10+ Backend Engineer Lead Interview Questions and Answers

Create an ArrayList and add 5 numbers to it.

• Declare an ArrayList variable and initialize it

• Use the add() method to add numbers to the ArrayList

• Numbers can be of any data type (int, double, etc.)

• Example: ArrayList<Integer> numbers = new ArrayList<>(); numbers.add(1);

• Make sure to import the ArrayList class

HashMap in Java is internally stored as an array of linked lists.

• HashMap uses hashing to store key-value pairs

• Each key is hashed to an index in the array

• If there are collisions, a linked list is used to store multiple values at the same index

• The default initial capacity of HashMap is 16 and load factor is 0.75

• HashMap is not thread-safe and requires synchronization for concurrent access

Implement Push Function for Queue using Array or ArrayList

• Create a function that takes an array or ArrayList and a string as input

• Add the string to the end of the array or ArrayList

• Return the updated array or ArrayList

Explanation of OOPS pillars with real-life examples

• Abstraction: Hiding implementation details, e.g. using a TV remote without knowing how it works

• Encapsulation: Grouping related data and functions, e.g. a car's engine and transmission

• Inheritance: Creating new classes from existing ones, e.g. a sports car class inheriting from a car class

• Polymorphism: Using a single interface to represent multiple classes, e.g. a shape class with different subclasses for circle, square, etc.

Overloading and overriding are two concepts in object-oriented programming that allow methods to have multiple implementations.

• Overloading is when a class has multiple methods with the same name but different parameters.

• Overriding is when a subclass provides a different implementation of a method that is already defined in its superclass.

• Overloading is resolved at compile-time while overriding is resolved at runtime.

• Example of overloading: public void print(int x) and public ...read more

Designing database tables for a ticket booking platform like BookMyShow, focusing on relationships and data integrity.

• Users table: Stores user information (user_id, name, email, password).

• Movies table: Contains movie details (movie_id, title, genre, duration, rating).

• Theaters table: Holds theater information (theater_id, name, location, capacity).

• Shows table: Links movies and theaters (show_id, movie_id, theater_id, show_time, available_seats).

• Bookings table: Records user boo...read more

The department with the maximum number of students needs to be found.

• Join the Department and Student tables on the dept_id column

• Group the data by department

• Count the number of students in each department

• Find the department with the maximum count

Laravel request life cycle involves several stages from receiving the request to sending the response.

• The request is received by the web server and passed to the PHP engine.

• The kernel receives the request and sends it to the router.

• The router matches the request to the appropriate route and sends it to the controller.

• The controller processes the request and returns a response.

• The response is sent back through the middleware and finally to the client.

Print Fibonacci series

• Fibonacci series is a sequence of numbers where each number is the sum of the two preceding ones

• The first two numbers of the series are always 0 and 1

• The series can be generated using a loop or recursion

• Example: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181

SQL joins combine rows from two or more tables based on related columns, enabling complex queries and data retrieval.

• INNER JOIN: Returns records with matching values in both tables. Example: SELECT * FROM Orders INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID;

• LEFT JOIN: Returns all records from the left table and matched records from the right table. Example: SELECT * FROM Customers LEFT JOIN Orders ON Customers.CustomerID = Orders.CustomerID;

• RIGHT JOIN: Retu...read more

SQL databases are suitable for structured data and complex queries, while NoSQL databases are better for unstructured data and high scalability.

• Use SQL databases when data has a fixed schema and relationships between entities are well-defined.

• Use NoSQL databases when data is unstructured or semi-structured, and when high scalability and performance are required.

• SQL databases are better for complex queries involving multiple tables and joins.

• NoSQL databases are suitable for ha...read more

Caching is a technique used to store frequently accessed data in a temporary storage for faster retrieval.

• Caching improves performance by reducing the need to fetch data from the original source.

• It involves storing data in a cache, which is a high-speed storage system closer to the user or application.

• When a request is made for data, the cache is checked first, and if the data is found, it is returned quickly.

• If the data is not in the cache, it is fetched from the original so...read more

Merge overlapping time intervals in an array of intervals.

• Sort the intervals based on the start time.

• Iterate through the intervals and merge overlapping intervals.

• Return the merged intervals.