Design Patterns Quiz - Multiple Choice Questions (MCQ)

Design patterns represent the best practices used by experienced object-oriented software developers. These patterns solve common design problems and reduce the complexities in our code. This quiz has been curated to test your knowledge about these design patterns.

This Design Patterns quiz consists of 25+ multiple-choice questions (MCQ) with answers and explanations.

1. What is a design pattern in software development? 

A) A fixed set of coding rules 

B) A general reusable solution to a commonly occurring problem 

C) A specific coding style 

D) None of the above 

Answer: 

B) A general reusable solution to a commonly occurring problem 

Explanation: 

In software engineering, a design pattern is a general repeatable solution to a commonly occurring problem. It is a description or template for how to solve a problem that can be used in many different situations. 

2. How many types of design patterns are there? 

A) 3 

B) 5 

C) 8 

D) 10 

Answer: 

A) 3 

Explanation: 

There are three types of design patterns: Creational, Structural, and Behavioral. 

3. What is the main benefit of using a design pattern? 

A) It reduces the total codebase 

B) It allows for the separation of responsibilities 

C) It ensures that the code is easier to understand and debug 

D) All of the above 

Answer: 

D) All of the above 

Explanation: 

Design patterns can provide code that is easy to understand and debug, reduce the total codebase, and ensure the separation of responsibilities. 

4. Which of the following is NOT a creational design pattern? 

A) Singleton Pattern 

B) Factory Pattern 

C) Bridge Pattern 

D) Prototype Pattern 

Answer: 

C) Bridge Pattern

Explanation: 

The Bridge pattern is not a creational design pattern. It is a structural design pattern that separates an object’s interface from its implementation. 

5. Which of the following is a behavioral design pattern? 

A) Observer Pattern 

B) Composite Pattern 

C) Flyweight Pattern 

D) Builder Pattern 

Answer: 

A) Observer Pattern 

Explanation: 

The Observer pattern is a behavioral design pattern that allows an object, called the subject, to notify other objects, called observers, about the changes in its state.

6. What is a Singleton design pattern? 

A) A design pattern that allows you to ensure that a class has only one instance 

B) A design pattern that lets you fit more objects into the available amount of RAM 

C) A design pattern that separates an object's specification from its implementation 

D) A design pattern that ensures that the class has multiple instances 

Answer: 

A) A design pattern that allows you to ensure that a class has only one instance. 

Explanation: 

The singleton design pattern is a type of creational pattern that lets you ensure that a class has only one instance while providing a global access point to this instance.

7. Which of the following best describes the Factory Pattern in design patterns? 

A) It is used to create duplicate objects while keeping performance in mind. 

B) It involves a single class that is responsible to join functionalities of independent or incompatible interfaces. 

C) It restricts the instantiation of a class and ensures that only one instance of the class exists. 

D) It allows an object to be created without exposing the creation logic to the client and the created object is referred to using a common interface. 

Answer: 

D) It allows an object to be created without exposing the creation logic to the client and the created object is referred to using a common interface. 

Explanation: 

The Factory Pattern is a creational pattern that provides an interface for creating objects in a superclass but allows subclasses to alter the type of objects that will be created. The Factory Method hides the instantiation process and returns the instance of the class as an interface, which represents the newly created object. This allows for a lot of flexibility while still providing loose coupling and consistency.

8. What is the use of the Builder Pattern?

A) It simplifies the creation of complex objects by breaking the creation process into steps. 

B) It allows an object to alter its behavior when its internal state changes. 

C) It ensures a class has only one instance and provides a global point of access to it. 

D) It helps in hiding the complexities of the system and provides an interface to the client. 

Answer: 

A) It simplifies the creation of complex objects by breaking the creation process into steps. 

Explanation: 

The Builder Pattern is often used to construct complex objects step by step. It separates the construction of an object from its representation, so the same construction process can create different representations. It's really useful when a constructor has many parameters, some of which might have default values. Instead of dealing with many constructor variants, the builder encapsulates the construction logic within itself.

9. What is the primary purpose of the Abstract Factory design pattern in software design? 

A) It provides an interface for creating families of related or dependent objects without specifying their concrete classes. 

B) It ensures that a class only has one instance and provides a global point of access to it. 

C) It defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically. 

D) It decouples an abstraction from its implementation so that the two can vary independently. 

Answer: 

A) It provides an interface for creating families of related or dependent objects without specifying their concrete classes. 

Explanation: 

The Abstract Factory pattern provides a way to encapsulate a group of individual factories that have a common theme, without specifying their concrete classes. In normal usage, the client software creates a concrete implementation of the abstract factory and then uses the generic interface of the factory to create the concrete objects that are part of the theme. The client does not know (or care) which concrete objects it gets from each of these internal factories, since it uses only the generic interfaces of their products.

10. What is the primary purpose of the Prototype Pattern in design patterns? 

A) To provide a mechanism for creating, deleting, and managing classes at runtime. 

B) To create a clone of an existing object rather than creating a new one, typically for performance reasons. 

C) To provide a simple way to represent hierarchical relationships between objects. 

D) To provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation. 

Answer: 

B) To create a clone of an existing object rather than creating a new one, typically for performance reasons. 

Explanation: 

The Prototype Pattern is a creational design pattern that allows objects to be created by copying a prototype instance at run time. This pattern is used when the type of objects to create is determined by a prototypical instance, which is cloned to produce new objects. This is especially beneficial when object creation is a time-consuming process and we want to optimize performance by minimizing new object creation.

