Object-oriented design principles in LLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Single Responsibility Principle (SRP)?

SRP means a class should have only one reason to change. It should do one job only, like a chef who only cooks and doesn't clean.

intermediate

Explain the Open/Closed Principle (OCP).

OCP says software entities should be open for extension but closed for modification. Think of a phone case that fits new phones without changing the phone itself.

intermediate

What does the Liskov Substitution Principle (LSP) ensure?

LSP means subclasses should work anywhere their parent class works without breaking things. Like replacing a car tire with a new one that fits perfectly.

advanced

Describe the Interface Segregation Principle (ISP).

ISP says clients should not depend on interfaces they do not use. It's like having separate menus for drinks and food, so you only see what you want.

advanced

What is the Dependency Inversion Principle (DIP)?

DIP means high-level modules should not depend on low-level modules. Both should depend on abstractions. Like using a universal remote that works with many devices.

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

A Open/Closed Principle

B Single Responsibility Principle

C Liskov Substitution Principle

D Dependency Inversion Principle

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

What does the Open/Closed Principle encourage?

A Classes should be open for modification

B Classes should be closed for extension

C Classes should be open for extension but closed for modification

D Classes should have multiple responsibilities

OCP means classes can be extended without changing existing code.

Liskov Substitution Principle ensures that:

A Subclasses can replace their parent classes without errors

B Classes should have only one responsibility

C Interfaces should be large and general

D High-level modules depend on low-level modules

LSP means subclasses should work anywhere their parent class works.

Interface Segregation Principle advises to:

A Use one big interface for all clients

B Avoid using interfaces

C Depend on concrete classes

D Split interfaces so clients only use what they need

ISP means clients should not depend on interfaces they do not use.

Dependency Inversion Principle promotes:

A Both depend on abstractions

B Low-level modules depend on high-level modules

C High-level modules depend on low-level modules

D No dependencies at all

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

Explain the five main object-oriented design principles and give a simple real-life example for each.

Think about everyday objects or situations that show each principle.

How do object-oriented design principles help in building scalable and maintainable software?

Consider how good design makes life easier for developers.