Top 250 Design Patterns Interview Questions and Answers

OOPS, Design Pattern and algorithm design are important concepts in software development.

• OOPS (Object-Oriented Programming) is a programming paradigm that uses objects to represent real-world entities.

• Design Patterns are reusable solutions to common software design problems.

• Algorithm design involves creating step-by-step instructions for solving a problem.

• Examples of design patterns include Singleton, Factory, and Observer.

• Examples of algorithms include sorting algorithms lik...read more

Shared viewmodel is a design pattern used in software development to share data between different components.

• Shared viewmodel allows multiple components to access and modify the same data

• It helps in keeping the data consistent across different parts of the application

• Example: Using a shared viewmodel in a shopping cart application to update the total price when items are added or removed

Best design practices in architecture involve considering functionality, aesthetics, sustainability, and user experience.

• Consider the functionality of the space and how it will be used by occupants

• Focus on creating aesthetically pleasing designs that enhance the environment

• Incorporate sustainable materials and practices to reduce environmental impact

• Prioritize user experience and ensure the design meets the needs of the people using the space

The design pattern used for an app and its architecture is crucial for scalability and maintainability.

• Use MVC (Model-View-Controller) for separating data, presentation, and user interaction.

• Consider MVVM (Model-View-ViewModel) for better separation of concerns and testability.

• Implement Dependency Injection to make components loosely coupled and easier to test.

• Use Singleton pattern for managing shared resources like network calls or database connections.

• Consider using Clean A...read more

To handle scale and latency issues, we use design patterns like load balancing, caching, and asynchronous processing.

• Load balancing distributes traffic across multiple servers to prevent overload.

• Caching stores frequently accessed data in memory to reduce latency.

• Asynchronous processing allows tasks to be executed in the background, freeing up resources for other tasks.

• We also use horizontal scaling, sharding, and partitioning to handle large amounts of data.

• Examples of tools...read more

The design pattern for API flow involves defining the structure and sequence of API calls.

• Identify the required API endpoints and their parameters

• Determine the order and dependencies of API calls

• Handle error scenarios and implement error handling mechanisms

• Consider authentication and authorization requirements

• Implement data caching and request throttling if necessary

Low level design for a chess game including classes, functions, and data structures.

• Create classes for pieces (e.g. Pawn, Rook, Bishop) with properties like position and color

• Implement functions for moving pieces, checking valid moves, and capturing opponent pieces

• Use data structures like 2D arrays to represent the chess board and track piece positions

Design patterns are reusable solutions to common software problems.

• Creational patterns: Singleton, Factory, Abstract Factory

• Structural patterns: Adapter, Decorator, Facade

• Behavioral patterns: Observer, Strategy, Command

• Examples: MVC, Dependency Injection, Template Method

Design patterns in .NET Core are reusable solutions to common problems in software design.

• Some common design patterns in .NET Core include Singleton, Factory, Observer, and Strategy.

• Design patterns help in creating maintainable, scalable, and efficient code.

• They promote code reusability and separation of concerns.

• Examples: Singleton pattern ensures a class has only one instance, Factory pattern creates objects without specifying the exact class, Observer pattern defines a one...read more

A media player design framework should prioritize user experience, ease of use, and accessibility.

• Include intuitive controls for playback, volume, and playlist management

• Ensure compatibility with a variety of media formats

• Consider incorporating features such as equalizer settings and visualizations

• Design for accessibility with options for closed captioning and audio descriptions

• Prioritize a clean and visually appealing interface

ASP.NET MVC follows the Model-View-Controller (MVC) design pattern.

• MVC separates application into three components: Model, View, and Controller

• Model represents data and business logic

• View represents user interface

• Controller handles user input and updates the model and view accordingly

• MVC promotes separation of concerns and modularity

• Examples of popular MVC frameworks include ASP.NET MVC, Ruby on Rails, and Spring MVC

I have implemented design patterns like Singleton, Factory, and Observer in various projects.

