200+ Lead Software Engineer Interview Questions and Answers

Interfaces are contracts that define a set of methods that a class must implement. They help achieve abstraction and loose coupling.

• Interfaces provide a way to achieve abstraction and loose coupling in code.

• They define a set of methods that a class must implement, but not how they are implemented.

• Classes can implement multiple interfaces, allowing for greater flexibility and reusability.

• Interfaces are commonly used in dependency injection and mocking frameworks.

• Example: The J...read more

The first round focused on technical definitions in programming and testing methodologies.

• Questions included definitions of OOP concepts like inheritance and polymorphism.

• Technical terms such as 'unit testing' and 'integration testing' were discussed.

• Examples of programming languages like Python and Java were used to illustrate concepts.

• The interviewer asked about the differences between functional and non-functional testing.

A View Model in Android is a class that stores and manages UI-related data in a lifecycle-conscious way.

• View Model helps to separate the UI data from the UI controller logic.

• It survives configuration changes and can be shared between fragments or activities.

• Example: ViewModel class in Android Architecture Components.

Web application is a complete software program accessed through a web browser, while web API application is a set of programming instructions that allow communication between different software systems.

• Web application is a complete software program accessed through a web browser

• Web API application is a set of programming instructions that allow communication between different software systems

• Web application provides a user interface for the end-user to interact with the softw...read more

CSV stands for comma-separated values, VP is validation protocol. 21CFR part 11 and EU annex 11 are regulations for electronic records and signatures in the US and EU. Gamp5 is a guideline for validation of computerized systems in the pharmaceutical industry.

• CSV is a file format used for storing tabular data in plain text, with each line representing a data record and each record separated by commas.

• VP is a validation protocol used to ensure that a system or process meets pre...read more

Encryption is the process of converting plain text into a coded message to prevent unauthorized access.

• Encryption uses an algorithm and a key to convert plain text into ciphertext.

• Decryption uses the same algorithm and key to convert ciphertext back into plain text.

• Common encryption algorithms include AES, RSA, and Blowfish.

• Encryption is used to protect sensitive data such as passwords, credit card numbers, and personal information.

• Encryption can be done at different levels s...read more

C++ OOP concepts include encapsulation, inheritance, polymorphism, and abstraction, enabling modular and reusable code design.

• Encapsulation: Bundling data and methods that operate on the data within a single unit (class). Example: class Car { private: int speed; public: void setSpeed(int s) { speed = s; } };

• Inheritance: Mechanism to create a new class from an existing class, inheriting attributes and behaviors. Example: class Vehicle { }; class Car : public Vehicle { };

• Polymo...read more

Caching system improves performance by storing frequently accessed data in memory.

• Caching reduces the need to fetch data from the server, improving load times.

• Common caching systems include Redis, Memcached, and browser caching.

• Caching can be implemented at various levels such as browser, CDN, and server-side.

• Examples of cached data in frontend include images, CSS files, and API responses.

Design system is crucial for consistency, efficiency, and scalability in software development.

• Ensures consistency in UI/UX across products and platforms

• Promotes reusability of components and patterns

• Facilitates collaboration between design and development teams

• Increases efficiency by streamlining the design and development process

• Helps in scaling the product by providing a structured framework for growth

Automated a login functionality test case for a web application to ensure user authentication works correctly.

• Test Case: Verify successful login with valid credentials.

• Steps: Navigate to the login page, enter username and password, click 'Login'.

• Expected Result: User is redirected to the dashboard page.

• Tools Used: Selenium WebDriver for automation.

• Validation: Check for the presence of a logout button on the dashboard.

Employ strategies like rate limiting, authentication, and data validation to optimize and secure APIs effectively.

• Implement rate limiting to control the number of requests a user can make, preventing abuse. For example, allow 100 requests per hour.

• Use authentication mechanisms like OAuth 2.0 to ensure that only authorized users can access the API.

• Validate input data rigorously to prevent injection attacks. For instance, use libraries that sanitize inputs.

• Employ HTTPS to encry...read more

Implementing a real-time chat feature using WebSockets and Redis pub/sub

• Used WebSockets to establish a persistent connection between clients and server

• Utilized Redis pub/sub for broadcasting messages to multiple clients in real-time

• Implemented message queuing to handle high traffic and ensure message delivery

Pure Components in React JS are components that do not re-render unless their props have changed.

• Pure Components extend React.Component and implement shouldComponentUpdate method for shallow comparison of props and state.

• Pure Components are more efficient than regular components as they prevent unnecessary re-renders.

• Example: class MyComponent extends React.PureComponent { // component code here }

The Standard Template Library (STL) in C++ provides a collection of template classes and functions for data structures and algorithms.

