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Table of contents
1.
Introduction
2.
Design Patterns Interview Questions for Freshers 
2.1.
Q1. What is a design pattern?
2.2.
Q2. Explain the Singleton design pattern.
2.3.
Q3. Explain the Factory Method design pattern.
2.4.
Q4. Explain the Builder design pattern.
2.5.
Q5. Explain the Prototype design pattern.
2.6.
Q6. Explain the Facade design pattern.
2.7.
Q7. Explain the Flyweight design pattern.
2.8.
Q8. Explain the State design pattern.
2.9.
Q9. Explain the purpose of design patterns in the software Industry.
2.10.
Q10. What are the different categories of design patterns?
2.11.
Q11. Explain the Abstract Factory design pattern.
2.12.
Q12. Explain the Adapter design pattern.
2.13.
Q13. Explain the Bridge design pattern.
2.14.
Q14. Explain the Decorator's design pattern.
2.15.
Q15. Explain the Proxy design pattern.
3.
Design Patterns Interview Questions for Experienced
3.1.
Q16. Explain the Chain of Responsibility design pattern.
3.2.
Q17. Explain the Interpreter design pattern.
3.3.
Q18. What is the Iterator design pattern?
3.4.
Q19. What is the Mediator design pattern?
3.5.
Q20. What is the Memento design pattern?
3.6.
Q21. What is the Observer design pattern?
3.7.
Q22. Explain the Command design pattern.
3.8.
Q23. What is the Strategy design pattern?
3.9.
Q24. What is the Template Method design pattern?
3.10.
Q25. What is the Visitor design pattern?
3.11.
Q26. How do you choose the appropriate design pattern for a given problem?
3.12.
Q27. Describe how you've used a design pattern in the real world.
3.13.
Q28. How do design patterns help reduce the coupling between components in a system?
3.14.
Q29. How do design patterns make it easier to reuse code in software development?
3.15.
Q30. Can you explain the Composite design pattern?
4.
Conclusion
Last Updated: Jun 12, 2024

Design Patterns Interview Questions

Author Vivek Tiwari
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18 Jun, 2024 @ 01:30 PM

Introduction

Welcome, ninjas. In software development, it's important to be familiar with design pattern interview questions. Design patterns are a popular topic in interviews. It allows developers to solve common programming problems like the reusability of code. This article will cover the most frequently asked design pattern interview questions, including their definition, usage, and implementation. 

Image showing Interview Question on Design Pattern

No matter whether you're a beginner or an experienced developer. Understanding these concepts is crucial for landing your dream job in software development. So, let's dive in and explore the design pattern interview questions!

Design Patterns Interview Questions for Freshers 

Let’s discuss some beginner-level design pattern interview questions:

Q1. What is a design pattern?

Answer: design pattern is a way of solving a common problem in software development. It is a reusable solution that can be applied to a specific problem in a given context.

Q2. Explain the Singleton design pattern.

Answer: The Singleton design pattern ensures that only one class instance can be created and provides a global access point to that instance. This is useful when you need only one class instance in your program, such as for a global configuration or a database connection.

Q3. Explain the Factory Method design pattern.

Answer: The Factory Method design pattern provides an interface for creating objects but allows subclasses to decide which class to instantiate. This is useful when you need to create similar objects with different implementations. The Factory Method pattern lets you create objects without specifying their exact class, so you can easily switch between different implementations.

Q4. Explain the Builder design pattern.

Answer: The Builder design pattern separates the construction of an object from its representation, allowing for different representations to be created using the same construction process. This is useful when you need to create complex objects that have many parts or options. The Builder pattern lets you create objects step-by-step, allowing for more flexibility in constructing the object.

Q5. Explain the Prototype design pattern.

Answer: The Prototype design pattern creates new objects by cloning existing ones instead of creating them from scratch. This is useful when creating new objects is expensive or time-consuming. The Prototype pattern allows you to create new objects quickly by copying an existing object.

Q6. Explain the Facade design pattern.