• Implemented Singleton pattern to ensure only one instance of a class exists.

• Utilized Factory pattern to create objects without specifying the exact class of object that will be created.

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

SOLID design principles and Design Patterns are used to create maintainable and scalable software.

• SOLID principles help in creating loosely coupled and modular code.

• Design Patterns provide reusable solutions to common software problems.

• Examples of SOLID principles include Single Responsibility, Open/Closed, and Liskov Substitution.

• Examples of Design Patterns include Factory, Singleton, and Observer.

• Using SOLID principles and Design Patterns can improve code quality, reduce bu...read more

Factory pattern creates objects without exposing the instantiation logic, while Abstract Factory pattern provides an interface for creating families of related objects.

• Factory pattern is a creational design pattern that provides a way to create objects without specifying the exact class of object that will be created.

• Abstract Factory pattern is a creational design pattern that provides an interface for creating families of related or dependent objects without specifying their...read more

IOC stands for Inversion of Control. Its components are Dependency Injection and Aspect Oriented Programming.

• Dependency Injection: injecting dependencies into a class instead of creating them within the class

• Aspect Oriented Programming: separating cross-cutting concerns from the main logic of the application

• Examples: Spring Framework, Guice

Factory facade design patterns are used to provide a simplified interface to a complex system of classes.

• Facade pattern provides a unified interface to a set of interfaces in a subsystem.

• It hides the complexities of the system and provides an easy-to-use interface.

• Examples include Java's JDBC API, which provides a simplified interface to interact with databases.

• Another example is the jQuery library, which provides a simplified interface to manipulate HTML and CSS.

• The Facade p...read more

An architect is responsible for designing and planning buildings and structures.

• Architects create detailed drawings and blueprints for construction projects.

• They work closely with clients to understand their needs and preferences.

• Architects must consider factors such as building codes, safety regulations, and environmental impact.

• They often use computer-aided design (CAD) software to create their designs.

• Architects may specialize in areas such as residential, commercial, or l...read more

Singleton pattern in NestJS ensures a class has only one instance and provides a global point of access to it.

• Use the @Injectable() decorator to mark a class as a singleton in NestJS.

• Inject the singleton class into other classes using the constructor.

• The instance of the singleton class will be shared across the application.

Design patterns are reusable solutions to common problems in software design.

• Design patterns help in creating flexible, maintainable, and scalable code.

• Examples of design patterns include Singleton, Factory, Observer, and Strategy.

• Each design pattern has a specific purpose and can be applied to different scenarios in software development.

Abstract Factory pattern is a design pattern that provides an interface for creating families of related or dependent objects without specifying their concrete classes.

• Provides an interface to create families of related objects

• Decouples the client code from the actual implementation classes

• Promotes code reusability and flexibility

• Examples: GUI libraries where different components like buttons, text fields, etc. are created using a factory

Delegate pattern is a design pattern in which an object delegates some of its responsibilities to another object.

• Create a protocol defining the methods that the delegate should implement

• Declare a delegate property in the delegating class

• Set the delegate property to the object that will act as the delegate

• Call the delegate methods from the delegating class

Yes, components in Adobe Experience Manager are reusable.

• Components can be created once and used multiple times across different pages.

• Changes made to a component will reflect on all instances of that component.

• Components help maintain consistency and save time in content creation.

• Examples: Header, Footer, Call-to-Action buttons.

Notification Observer Design Pattern is used to establish a one-to-many relationship between objects.

• Create a subject class that maintains a list of observers and notifies them of any state changes.

• Observers register themselves with the subject to receive notifications.

• Use protocols and delegates in iOS to implement the observer pattern.

• Example: NotificationCenter in iOS uses the observer pattern to broadcast notifications to registered observers.

NotificationCenter is a system that enables communication between different parts of an application.

• NotificationCenter allows components of an application to communicate without having direct references to each other.

• It uses the observer pattern where objects register themselves as observers for specific notifications.