• Containers: STL includes various container types like vector, list, and map, which store collections of data. Example: std::vector<int> numbers;

• Algorithms: STL provides a range of algorithms such as sort, search, and transform that can be applied to containers. Example: std::sort(numbers.begin(), numbers.end());

• Iterators: STL uses iterators to ...read more

REST endpoints for a ticket booking system

• GET /events - get list of available events

• GET /events/{id} - get details of a specific event

• POST /events/{id}/tickets - book tickets for an event

• GET /bookings - get list of all bookings

• GET /bookings/{id} - get details of a specific booking

• PUT /bookings/{id} - update a booking

• DELETE /bookings/{id} - cancel a booking

Fail safe focuses on ensuring system stability and preventing catastrophic failures, while fail fast prioritizes quick detection and response to errors.

• Fail safe is about designing systems to minimize the impact of failures and ensure stability.

• Fail fast is about quickly detecting and responding to errors to prevent further issues.

• Fail safe often involves redundancy and error checking mechanisms to prevent catastrophic failures.

• Fail fast encourages rapid feedback loops and ea...read more

Design a shopping cart system supporting multiple products and discount coupons.

• User can add/remove multiple products to/from the cart.

• Each product has attributes: ID, name, price, quantity.

• Discount coupons can be applied at checkout, affecting total price.

• Coupons may have conditions, e.g., minimum purchase amount or product categories.

• Implement a total price calculation method considering discounts.

• Example: A cart with 3 items totaling $100, applying a $10 coupon results in ...read more

Print only values from a nested JS object

• Use Object.values() to get an array of values

• Recursively iterate through nested objects

• Filter out non-object values before iterating

Check if two strings are anagrams of each other

• Create a character count array for both strings

• Compare the character count arrays

• If they are equal, the strings are anagrams

CI/CD pipelines, frontend architecture, and e2e testing libraries are crucial aspects of software development.

• CI/CD pipelines automate the process of testing and deploying code changes, ensuring faster and more reliable software delivery.

• Architecting the frontend involves designing the structure, components, and interactions of the user interface to ensure scalability and maintainability.

• E2E testing libraries like Selenium or Cypress are used to simulate user interactions and...read more

React lifecycle methods include componentDidMount, componentDidUpdate, componentWillUnmount, etc.

• componentDidMount - called after component is rendered for the first time

• componentDidUpdate - called after component's state or props change

• componentWillUnmount - called before component is removed from the DOM

Discussing OOP principles and their application in software design and development.

• Encapsulation: Hiding internal state, e.g., using private variables in a class.

• Inheritance: Creating a base class and extending it, e.g., a 'Vehicle' class with 'Car' and 'Bike' subclasses.

• Polymorphism: Method overriding, e.g., a 'draw' method in a 'Shape' class that is implemented differently in 'Circle' and 'Square'.

• Abstraction: Using abstract classes/interfaces to define common behaviors, e....read more

Deploying service in production server involves building the application, configuring the server, and monitoring performance.

• Build the application code into a deployable package (e.g. JAR file for Java applications)

• Configure the production server with necessary dependencies and environment variables

• Deploy the application package to the server using tools like Docker, Kubernetes, or manual deployment scripts

• Monitor the performance of the deployed service using monitoring tools...read more

Designing a wallet payment system like Paytm involves key components for transactions, security, and user management.

• User Authentication: Secure login via email, phone number, or biometrics.

• Wallet Management: Users can add, withdraw, and transfer funds.

• Transaction Processing: Real-time processing of payments and refunds.

• Merchant Integration: APIs for merchants to accept payments seamlessly.

• Security Measures: Encryption, two-factor authentication, and fraud detection.

• User Inte...read more

SSL is a security protocol used to establish an encrypted link between a web server and a browser.

• SSL stands for Secure Sockets Layer.

• It is used to protect sensitive information such as login credentials, credit card details, etc.

• SSL uses encryption to ensure that data transmitted between the server and browser cannot be intercepted by third parties.

• It is essential for e-commerce websites, online banking, and any website that handles sensitive information.

• SSL has been replace...read more

Breaking down a monolith into microservices involves identifying bounded contexts, decoupling components, and implementing communication mechanisms.

• Identify bounded contexts within the monolith to define the boundaries of microservices.

• Decouple components by extracting them into separate services with well-defined interfaces.

• Implement communication mechanisms such as RESTful APIs or message queues to enable interaction between microservices.

• Use containerization technologies l...read more

Spring Boot dependency injection is a design pattern where objects are passed their dependencies rather than creating them internally.

• In Spring Boot, dependency injection is achieved through the use of @Autowired annotation.

• It helps in achieving loose coupling between classes and promotes easier testing and maintenance.

• Example: @Autowired private UserService userService; // Injecting UserService dependency