Answer: The Facade design pattern provides a simple interface to a complex system, hiding its complexity from the user. It is useful when you have a system that is difficult to use or understand. The Facade pattern lets you provide a simplified interface that shields the user from the underlying complexity.

Q7. Explain the Flyweight design pattern.

Answer: The Flyweight design pattern minimizes memory usage by sharing data among multiple objects. This is useful when you need to create many similar objects that have some shared data. The Flyweight pattern lets you share the common data among multiple objects, reducing your program's memory footprint.

Q8. Explain the State design pattern.

Answer: The State design pattern allows an object to change its behavior based on its internal state. This is useful when you have an object in different states, and each state requires different behavior. The State pattern lets you define different states for the object and allows the object to switch between states at runtime.

Q9. Explain the purpose of design patterns in the software Industry.

Answer: Design patterns help developers solve common problems in software development, leading to better code quality, maintainability, and reusability. Using design patterns, developers can create more efficient and effective code that is easier to maintain and modify.

Q10. What are the different categories of design patterns?

Answer: The different categories of design patterns include creational, structural, and behavioral patterns. Creational patterns deal with object creation, structural patterns deal with object composition, and behavioral patterns deal with object interaction and communication. Each category includes several patterns that address specific problems in software development.

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Q11. Explain the Abstract Factory design pattern.

Answer: The Abstract Factory design pattern creates families of related objects without specifying their concrete classes. It allows for more flexibility in the design of the software, as it separates the process of object creation from the rest of the program. The pattern involves creating an abstract class or interface that defines the methods for creating objects, which can then be implemented by concrete classes that make specific types of things.

Q12. Explain the Adapter design pattern.

Answer: The Adapter design pattern converts the interface of one class into another interface that a client expects, allowing classes to work together that couldn't otherwise because of incompatible interfaces. This pattern involves creating a wrapper class that implements the desired interface and passes requests to the original class using the adapted interface.

Q13. Explain the Bridge design pattern.

Answer: The Bridge design pattern decouples an abstraction from its implementation, allowing you to change or extend the performance without affecting the abstraction. This pattern involves creating two separate class hierarchies: one for abstraction and one for implementation. The abstraction class references an object of the implementation class, which it uses to delegate the performance of its methods.

Q14. Explain the Decorator's design pattern.

Answer: The Decorator design pattern adds functionality to an object at runtime without affecting the behavior of other things of the same class. This pattern involves creating a decorator class. The decorator class and original class have the same interface and wrap the original object to add additional behavior.

Q15. Explain the Proxy design pattern.

Answer: The Proxy design pattern provides a surrogate or placeholder object to control access to a thing, which can be helpful in scenarios such as remote method invocation or resource-limited environments. This pattern involves creating a proxy class. The proxy class is an intermediate between the real objects and clients. Implementing the same interface as the actual object and forwarding requests to it.

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Design Patterns Interview Questions for Experienced

Q16. Explain the Chain of Responsibility design pattern.

Answer: The Chain of Responsibility design pattern is used to pass requests along a dynamic chain of receivers until one of them handles the request. It reduces the coupling between sender and receiver and gives you more control over who handles a request and when. This pattern involves creating a chain of receiver objects that each can take the request or pass it on to the following receiver in the chain.

Q17. Explain the Interpreter design pattern.

Answer: The Interpreter design pattern implements a specialized language, allowing you to interpret sentences in that language. This pattern involves defining the grammar for the language and creating an interpreter class that can parse and interpret sentences according to the grammar.

Q18. What is the Iterator design pattern?

Answer: The Iterator design pattern is a way to go through all the things in a group one by one without needing to know how the group is set up. For example, you have a backpack with different things, like a book, a water bottle, and a snack. With the Iterator design pattern, you can look at each item in the backpack individually without knowing how the backpack is organized.

Q19. What is the Mediator design pattern?

Answer: The Mediator design pattern is like a manager who helps different things work together without them having to talk to each other directly. For example, let's say you have a group of people playing a game, and they need to speak to each other to play the game. Instead of everyone talking to everyone else, a mediator (like a game referee) can help them communicate and work together more efficiently.

Q20. What is the Memento design pattern?