• Notifications can be posted to the NotificationCenter with optional data.

• Observers can then receive and handle these notifications.

• NotificationCenter is commonl...read more

Design patterns are reusable solutions to common problems in software design. Examples include Singleton, Factory, and Observer.

• Design patterns are solutions to common problems in software design

• They help in creating reusable and maintainable code

• Examples include Singleton, Factory, Observer, and Strategy patterns

Design patterns are used to solve common software design problems. Each use case requires a specific pattern.

• Design patterns are reusable solutions to common software design problems.

• Each use case requires a specific pattern to be used.

• Examples of design patterns include Singleton, Factory, and Observer.

• The choice of pattern depends on the problem being solved and the requirements of the system.

I have experience in implementing saga design patterns and designing saga solutions.

• Saga design pattern is used to manage long-lived transactions across microservices.

• It involves breaking down a transaction into smaller steps or events.

• Each step is handled by a separate microservice.

• If a step fails, the saga coordinator rolls back the previous steps.

• I have implemented saga design patterns using tools like Apache Kafka and RabbitMQ.

Shared pointers are a type of smart pointer used in C++ to manage memory allocation.

• Shared pointers allow multiple pointers to refer to the same object, automatically managing the object's lifetime.

• They use reference counting to keep track of how many pointers are pointing to the object.

• When the last shared pointer goes out of scope, the object is automatically deleted.

• They help prevent memory leaks and dangling pointers.

• Example: std::shared_ptr ptr1 = std::make_shared();

• Exam...read more

Yes, I am familiar with designing modifications.

• I have experience in using CAD software to make modifications to existing designs.

• I am able to analyze the feasibility of proposed modifications and provide recommendations.

• I have worked on projects where modifications were made to improve functionality or reduce costs.

• I am able to communicate effectively with team members and stakeholders to ensure modifications meet requirements.

Event driven design is a software architecture pattern where events trigger actions.

• Events are used to communicate between different components of the system

• Event handlers are responsible for processing events and triggering actions

• Event driven design promotes loose coupling and scalability

• Examples include message queues, pub/sub systems, and reactive programming

• Commonly used in microservices architecture

Integration standard design patterns are used to ensure consistency and efficiency in software integration. Different patterns are applied based on the specific use case.

• Integration patterns include messaging, file transfer, remote procedure invocation, and database integration

• Messaging patterns are used for asynchronous communication between systems

• File transfer patterns are used for batch processing and data exchange

• Remote procedure invocation patterns are used for synchron...read more

Strategy pattern is a behavioral design pattern that allows selecting an algorithm at runtime.

• Used strategy pattern in a shopping cart application to dynamically apply different discount strategies based on user type (e.g. regular customer, premium customer)

• Implemented strategy pattern in a payment processing system to handle different payment methods (e.g. credit card, PayPal, Apple Pay)

• Utilized strategy pattern in a traffic management system to dynamically switch between di...read more

Commands and prompts play a crucial role in the design process, guiding users through the interface and helping them achieve their goals.

• Use clear and concise language to communicate instructions to users

• Provide feedback to confirm actions and guide users on the next steps

• Consider the context in which the commands are presented to ensure they are relevant and helpful

• Utilize visual cues such as icons or animations to enhance the user experience

Design a system to handle data flow efficiently

• Identify the sources of data and how they will be collected

• Determine the processing steps required for the data

• Consider the storage and retrieval mechanisms for the data

• Implement data validation and error handling procedures

• Optimize the data flow for performance and scalability

Considerations in composite design include material selection, fiber orientation, resin type, manufacturing process, and environmental factors.

• Material selection is crucial for desired properties like strength, stiffness, and weight. Examples include carbon fiber, fiberglass, and Kevlar.

• Fiber orientation determines the mechanical properties of the composite. Examples include unidirectional, woven, and random orientations.

• Resin type affects the bonding between fibers and overa...read more

Factory & Builder Design Patterns are creational patterns used in software development to create objects.

