Applying SOLID to real code in LLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Single Responsibility Principle (SRP) mean in real code?

SRP means each class or module should have only one reason to change. It should do one job well, like a chef focusing only on baking bread, not cooking the whole meal.

intermediate

Explain the Open/Closed Principle (OCP) with a simple example.

OCP means code should be open for extension but closed for modification. For example, adding new payment methods without changing existing payment code, like adding new toppings to a pizza without changing the base recipe.

intermediate

What is the Liskov Substitution Principle (LSP) in practice?

LSP means subclasses should work anywhere their parent class is expected without errors. Like replacing a car with a sports car that still drives the same way without surprises.

advanced

How does the Interface Segregation Principle (ISP) improve code design?

ISP says clients should not depend on interfaces they don't use. It’s like giving a remote control with only the buttons you need, not a giant one with confusing extras.

advanced

Describe the Dependency Inversion Principle (DIP) with a real-life analogy.

DIP means high-level modules should not depend on low-level modules directly. Instead, both depend on abstractions. Like using a universal plug adapter so your device works anywhere without changing the device itself.

Which SOLID principle suggests that a class should have only one reason to change?

A Single Responsibility Principle

B Open/Closed Principle

C Liskov Substitution Principle

D Dependency Inversion Principle

The Single Responsibility Principle states that a class should have only one reason to change.

What does the Open/Closed Principle encourage?

A Extending code without modifying existing code

B Modifying existing code frequently

C Using only abstract classes

D Avoiding inheritance

OCP encourages extending code behavior without changing existing code.

According to Liskov Substitution Principle, a subclass should:

A Change the behavior of the parent class

B Depend on concrete classes

C Work anywhere the parent class is expected

D Have fewer methods than the parent

LSP requires subclasses to be substitutable for their parent classes without errors.

Interface Segregation Principle advises to:

A Use one big interface for all clients

B Split interfaces so clients only use what they need

C Avoid interfaces altogether

D Make interfaces dependent on concrete classes

ISP suggests splitting interfaces to avoid forcing clients to depend on unused methods.

Dependency Inversion Principle promotes:

A No dependencies at all

B Low-level modules depend on high-level modules

C High-level modules depend on low-level modules

D Both depend on abstractions

DIP states both high-level and low-level modules should depend on abstractions.

Explain how you would apply the Single Responsibility Principle in a simple user management system.

Think about dividing tasks like storing user info and checking passwords.

Describe how the Dependency Inversion Principle helps in making code easier to test and maintain.

Consider how using interfaces allows replacing parts without breaking the whole system.