Answer: The Memento design pattern is like saving a video game at a certain point so you can return to that point later. With the Memento design pattern, you can save the state of something (like a game or an app) at a certain point and then return to that point later if needed. This can be useful if you want to adopt a different path or undo something.

Must Read: Ab Initio Interview Questions

Q21. What is the Observer design pattern?

Answer: The Observer pattern is a design pattern that allows one or more objects (called observers) to be notified when a subject (the thing being watched) changes. This pattern is useful when multiple objects need to know when a change has occurred in another object. For example, in a weather application, multiple displays might need to update when the temperature changes. The Observer pattern helps to decouple the subject and observers, making it easier to maintain and modify the code.

Q22. Explain the Command design pattern.

Answer: The Command design pattern encapsulates a request as an object, allowing you to parameterize clients with different requests, queue or log requests, and support undo-redo functionality. This pattern involves creating a command interface that defines the methods for executing and undoing the command and concrete command classes that implement the interface for specific types of commands.

Q23. What is the Strategy design pattern?

Answer: The Strategy design pattern is like choosing a different way to solve a problem depending on the situation. With the Strategy design pattern, you can have other ways to solve a problem and decide which one to use based on what's happening. For example, if you need to get through a level in a game, you can choose different strategies depending on your obstacles.

Q24. What is the Template Method design pattern?

Answer: The Template Method design pattern is like a recipe where you can change some ingredients depending on your liking. With the Template Method design pattern, you can have a general way of doing something (like cooking a meal), but you can change certain parts to make it fit your needs. For example, you can have a recipe for pancakes, but you can change the toppings to make them taste different.

Q25. What is the Visitor design pattern?

Answer: The Visitor design pattern is like having a helper who can do different tasks depending on your needs. With the Visitor design pattern, you can have an object that can do various operations on other objects without changing the things themselves. For example, if you have a bunch of animals, you can have a visitor who can feed or play with them without changing the animals themselves.

Q26. How do you choose the appropriate design pattern for a given problem?

Answer: Choosing the appropriate design pattern for a problem depends on the problem you are trying to solve. For example, if you need to control the flow of an application, use the State pattern. It allows an object to change its behavior based on its internal state. If you need to maintain a single instance of an object throughout the lifetime of an application, use the Singleton pattern.

Q27. Describe how you've used a design pattern in the real world.

Answer: Design patterns are reusable solutions to common problems in software development. I used the Singleton pattern in a coding project, ensuring that only one class instance was created. This helped me avoid problems that could have occurred if multiple instances of the same class had been created.

Q28. How do design patterns help reduce the coupling between components in a system?

Answer: When different computer program parts are "coupled" too tightly, things are harder to change and more likely to break. Design patterns help solve this problem by ensuring that each part only depends on a few other factors, making it easier to swap things out or make changes without breaking everything.

Q29. How do design patterns make it easier to reuse code in software development?

Answer: When people write computer programs, they often run into similar problems over and over again. Design patterns are like little templates for solving these common problems; they've been tested and proven to work well. So, instead of writing new code every time, developers can use a design pattern to solve the problem in a tried-and-true way.

Q30. Can you explain the Composite design pattern?

Answer: Sure! The Composite design pattern is about building complex structures out of simple parts. It's like building with Legos! Each Lego brick is a simple object, but you can combine them in many ways to make more extensive and complex structures. In computer programming, the Composite design pattern is used to build things like graphical user interfaces (the buttons, menus, and windows you click on when you use a computer) or file systems (the way your computer stores and organizes files).

Conclusion

In conclusion, design patterns are essential for software development, and if you want to be a great software developer, you need to understand them. This article on design pattern interview questions gave you some questions that might arise in a technical interview. If you review these questions and learn about design patterns and how to use them in real-life situations. You can leave a good impact on your interviewer. Just keep practicing and learning about design patterns. You'll be ready to tackle any design challenge that comes your way!

It was all about the design pattern interview questions. From this, you can relate to the questions you will face during the interview rounds and understand the computer science fundamentals. 

Recommended Readings:

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Happy Learning, Ninjas.

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