• Factory Design Pattern is used to create objects without specifying the exact class of object that will be created.

• Builder Design Pattern is used to construct complex objects step by step.

• Factory pattern uses a factory method to create objects, while Builder pattern uses a builder class to construct objects.

• Factory pattern is a class-based pattern, while Builder pattern is...read more

Designing an offline application involves creating a system that can function without an internet connection.

• Consider the data storage and synchronization methods to ensure data is accessible offline.

• Implement caching mechanisms to store frequently accessed data locally.

• Design a user-friendly interface that clearly indicates when the application is offline.

• Include offline capabilities for essential features to enhance user experience.

• Test the application thoroughly in offline...read more

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Singleton class can be broken using reflection, serialization, cloning, and multi-threading.

• Reflection can be used to access the private constructor and create multiple instances.

• Serialization can create multiple instances when the object is deserialized.

• Cloning can create a new instance of the Singleton class.

• Multi-threading can create multiple instances if not synchronized properly.

MVC lifecycle involves three stages: initialization, request processing, and view rendering.

• Initialization: Controller and model objects are created.

• Request processing: Controller receives and processes user requests, updates the model, and selects the view.

• View rendering: The view is rendered and sent back to the user.

• Example: User requests a webpage, the controller receives the request, updates the model with data from the database, selects the appropriate view, and renders...read more

Singleton pattern restricts the instantiation of a class to a single instance and provides a global point of access to it.

• Create a private constructor to restrict instantiation of the class

• Create a private static instance of the class

• Create a public static method to access the instance

• Ensure thread safety if necessary

• Examples: Database connection, Logger, Configuration settings

Designing a shopping cart involves creating a user-friendly interface for customers to add, view, and manage items for purchase.

• Include features such as adding/removing items, viewing total price, and checking out securely.

• Design a visually appealing and intuitive layout for easy navigation.

• Implement functionality for saving items in cart for future visits.

• Consider options for applying discounts or promo codes.

• Ensure compatibility with various devices and browsers for a seaml...read more

MVVM (Model-View-ViewModel) is a design pattern that separates the user interface from the business logic and data model.

• MVVM consists of three main components: Model, View, and ViewModel.

• The Model represents the data and business logic, the View represents the UI components, and the ViewModel acts as a mediator between the Model and View.

• MVVM helps in achieving separation of concerns, making code more modular and easier to maintain.

• Data binding is a key feature of MVVM, wher...read more

Factory Design pattern is a creational design pattern that provides an interface for creating objects in a superclass, but allows subclasses to alter the type of objects that will be created.

• Factory Design pattern is used to create objects without specifying the exact class of object that will be created.

• It provides a way to delegate the instantiation logic to child classes.

• It promotes loose coupling by eliminating the need to bind application-specific classes into the code.

• E...read more

Factory pattern creates objects without exposing the instantiation logic to the client.

• Create an interface or abstract class for the product

• Create concrete classes implementing the same interface/abstract class

• Create a factory class that returns the product

• Client uses the factory to create the object

Code on patterns

• Use loops to iterate through rows and columns

• Use conditional statements to determine pattern

• Examples: printing a pyramid, diamond, or triangle pattern

Design patterns in Micro services help in solving common architectural challenges.

• Service Registry pattern

• Circuit Breaker pattern

• Gateway pattern

• Saga pattern

• API Gateway pattern

Obser is not a known term in software engineering.

• Obser is not a known term in software engineering.

• It is possible that the interviewer misspoke or meant to ask a different question.

• It is important to clarify any unclear or confusing questions during an interview.

Vending machine design patterns involve creating efficient and user-friendly interfaces for purchasing products.

• Consider using the Factory Method pattern to create different types of vending machines.

• Implement the State pattern to manage the different states of the vending machine (e.g. idle, dispensing, out of stock).

• Use the Observer pattern to notify the vending machine when products are restocked or when a purchase is made.