11. What is the primary function of the Adapter design pattern in software development? 

A) It allows classes with incompatible interfaces to work together by wrapping its own interface around that of an already existing class. 

B) It ensures that a class only has one instance and provides a global point of access to it. 

C) It provides an interface for creating families of related or dependent objects without specifying their concrete classes. 

D) It allows for the dynamic addition of new operations to objects without modifying the classes. 

Answer: 

A) It allows classes with incompatible interfaces to work together by wrapping its own interface around that of an already existing class. 

Explanation: 

The Adapter pattern works as a bridge between two incompatible interfaces. This type of design pattern comes under structural pattern as this pattern combines the capability of two independent interfaces. This pattern involves a single class, called adapter which is responsible for communication between two independent or incompatible interfaces.

12. Which pattern helps in reducing complex conditional logic? 

A) Strategy pattern 

B) Observer pattern 

C) Factory pattern 

D) Proxy pattern 

Answer: 

A) Strategy pattern 

Explanation: 

Strategy pattern allows to select an algorithm at runtime. Thus, it helps in eliminating/avoiding complex conditional statements. 

13. The Decorator design pattern is also known as: 

A) Wrapper 

B) Virtual Proxy 

C) Ghost 

D) Pseudo Proxy 

Answer: 

A) Wrapper 

Explanation: 

The Decorator pattern is also known as Wrapper because it's used to wrap an object to add new behavior to it.

14. Which structural pattern should be used when you want to add responsibilities to an object dynamically? 

A) Bridge 

B) Composite 

C) Decorator 

D) Adapter 

Answer: 

C) Decorator 

Explanation: 

A Decorator pattern can be used to attach additional responsibilities to an object either statically or dynamically. A Decorator provides an enhanced interface to the original object.

15. Which of the following best describes the Composite design pattern? 

A) The Composite pattern composes objects into tree structures to represent part-whole hierarchies. 

B) The Composite pattern defines an interface for creating families of related or dependent objects without specifying their concrete classes. 

C) The Composite pattern decouples an abstraction from its implementation so that the two can vary independently. 

D) The Composite pattern provides a way to access the elements of a collection object in a sequential manner without any need to know its underlying representation. 

Answer: 

A) The Composite pattern composes objects into tree structures to represent part-whole hierarchies.

 Explanation: 

The Composite pattern is a structural design pattern that lets you compose objects into tree structures and then work with these structures as if they were individual objects. This pattern is particularly useful for representing part-whole hierarchies.

16. Which design pattern provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation? 

A) Proxy pattern 

B) Observer pattern 

C) Iterator pattern 

D) Strategy pattern 

Answer: 

C) Iterator pattern 

Explanation: 

The Iterator design pattern provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation.

17. Which pattern is specifically concerned with communication between objects? 

A) Mediator 

B) Decorator 

C) Factory 

D) Command 

Answer: 

A) Mediator

Explanation: 

The mediator pattern is used to reduce communication complexity between multiple objects or classes. The pattern provides a mediator class that handles all the communications between different classes.

18. In which pattern does a surrogate or placeholder class control access to the original object? 

A) Adapter 

B) Proxy 

C) Decorator 

D) Bridge 

Answer: 

B) Proxy 

Explanation: 

The Proxy pattern provides a surrogate or placeholder for another object to control access to it. 

19. Which structural design pattern decouples an abstraction from its implementation so that the two can vary independently? 

A) Adapter 

B) Bridge 

C) Composite 

D) Facade 

Answer: 

B) Bridge 

Explanation: 

The Bridge pattern decouples an abstraction from its implementation so that the two can vary independently.

20. Which pattern allows an object to change its behavior when its internal state changes? 

A) State 

B) Strategy 

C) Visitor 

D) Composite 

Answer: 

A) State 

Explanation: 

The State pattern allows an object to change its behavior when its internal state changes. The object will appear to change its class.

21. Which behavioral design pattern should be used when a behavior among objects should be encapsulated and made to operate on an object structure? 

A) Visitor 

B) Strategy 

C) Observer 

D) Command 

Answer: 

A) Visitor 

Explanation: 

The Visitor pattern represents an operation to be performed on the elements of an object structure without changing the classes on which it operates. 

22. Which behavioral design pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable? 

A) Strategy 

B) Observer 

C) Mediator 

D) State 

Answer: 

A) Strategy 

Explanation: 

The Strategy pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable. Strategy lets the algorithm vary independently from clients that use it. 

23. Which design pattern is used when there is a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically?

A) Observer 

B) State 

C) Visitor 

D) Command 

Answer: 

A) Observer 

Explanation: 

The Observer pattern defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically. 

24. Which design pattern would you use to encapsulate a request as an object? 

A) Decorator Pattern 

B) Command Pattern 

C) Singleton Pattern 

D) Bridge Pattern 

Answer: 

B) Command Pattern 

Explanation: 

The Command Pattern encapsulates a request as an object, thereby letting users parameterize clients with queues, requests, and operations, and allowing supporting undoable operations.

25. What is Template Design Pattern? 

A) It defines the skeleton of an algorithm in a method, deferring some steps to subclasses. 

B) It ensures that a class has only one instance and provides a global point of access to it. 

C) It encapsulates a request as an object, thereby allowing for the parameterization of clients with queues, requests, and operations. 

D) It provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation. 

Answer: 

A) It defines the skeleton of an algorithm in a method, deferring some steps to subclasses. 

Explanation: 

The Template design pattern is a behavioral design pattern that defines the skeleton of an algorithm in the superclass but lets subclasses override specific steps of the algorithm without changing its structure.