20 SOLID Design Principles Interview Questions and Answers

If you’re interviewing for a position in software development, you’re likely to be asked about your understanding of the SOLID Design Principles. These principles are a set of guidelines that developers can use to create software that is easy to maintain and extend. Demonstrating your knowledge of these principles can show the interviewer that you have the skills and experience to be a successful software developer. In this article, we review some common questions about the SOLID Design Principles and how you should answer them.

SOLID Design Principles Interview Questions and Answers

Here are 20 commonly asked SOLID Design Principles interview questions and answers to prepare you for your interview:

1. Can you explain the SOLID design principles?

The SOLID design principles are a set of guidelines that aim to help developers create more robust and maintainable software. The acronym stands for Single responsibility, Open-closed, Liskov substitution, Interface segregation, and Dependency inversion.

Single responsibility means that each class or module should have a single, well-defined purpose. Open-closed means that code should be open for extension but closed for modification. Liskov substitution means that subclasses should be able to be used in place of their parent class without breaking the code. Interface segregation means that interfaces should be small and focused, and that no client should be forced to depend on methods it does not use. Dependency inversion means that code should depend on abstractions, not concrete implementations.

2. What do you understand about coupling and cohesion in software development?

Coupling is the degree to which one software component is dependent on another. The more coupling there is between two components, the more difficult it is to make changes to one without affecting the other. Cohesion, on the other hand, is the degree to which a software component is self-contained. A component with high cohesion is one that is focused on a single task and is not tightly coupled to other components.

3. How do you reduce coupling and increase cohesion in your code?

One way to reduce coupling is to use dependency injection, which allows you to inject dependencies into a class rather than having the class create them itself. This way, the class is not tied to a specific implementation of the dependency. To increase cohesion, you can make sure that each class has a single responsibility, and that its methods are all related to that responsibility.

4. What is a singleton class? When should it be used?

A singleton class is a class that can only be instantiated once. This is usually accomplished by making the constructor private and providing a static method that returns the only instance of the class. Singletons are often used for managing resources that are limited in number, such as database connections.

5. What are some of the most common anti-patterns that you have observed when working on large projects?

One of the most common anti-patterns I have observed is code that is needlessly complex and difficult to understand. This can happen when developers try to over-engineer solutions or when they fail to properly comment their code. Another common anti-pattern is code that is duplicated throughout the codebase. This can happen when developers are not aware of existing functionality or when they are trying to create shortcuts for themselves.

6. What are some best practices for avoiding duplicate code?

One best practice for avoiding duplicate code is to create abstract base classes that define the common functionality shared by the child classes. Another best practice is to use interfaces to define the contracts that must be implemented by the child classes. Finally, it is also helpful to use design patterns to promote code reuse.

7. What do you think is the biggest misconception people have about software engineering, or at least one thing they get wrong?

I think the biggest misconception people have about software engineering is that it is all about code. In reality, software engineering is about much more than just code. It is about designing systems and solving problems. It is about understanding how people use and interact with systems. It is about communication and collaboration. And, yes, it is about code. But code is just one part of the software engineering puzzle.

8. Why is tight coupling bad?

Tight coupling is when two classes are too closely linked together, and changes to one class can unintentionally break the other class. This can lead to code that is difficult to maintain and debug.

9. What are some ways to avoid using multiple inheritance in programming?

There are a few ways to avoid using multiple inheritance in programming. One way is to use interfaces instead of classes to define the functionality that a class should have. Another way is to use composition instead of inheritance, so that a class contains other classes instead of inheriting from them. Finally, you can use delegation, where one class delegates responsibility for certain tasks to another class.

10. Do you prefer loose or tight coupling in your programs? Why?

I prefer loose coupling in my programs because it allows for more flexibility and easier maintenance. If two components are tightly coupled, then a change in one component can potentially break the other component. With loose coupling, the components are more independent and can be changed without affecting the other components.

11. What is the difference between object oriented programming and procedural programming?

Object oriented programming is a programming paradigm that is based on the concept of objects. These objects are self-contained and can interact with each other. Procedural programming, on the other hand, is a programming paradigm that is based on the concept of procedures. These procedures are a series of steps that are followed in order to complete a task.

12. Which language features help ensure that the SOLID design principles are followed during development?

Some of the language features that help ensure that the SOLID design principles are followed during development include:

– Encapsulation: This ensures that the internals of a class are hidden from the outside world, and that only the public interface is exposed. This helps to prevent code from being changed in a way that could break existing code that depends on it.

– Inheritance: This allows for code reuse, and also helps to ensure that subclasses maintain the same interface as their parent class. This helps to prevent code from being changed in a way that could break existing code that depends on it.

– Polymorphism: This allows for code to be written in a way that is more flexible and extensible. This helps to prevent code from being changed in a way that could break existing code that depends on it.

13. What are some cases where high cohesion can be seen as negative?

High cohesion can be seen as negative when it leads to code that is tightly coupled and difficult to change. This can happen when a class or module is trying to do too many things, and as a result, the code is difficult to understand and maintain.

14. Can you give me an example of how low coupling and high cohesion work together?

Low coupling means that each component of a system is independent from the others, while high cohesion means that the components are all working together towards a common goal. An example of how these two concepts work together would be a system where each component is responsible for a specific task, and they all work together to complete a larger task. This would be considered to be a system with low coupling and high cohesion.

15. What is OCP (Open/Closed Principle) and why is it important?

OCP is the Open/Closed Principle, which states that software entities (classes, modules, functions, etc.) should be open for extension but closed for modification. This means that new functionality can be added to an existing software entity without having to modify the existing code. This is important because it helps to prevent code breakage and makes code more maintainable.

16. What is the Law of Demeter? Why is it important?

The Law of Demeter is a design principle that states that an object should only interact with other objects that are immediately related to it. This helps to keep objects decoupled from each other, which makes code more maintainable and easier to change.

17. What are some benefits of loosely coupled classes?

Loosely coupled classes are easier to maintain and test because they are not dependent on each other. This means that changes to one class will not necessarily affect other classes, and that classes can be tested in isolation from each other. This also makes it easier to reuse individual classes in different contexts.

18. What are some disadvantages of tightly coupled classes?

Tightly coupled classes can be difficult to maintain and test because they are so interdependent. If you need to make a change to one class, it can have a ripple effect on other classes, and this can make it difficult to predict how the system will behave. Additionally, tightly coupled classes can make it difficult to reuse code because you often need to use the entire system of classes rather than just one or two classes.

19. What’s your favorite type of project and why?

I really enjoy working on projects that are well organized and have a clear structure. I like being able to see the big picture and how all the pieces fit together. I also enjoy working on projects that are challenging and require me to think outside the box.

20. If you were hired by our company and had no other responsibilities but to write code for our applications, what would you do each day?

I would spend my time reading code that already exists, understanding how it works, and thinking about how I could improve it. I would also spend time writing new code and unit tests. I would also spend time talking to other developers about code design and architecture.