• Apply the Strategy pattern to allow for different ...read more

MVP focuses on separating concerns by having a presenter handle logic, while MVVM uses data binding to connect view and view model.

• MVP stands for Model-View-Presenter, where the presenter handles logic and updates the view. MVVM stands for Model-View-ViewModel, where data binding connects the view and view model.

• In MVP, the view has a reference to the presenter, while in MVVM, the view model does not have a reference to the view.

• MVVM allows for easier testing as the view mode...read more

Repository pattern is a design pattern that separates data access logic from business logic.

• It provides a way to access data without exposing the underlying database or data storage technology.

• It helps in achieving separation of concerns and makes the code more modular and testable.

• It involves creating a repository interface that defines the operations that can be performed on the data and a concrete implementation of the repository that interacts with the data storage techno...read more

Design a Book Management System for organizing and tracking books.

• Create a database to store book information such as title, author, genre, and availability status

• Implement a user interface for users to search, borrow, return, and reserve books

• Include features like notifications for due dates, book recommendations, and user reviews

Design patterns are reusable solutions to common problems in software design, while SOLID principles are guidelines for writing maintainable and scalable code.

• Design patterns help in organizing code, improving code reusability, and making code more maintainable.

• Examples of design patterns include Singleton, Factory, Observer, and Strategy.

• SOLID principles consist of Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, and Dependency Inversion.

• These ...read more

Snake game is a classic arcade game where a player controls a snake to eat food and grow longer while avoiding collisions with walls and itself.

• Create a grid-based game board where the snake can move in four directions (up, down, left, right)

• Generate food randomly on the board for the snake to eat and grow in length

• Implement collision detection to check if the snake hits the walls or itself

• Update the game state continuously based on user input and game logic

• Keep track of the ...read more

MVC pattern is a software design pattern that separates an application into three main components: Model, View, and Controller.

• Model represents the data and business logic of the application.

• View represents the UI components of the application.

• Controller acts as an intermediary between Model and View, handling user input and updating the Model accordingly.

• Example: In a web application, the Model could be a database, the View could be the HTML/CSS for the user interface, and t...read more

A basic Google Doc editor designed using OOP principles.

• Create a Document class to represent the Google Doc

• Include methods for editing text, adding images, and formatting

• Use classes like Text, Image, and FormattingOptions for different elements

• Implement features like undo/redo functionality and collaboration tools

Design patterns are reusable solutions to common problems in software design.

• Design patterns help in creating maintainable and scalable code.

• Examples include Singleton, Factory, Observer, and Strategy patterns.

• Each design pattern has a specific purpose and can be applied in different scenarios.

Singleton pattern ensures a class has only one instance, while observer pattern allows multiple objects to listen and react to changes in a subject.

• Singleton pattern involves a private constructor, a static method to access the instance, and a static variable to hold the instance.

• Observer pattern involves a subject that maintains a list of observers, and notifies them of any state changes.

• Example of singleton pattern: DatabaseConnection class with a private constructor, getIn...read more

Java design patterns are reusable solutions to common problems encountered in software design.

• Java design patterns help in creating flexible, reusable, and maintainable code.

• Examples of Java design patterns include Singleton, Factory, Observer, and Strategy.

• Design patterns can be categorized into three groups: creational, structural, and behavioral.

One of the most commonly used design patterns in JavaScript is the Module pattern.

• Encapsulates code into a single object, providing a way to create private and public methods and variables

• Helps in organizing code, reducing global scope pollution, and promoting reusability

• Example: var Module = (function() { var privateVar = 'private'; return { publicMethod: function() { console.log(privateVar); } }; })();

Design patterns are reusable solutions to common software design problems.

• Design patterns provide a common language for developers to communicate about software design.

• They can improve code quality, maintainability, and scalability.

• Examples of design patterns include Singleton, Factory, and Observer.

• Implementation involves applying the pattern to a specific problem in a software system.

• Design patterns can be implemented in various programming languages and frameworks.

Design principles are guidelines for designing software solutions, while design patterns are reusable solutions to common design problems.

