.

Q5What is the "Long Method" code smell, and what LLD techniques reduce it?

Long Method: A method that contains too many lines of code, making it hard to read, maintain, and unit test.
LLD Techniques:
- Extract Method: Split logical sections of the method into smaller, descriptive helper functions.
- Replace Temp with Query: Replace temporary local variables with direct query methods to simplify the signature.

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