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Top 14 SOLID Principles Interview Questions and Answers

31/Aug/2024 | 10 minutes to read

design

Here is a List of essential SOLID Principles Interview Questions and Answers for Freshers and mid level of Experienced Professionals. All answers for these SOLID Principles questions are explained in a simple and easiest way. These basic, advanced and latest SOLID Principles questions will help you to clear your next Job interview.

SOLID Principles Interview Questions and Answers

These questions are targeted for Object-Oriented Design Principles like SOLID Principles, DRY, SoC, KISS etc. C# Programming language is used to show examples.

1. What are the SOLID Principles?

SOLID Principles is an acronym of 5 principles in Object Oriented Design (OOD). Robert C. Martin introduced these 5 principles in his 2000 paper "Design Principles and Design Patterns".

  • S - Single Responsibility Principle
  • O - Open Closed Principle
  • L - Liskov Substitution Principle
  • I - Interface Segregation Principle
  • D - Dependency Inversion Principle

1. Describe the Single Responsibility Principle (SRP).

In Object Oriented Programming, Single Responsibility (SRP) ensures that every module or class should be responsible for single functionality supported by the software system. In other words, Every class should have one and only reason to change it.
For example, In ASP.NET MVC HomeController class should be responsible related to Home Page functionality of software system.
Another example, consider a class that handles user authentication and also manages database operations. If a change is required in the authentication logic, the class would need to be modified, potentially affecting the database operations as well. By separating these responsibilities into two different classes, one for authentication and another for database operations, the SRP is upheld, and the classes become more maintainable and testable.

3. Describe the Open Close Principle (OCP).

Open Close Principle (OCP) states or ensures that A class, component or entity should be open for extension but close for modification. In detail, We can extend any class via Interface, Inheritance or Composition whenever it's required instead of opening a class and modifying it's code.
For example, suppose you have implemented a functionality to calculate area of Rectangle and after some time you need to calculate the area of Square, then In this case you should not modify your original class code to add extra code for square. Instead you should create one base class initially and now you should extend this base class by your square class.
This principle promotes code extensibility by allowing new features to be added without modifying the existing codebase, reducing the risk of introducing bugs and making the code more maintainable.

4. Explain Liskov Substitution Principle (LSP).

Liskov Substitution Principle (LSP) states that Objects in a program can be replaced by the instances of their subtypes without modifying the correctness of a program.
In other words, if A is subtype of B then instances of B may be replaced by the instances of A without altering the program correctness.
For example, consider a base class Vehicle with a method startEngine(). If you have a subclass ElectricCar that extends Vehicle, the startEngine() method in ElectricCar should behave in a way that is compatible with the base class implementation, even if the implementation details differ (e.g., starting an electric motor instead of a combustion engine).

5. Explain Interface Segregation Principle (ISP).

Interface Segregation Principle (ISP) states that use many client specific interfaces instead of one general purpose interface.
In other words No client should be forced to implement other methods which it does not require. It means it's better to create a separate interface and allow your classes to implement multiple interfaces.
This principle helps to reduce coupling between components and promotes code reusability. For example, instead of having a single VehicleInterface with methods for starting an engine, opening doors, and adjusting the air conditioning, you could have separate interfaces for EngineOperations, DoorOperations, and ClimateControl. This way, a client that only needs to start an engine would not be coupled to the unnecessary methods for door operations or climate control.