• Design principles are high-level guidelines that help in designing software solutions that are scalable, maintainable, and efficient.

• Design patterns are reusable solutions to common design problems that have been proven to be effective in various scenarios.

• Examples of design principles include SOLID principles, DRY (Don't Repeat Yourself), ...read more

Microservices are a software architectural style that structures an application as a collection of loosely coupled services.

• Each service is self-contained and can be developed, deployed, and scaled independently.

• Communication between services typically occurs over lightweight protocols like HTTP or messaging queues.

• Microservices allow for greater flexibility, scalability, and resilience compared to monolithic architectures.

• Examples of microservices patterns include API Gatewa...read more

Design patterns are reusable solutions to common problems in software design. DI stands for Dependency Injection, a design pattern used to inject dependencies into a class.

• Design patterns are best practices for solving common software design problems.

• DI is a design pattern where dependencies are injected into a class rather than created within the class.

• Examples of design patterns include Singleton, Factory, and Observer.

• Dependency Injection helps improve code maintainability...read more

Factory pattern is used to create objects without exposing the instantiation logic to the client, while Singleton pattern ensures a class has only one instance and provides a global point of access to it.

• Factory pattern is used to create objects based on a common interface, without specifying the exact class of the object being created.

• Singleton pattern restricts the instantiation of a class to one object, ensuring that all requests for the object return the same instance.

• Fac...read more

Builder pattern is a creational design pattern that separates the construction of a complex object from its representation.

• Separates the construction of a complex object from its representation

• Allows the same construction process to create different representations

• Helps in creating objects step by step

A Singleton class is a class that can only have one instance created at a time.

• Singleton classes are often used for managing resources that should only have one instance, such as a database connection.

• To implement a Singleton class, you typically make the constructor private and provide a static method to access the single instance.

• Example: Singleton class for logging system where only one instance of the logger is needed.

Designing Java classes for a news channel

• Create a NewsChannel class with attributes like name, location, and list of news articles

• Create a NewsArticle class with attributes like title, author, content, and publish date

• Implement methods in NewsChannel class to add, remove, and display news articles

LRU cache is a data structure that maintains a fixed-size cache, evicting the least recently used item when full.

• Use a doubly linked list to maintain the order of items based on their usage frequency

• Use a hash map to quickly access items in the cache

• When an item is accessed, move it to the front of the linked list to mark it as the most recently used

• When adding a new item and the cache is full, remove the least recently used item from the end of the linked list

Builder design pattern is a creational design pattern used to construct complex objects step by step.

• Builder pattern separates the construction of a complex object from its representation.

• It allows the same construction process to create different representations of the object.

• Useful when there are multiple ways to construct an object or when the object creation process is complex.

• Example: StringBuilder in Java allows you to build strings by appending characters or other stri...read more

Thread safe singleton can be implemented using double-checked locking or synchronized block.

• Use double-checked locking to ensure only one instance is created.

• Use synchronized block to make sure only one thread can access the creation of instance at a time.

• Example: public class ThreadSafeSingleton { private static volatile ThreadSafeSingleton instance; private ThreadSafeSingleton(){} public static ThreadSafeSingleton getInstance() { if (instance == null) { synchronized (Thread...read more

Design patterns are reusable solutions to common software problems. Singleton is a design pattern that restricts the instantiation of a class to one object.

• Design patterns are proven solutions to recurring software problems

• Singleton pattern ensures only one instance of a class is created

• Singleton pattern is useful in scenarios where only one instance of a class is required

• Other design patterns include Factory, Observer, and Decorator patterns

SAGA design pattern is used for managing long-lived transactions in distributed systems.

• SAGA pattern breaks down a long transaction into a series of smaller, more manageable steps.

• Each step in the SAGA pattern is a separate transaction that can be rolled back if needed.

• SAGA pattern ensures that the overall transaction is eventually consistent.

• Examples of SAGA pattern implementation include using compensating transactions or event-driven architecture.

