SOLID violations and fixes in LLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Single Responsibility Principle (SRP) state?

SRP means a class should have only one reason to change, meaning it should have only one job or responsibility.

intermediate

What is a common violation of the Open/Closed Principle (OCP)?

Changing existing code to add new features instead of extending it. This makes the system fragile and hard to maintain.

intermediate

How can the Liskov Substitution Principle (LSP) be violated?

When a subclass changes the expected behavior of the parent class, causing errors when used in place of the parent.

beginner

What does the Interface Segregation Principle (ISP) recommend?

Clients should not be forced to depend on interfaces they do not use. Use many small, specific interfaces instead of one large one.

intermediate

How does the Dependency Inversion Principle (DIP) improve design?

By depending on abstractions (interfaces) rather than concrete classes, making the system flexible and easier to change.

Which SOLID principle is violated if a class handles multiple unrelated tasks?

A Liskov Substitution Principle

B Open/Closed Principle

C Single Responsibility Principle

D Dependency Inversion Principle

A class with multiple unrelated tasks violates SRP because it has more than one reason to change.

What is a fix for violating the Open/Closed Principle?

A Extend classes using inheritance or composition

B Modify existing classes for new features

C Remove interfaces

D Use global variables

Extending classes allows adding new features without changing existing code, respecting OCP.

If a subclass breaks the behavior expected from its parent, which principle is violated?

A Interface Segregation Principle

B Liskov Substitution Principle

C Dependency Inversion Principle

D Single Responsibility Principle

LSP requires subclasses to be substitutable for their parents without altering expected behavior.

What does Interface Segregation Principle encourage?

A Many small, specific interfaces

B One large interface for all clients

C No interfaces at all

D Using abstract classes only

ISP encourages small, focused interfaces so clients only depend on what they use.

Dependency Inversion Principle suggests depending on:

A Concrete classes

B Static methods

C Global variables

D Abstractions (interfaces)

DIP promotes depending on abstractions to reduce coupling and increase flexibility.

Explain how you would fix a class that violates the Single Responsibility Principle.

Think about dividing jobs like splitting household chores among family members.

Describe how the Dependency Inversion Principle helps in making a system easier to maintain.

Imagine using a universal remote that works with many devices instead of a fixed one.