6. How does the Dependency Inversion Principle (DIP) promote code flexibility and testability?

The Dependency Inversion Principle (DIP) suggests that higher-level components should not directly depend on lower-level components; instead, both should depend on abstractions. This principle promotes decoupling and modularity in software design. Consider a real-world example of an e-commerce application that needs to handle different payment gateways (e.g., PayPal, Stripe, etc.). Instead of having the application's core logic directly depend on specific payment gateway implementations, you can introduce an abstraction layer in the form of an interface or an abstract class, let's call it PaymentGateway.
Both the application's core logic and the concrete payment gateway implementations (e.g., PayPalGateway, StripeGateway) would then depend on this PaymentGateway abstraction. This way, the application can work with any payment gateway implementation that adheres to the PaymentGateway interface, without needing to modify its core logic.
By following the DIP, you gain several advantages:
  • Loose Coupling: The application's core logic is decoupled from the specific payment gateway implementations, making it easier to maintain and extend the codebase.
  • Testability: Since the application depends on an abstraction, you can easily create mock or stub implementations of the PaymentGateway interface for unit testing purposes.
  • Extensibility: Adding a new payment gateway implementation becomes straightforward, as you only need to create a new class that implements the PaymentGateway interface, without modifying the application's core logic.
  • Maintainability: Changes to the payment gateway implementations do not affect the application's core logic, as long as they adhere to the PaymentGateway interface contract.

12. How Design Principles are different from Design Patterns?

  • Design Principles are the core principles which we are supposed to follow while designing any software system on any platform using any programming language. Examples of Design Principles:
    • Dependency on abstraction not concrete classes
    • Encapsulate that varies
    • Program to interfaces not implementations
  • Design Patterns are the solutions to common occurring general problems, they are not exact program that can be fit to solve your problem rather you need to customize according to your problem. Design Patterns are already invented solutions which are well tested and safe to use. Examples of Design Patterns:
    • Single Design Pattern: When you want only one instance of a class.
    • Repository Design Pattern: To separate different layers of application (Business Repository, Data Repository)

7. What is Inversion of Control (IoC)?

Some Other Design Principles Interview Questions

8. What is 'Don't repeat yourself (DRY)' Principle?

DRY or 'Don't repeat yourself' is a software design principle that emphasizes on how to avoid the duplicate code in your codebase. and replace that redundant code with some less changing components like Abstraction . A redundant code creates problems like
  • You might have multiple files to apply similar code changes so it's time consuming.
  • Code readability is a big problem.
So the DRY principle helps you to solve these types of problems and allows you to write reusable, efficient code that provides better readability and maintainability. For more refer DRY Principle.

9. Explain the Separation of Concerns (SoC) design principle.

10. Explain KISS design principle.

KISS stands for "Keep It Simple, Stupid" means keep your logic simple that will be easy to maintain, and anyone can understand in future. Primary goal is simplicity of your code.

11. How Encapsulation works as a design Principle?

12. What is YAGNI Principle?

YAGINI principle states that "You Aren't Gonna Need It" means implement the functionality that you really need, not the functionality you think that "Just in some case we need them" or you should not implement the functionality that you are just presuming in future software needs. For more visit Yagni by Martin Fowler.

13. Good Understanding of SOLID Principles

It's a YouTube video explaining about SOLID Principles and Dependency Injection.

Some General Interview Questions for SOLID Principles

1. How much will you rate yourself in SOLID Principles?

When you attend an interview, Interviewer may ask you to rate yourself in a specific Technology like SOLID Principles, So It's depend on your knowledge and work experience in SOLID Principles. The interviewer expects a realistic self-evaluation aligned with your qualifications.

2. What challenges did you face while working on SOLID Principles?

The challenges faced while working on SOLID Principles projects are highly dependent on one's specific work experience and the technology involved. You should explain any relevant challenges you encountered related to SOLID Principles during your previous projects.

3. What was your role in the last Project related to SOLID Principles?

This question is commonly asked in interviews to understand your specific responsibilities and the functionalities you implemented using SOLID Principles in your previous projects. Your answer should highlight your role, the tasks you were assigned, and the SOLID Principles features or techniques you utilized to accomplish those tasks.

4. How much experience do you have in SOLID Principles?

Here you can tell about your overall work experience on SOLID Principles.

Conclusion

We have covered some frequently asked SOLID Principles Interview Questions and Answers to help you for your Interview. All these Essential SOLID Principles Interview Questions are targeted for mid level of experienced Professionals and freshers.
While attending any SOLID Principles Interview if you face any difficulty to answer any question please write to us at info@qfles.com. Our IT Expert team will find the best answer and will update on the portal. In case we find any new SOLID Principles questions, we will update the same here.