Saga pattern is used to maintain data consistency in distributed systems by breaking down transactions into smaller, independent steps.

• Saga pattern involves breaking down a transaction into a series of smaller steps or sub-transactions.

• Each step in the saga is independent and can be rolled back if needed.

• If a step fails, compensating transactions can be executed to undo the changes made by previous steps.

• Saga pattern helps in maintaining data consistency in distributed system...read more

Singleton ensures a class has only one instance, while Abstract Factory provides an interface for creating families of related objects.

• Singleton pattern restricts the instantiation of a class to one object, ensuring there is only one instance of the class.

• Abstract Factory pattern provides an interface to create families of related or dependent objects without specifying their concrete classes.

• Singleton pattern can be implemented using a private constructor, static method to a...read more

Design patterns are reusable solutions to common software problems.

• Creational patterns: Singleton, Factory, Abstract Factory

• Structural patterns: Adapter, Decorator, Facade

• Behavioral patterns: Observer, Strategy, Command

• Architectural patterns: Model-View-Controller, Model-View-ViewModel

• Concurrency patterns: Thread Pool, Producer-Consumer

• Examples: Singleton ensures only one instance of a class exists, Factory creates objects without exposing the instantiation logic, Observer al...read more

Singleton design pattern ensures only one instance of a class is created and provides a global point of access to it.

• Create a private constructor to prevent direct instantiation of the class

• Create a private static instance of the class

• Create a public static method to access the instance

• Ensure thread safety by using synchronized keyword or static initialization block

• Example: Database connection manager

There are three types of controllers in MVC: 1. View Controller 2. Action Controller 3. Partial View Controller

• View Controller handles user interface and displays data

• Action Controller handles user input and performs actions

• Partial View Controller handles reusable UI components

• Examples: HomeController, AccountController, ProductController

Singleton pattern restricts the instantiation of a class to a single instance and provides a global point of access to it.

• Used when only one instance of a class is required throughout the system

• Ensures that the instance is created only once and provides a global point of access to it

• Commonly used in logging, configuration settings, and database connections

• Implemented by making the constructor private and providing a static method to access the instance

• Example: Java's Runtime ...read more

Design a lift system using OOP principles

• Create classes for Lift, Floor, Button, and Person

• Use inheritance and polymorphism to model different types of lifts and buttons

• Implement methods for moving the lift, opening/closing doors, and handling button presses

• Use encapsulation to protect the internal state of the lift system

• Consider using design patterns like Observer for tracking state changes

MVVM is a software architectural pattern that separates the user interface from the business logic and data.

• MVVM stands for Model-View-ViewModel

• Model represents the data and business logic

• View represents the user interface

• ViewModel acts as a mediator between the Model and View

• ViewModel exposes data and commands to the View

• MVVM promotes separation of concerns and testability

• Example: Using MVVM in a mobile app, the ViewModel would handle data retrieval and manipulation, while t...read more

Factory design 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.

• Factory design pattern involves creating an interface or abstract class for creating objects.

• Subclasses implement the interface to create specific types of objects.

• It allows the client code to create objects without specifying the exact class of object that will be created.

• Example: Factory metho...read more

Command factory pattern is a design pattern that creates objects based on the command type.

• It is used to encapsulate the creation of command objects.

• It provides a way to decouple the client from the command objects.

• It can be used in applications that require dynamic creation of commands.

• Example: A remote control for a TV that creates different commands based on user input.

Microservices are a software architectural style that structures an application as a collection of loosely coupled services.

• Microservices break down a large application into smaller, independent services that can be developed, deployed, and scaled independently.

• Common design patterns used in microservices architecture include Service Registry, Circuit Breaker, API Gateway, and Event Sourcing.

• Service Registry pattern helps services locate and communicate with each other.

• Circui...read more

The observer pattern was not used in the app due to performance concerns and complexity.

• The observer pattern can lead to performance issues in apps with a large number of observers.

