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Table of contents
1.
Introduction
2.
Beginner-Level Interview Questions
3.
Intermediate-Level Interview Questions
4.
Advanced Level Interview Questions
5.
Conclusion
Last Updated: Jun 12, 2024

Java design patterns interview questions

Author Vivek Tiwari
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Introduction

As a software engineer, knowing about java design patterns is essential. These different ways to write code make it easier to work with and use again later. Java programming uses design patterns a lot to make the code better.

Interview Questions

If you're getting ready for a Java interview, you should be ready to answer questions about design patterns. This blog on Java design patterns interview questions can help you prepare by discussing some common questions you might get asked. It doesn't matter if you're new to Java or have been doing it for a while. This blog can help you learn more about design patterns and be ready for your interview!

Also see,  Operating System Interview Questions

Beginner-Level Interview Questions

Let’s discuss some Beginner-level java design patterns interview questions: 

 

Q1. Can you discuss the Command design pattern in Java?

Answer: The Command design pattern is used in Java to encapsulate a request as an object. This means that instead of just giving a command directly, we wrap it up as an object that we can then pass around and do different things with. This allows us to do things like queue up commands to be executed later or even undo commands already executed.

Q2. Can you explain the Chain of Responsibility design pattern in Java?

Answer: The Chain of Responsibility pattern allows a series of objects to handle a request or event. Each object in the chain can handle the request or pass it on to the next one until it is handled.

Q3. Can you explain the Singleton design pattern in Java?

Answer: The Singleton design pattern ensures that only one instance of a class is created and globally accessible. In Java, this pattern is implemented by creating a private constructor and a getInstance() method that returns the single instance of the class.

Q4. What is a design pattern in software engineering?

Answer: A design pattern is a general, reusable solution to a common problem in software design. It provides a way to solve problems that is efficient, flexible, and maintainable.

Q5. How is the Facade design pattern used in Java to simplify interfaces for complex subsystems?

Answer: The Facade design pattern is used in Java to provide a simplified interface to a complex subsystem of classes. This means that instead of knowing about all the different classes and methods involved in the subsystem, we can use a single interface that handles everything. This makes it easier to use the subsystem and reduces the chances of making mistakes.

Q6. What are the differences between the Class Adapter and Object Adapter design patterns in Java?

Answer: The Class Adapter and Object Adapter design patterns in Java adopt one class's interface to another. The difference is in how they do it. The Class Adapter design pattern uses inheritance to adapt the interface. This means that the adapter class is a subclass of the class it's adapting. The Object Adapter design pattern uses composition to adapt the interface. This means that the adapter class contains an instance of the class it's adapting and calls its methods to provide the new interface.

Q7. Can you explain how the Decorator design pattern is implemented in Java to add functionality to existing objects?

Answer: The Decorator design pattern is used in Java to add new functionality to an existing object without changing its structure. This means we can add new features to an object without modifying its code directly. To implement this pattern, we create a new class (the decorator) that takes an existing object as a parameter. The decorator then adds new functionality to the object by calling its methods and doing additional things before or after the method call. This allows us to add new features to an object without changing its underlying code, which is especially useful when we don't have access to the source code.

Q8. What is the Observer design pattern in Java, and how is it used to manage dependencies between objects?

Answer: The Observer design pattern in Java manages dependencies between objects. In this pattern, one object (the subject) keeps track of other objects (the observers) that must be notified whenever it changes. When the subject changes, it notifies all the observers, which can then take some action based on the new information. This pattern is useful because it allows us to decouple objects that must work together. Instead of having objects directly call each other's methods, they can be observers of each other and respond to changes when they happen.

Must read topic, Kotlin Interview Questions

Q9. What's the difference between the Abstract Factory and Factory design patterns?

Answer: The Abstract Factory design pattern creates families of related objects without specifying their concrete classes. In contrast, the Factory design pattern creates a single object without exposing the creation logic.

Q10. What's the difference between the Template Method and Strategy design patterns?

Answer: The Template Method design pattern defines the skeleton of an algorithm in a method while allowing subclasses to provide specific implementations of some steps. In contrast, the Strategy design pattern defines a family of algorithms and allows them to be interchanged at runtime.

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Intermediate-Level Interview Questions

Let’s discuss some Intermediate-level java design patterns interview questions:

 

Q11. What is the Adapter design pattern in Java?

Answer: The Adapter pattern allows incompatible classes to work together by wrapping an object with an interface compatible with another object. This allows the two objects to communicate without changing their interfaces.

Q12. What is the Memento design pattern in Java?

Answer: The Memento pattern provides a way to capture and restore an object's internal state without violating encapsulation. It allows an object to be restored to its previous state, even after changes.

Q13. Can you explain the Visitor design pattern in Java?

Answer: The Visitor pattern separates an algorithm from an object structure on which it operates. It allows new operations to be added to an object structure without changing its classes.

Q14. Can you discuss the State design pattern in Java?

Answer: The State pattern allows an object to alter its behavior when its internal state changes. It encapsulates the states of an object as separate classes and allows the object to change its state by changing its current class.

Q15. What is the Factory design pattern, and when would you use it?

Answer: The Factory pattern defines an interface for creating objects but allows subclasses to decide which class to instantiate. It is useful when the exact class of an object is known in runtime.

