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 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

I implemented various features including X, Y, and Z.

• Implemented feature X which improved system performance by 20%

• Developed feature Y which allowed for real-time data analysis

• Added feature Z which improved user experience by simplifying the interface

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

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

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

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.

Invoice sequence numbers can be generated using a combination of prefix, date, and a unique number.

• Prefix can be a combination of letters or numbers to identify the type of invoice

• Date can be added to the prefix to make it more specific

• A unique number can be generated using a counter or random number generator

• The combination of prefix, date, and unique number can be formatted to create the final invoice number

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

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.