• Direct method calls can be more efficient than using the observer pattern.

• The app may not have complex event handling requirements that warrant the use of the observer pattern.

Design a system similar to cars24, discussing components and design patterns.

• Components: User interface, database, search engine, recommendation engine, payment gateway

• Design pattern: Model-View-Controller (MVC)

• User interface: Allow users to search for cars, view car details, and make purchases

• Database: Store car information, user details, and transaction history

• Search engine: Enable users to search for cars based on various criteria

• Recommendation engine: Suggest cars based o...read more

Repository pattern is a design pattern that separates data access logic from business logic in an application.

• It helps in achieving separation of concerns by abstracting the data access logic into a separate layer.

• It provides a way to centralize data access logic and reuse it across the application.

• It typically involves creating interfaces for data access operations and implementing them in concrete classes.

• Example: In a web application, the repository pattern can be used to ...read more

System design patterns are reusable solutions to common problems in software design.

• System design patterns help in organizing code, improving scalability, and enhancing maintainability.

• Examples include MVC (Model-View-Controller), Singleton, Factory, Observer, and Dependency Injection.

• Each pattern has its own set of rules and best practices to follow for implementation.

Solid principles and design patterns are essential for writing maintainable and scalable code.

• SOLID principles are a set of five principles that help in designing maintainable and scalable software.

• Design patterns are reusable solutions to common software design problems.

• SOLID principles include Single Responsibility Principle, Open-Closed Principle, Liskov Substitution Principle, Interface Segregation Principle, and Dependency Inversion Principle.

• Design patterns include Crea...read more

Snake game involves controlling a snake to eat food and grow in size without hitting walls or itself.

• Create a grid system to represent the game board

• Implement logic for snake movement and growth

• Generate food randomly on the board for the snake to eat

• Handle collision detection for walls and snake body

• Keep track of score and game over conditions

MVC design pattern separates an application into three main components: Model, View, and Controller.

• Model represents the data and business logic of the application

• View is responsible for displaying the data to the user

• Controller acts as an intermediary between Model and View, handling user input and updating the Model accordingly

Observer design pattern is a behavioral design pattern that allows objects to subscribe and receive updates from a subject.

• It is used to establish a one-to-many dependency between objects.

• The subject maintains a list of observers and notifies them of any state changes.

• Observers can be added or removed dynamically.

• It promotes loose coupling between objects.

• Example: A weather station broadcasts weather updates to multiple display devices.

I will implement microservice architecture using containerization and API gateway pattern.

• Identify the bounded contexts and break down the monolith into smaller services

• Use containerization tools like Docker and Kubernetes for deployment and scaling

• Implement API gateway pattern to manage the communication between services

• Use service discovery tools like Consul or Eureka for service registration and discovery

• Implement fault tolerance and resilience patterns like circuit breake...read more

Dependency Injection is a design pattern where components are given their dependencies rather than creating them internally.

• Allows for easier testing by mocking dependencies

• Promotes loose coupling between components

• Improves code reusability and maintainability

• Example: Constructor injection, Setter injection, Interface injection

Design patterns are reusable solutions to common problems in software design. Singleton ensures a class has only one instance, while factory creates objects without specifying the exact class.

• Design patterns are best practices for solving common software design problems.

• Singleton pattern ensures a class has only one instance and provides a global point of access to it.

• Factory pattern creates objects without specifying the exact class to be instantiated.

• Examples: Singleton - D...read more

Singleton pattern ensures only one instance of a class is created and provides a global point of access to it.

• Use lazy initialization to create the instance only when needed.

• Use synchronized keyword to make the getInstance() method thread-safe.

• Consider using double-checked locking for better performance.

• Use enum to implement singleton pattern as it is inherently thread-safe.

Singleton design pattern ensures a class has only one instance and provides a global point of access to it.

• Used when only one instance of a class is needed throughout the system

• Provides a global access point to the instance

• Implemented by creating a static method to return the same instance each time it is called