Q16. How are design patterns used in the Model-View-Controller (MVC) architecture?

Answer: MVC is a software architecture that separates an application's data, user interface, and control logic into three distinct components. Design patterns, such as Observer and Factory, implement the communication and interaction between these components.

Q17. Can you discuss the Iterator design pattern in Java?

Answer: The Iterator pattern provides a way to access the elements of a collection without exposing its underlying implementation. It also allows the collection to be traversed in different ways.

Q18. What is the Mediator design pattern in Java?

Answer: The Mediator pattern defines an object that encapsulates how objects interact. It promotes loose coupling between the objects by preventing them from directly referencing each other.

Q19. Can you explain the Interpreter design pattern in Java?

Answer: The Interpreter design pattern in Java is used to define a language's grammar and provide an interpreter for that language. This means we can create a new language with its own rules and syntax and then write an interpreter that can understand and execute programs in that language. To implement this pattern, we create classes representing the language's grammar (e.g., the different types of statements, expressions, etc.). We also create a parser that can read input written in the language and turn it into a series of objects representing the program. Once these pieces are in place, we can use the interpreter to execute the program and get the desired output.

Q20. Can you explain the Bridge design pattern in Java?

Answer: The Bridge design pattern in Java is used to decouple an abstraction (i.e., the way we use an object) from its implementation (i.e., the way the object works). This means we can use an object differently without changing its implementation. To implement this pattern, we create an abstraction class defining the interface for using the object. We then create a separate implementation interface that defines the object's operations. Finally, we create a bridge class that connects the abstraction and implementation interfaces, allowing us to use the object differently without changing the underlying implementation.

For example, we could use a bridge to connect a drawing program to different graphics libraries (e.g., Java2D, OpenGL, etc.), allowing us to use the same program to draw different things without having to rewrite the entire program each time.

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Advanced Level Interview Questions

Let’s discuss some Advance-level java design patterns interview questions:

 

Q21. Can you explain the Flyweight design pattern in Java?

Answer: The Flyweight design pattern is used to reduce the memory usage of an application by sharing common objects instead of creating new ones. In Java, this pattern is implemented by creating a FlyweightFactory that stores a pool of shared objects and a Flyweight interface that defines the operations that can be performed on these objects.

Q22. What is the Template Method design pattern in Java?

Answer: The Template Method design pattern provides a template for an algorithm in a superclass that subclasses can customize. It allows for easy maintenance and modification of the algorithm by changing only the specific steps that need to be modified in the subclasses. An example is the java.util.Collections.sort() method.

Q23. Can you explain the Builder design pattern in Java?

Answer: The Builder's design pattern separates the construction of a complex object from its representation. So that different representations can be created using the same construction process. In Java, this pattern is implemented by creating a Builder class with methods for setting the different attributes of the built object and a build() method that returns the constructed object.

Q24. Can you discuss the Proxy design pattern in Java?

Answer: The Proxy design pattern controls access to an object by creating a surrogate object that acts as a placeholder for the real object. In Java, this pattern is implemented by creating a Proxy class that implements the same interface as the real object and delegates method calls to the real object.

Q25. Can you discuss the Composite design pattern in Java?

Answer: The Composite design pattern treats a group of objects as a single object, allowing them to be manipulated uniformly. In Java, this pattern is implemented by creating a Component interface. That defines the operations that can be performed and multiple classes that implement the interface. To provide different implementations of the operations.

Q26. Can you discuss the Prototype design pattern in Java?

Answer: The Prototype design pattern creates new objects by copying existing objects rather than creating them from scratch. In Java, this pattern is implemented by creating a prototype interface that defines a clone() method and multiple classes that implement the interface to provide different implementations of the clone() method.

Q27. Can you give an example of a design pattern in Java?

Answer: For example, the Observer pattern is used in Java's Swing framework, where components register as observers of events on other components. When the event occurs, the observers are notified and can react accordingly.

Q28. What is the difference between creational and structural design patterns?

Answer: Creational patterns deal with the process of object creation and initialization. Structural patterns deal with the composition of classes and objects to form larger structures.

Q29. What is the Strategy design pattern in Java?

Answer: The Strategy design pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable. In Java, this pattern is implemented by creating an interface that defines the operations that can be performed.  Multiple classes implement the interface to provide different implementations of the operations.

Q30. Can you discuss the benefits and limitations of using design patterns in Java software development?

Answer: Using design patterns in Java development has benefits like reusability, maintainability, scalability, consistency, and team collaboration. However, overusing them can make the code unnecessarily complex, and learning and implementing them can be time-consuming. Also, not all patterns may apply to a specific project, and using them may lead to rigid code that is not easily adaptable to changing requirements. Despite their limitations, design patterns can offer substantial advantages when used judiciously in Java software development.

Conclusion

Ninjas If you're preparing for a job interview on Java design patterns. It can be a bit scary. But don't worry. We've got you covered. This blog on java design patterns interview questions has many questions and answers. Studying and practicing these questions will make you feel more ready and confident for the interview. Remember, there's nothing to be afraid of. With our guide. You'll be able to answer all the java design patterns interview questions you will face during your interview.

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