Principal Software Engineer

70+ Principal Software Engineer Interview Questions and Answers

Updated 16 Dec 2024

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Q1. Codng question:For the given stream of integers, calculate the avg,print top 10 elements and bottom 10 elements. It was not clearly mentioned on the problem. After poking more on the problem only provided the d...

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Ans.

Calculate average, top 10 and bottom 10 elements of a given stream of integers.

  • Create a variable to store the sum of integers and another variable to store the count of integers.

  • Use a loop to read the integers from the stream and update the sum and count variables.

  • Calculate the average by dividing the sum by the count.

  • Sort the integers in ascending order and print the first 10 elements for bottom 10.

  • Sort the integers in descending order and print the first 10 elements for top...read more

Q2. Implement Linked list with add, display, insert at end and delete operations.

Ans.

Implementation of Linked List with add, display, insert at end and delete operations.

  • Create a Node class with data and next pointer

  • Create a LinkedList class with head pointer

  • Add method to add a new node at the end of the list

  • Display method to print all nodes in the list

  • Insert at end method to insert a new node at the end of the list

  • Delete method to delete a node from the list

Principal Software Engineer Interview Questions and Answers for Freshers

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Q3. Predict Output based on whether static variables can be accessed from non-static method

Ans.

Static variables can be accessed from non-static methods using an object reference or by making the variable non-static.

  • Static variables can be accessed from non-static methods by creating an object of the class containing the static variable.

  • Alternatively, the static variable can be made non-static to be accessed directly from a non-static method.

  • Attempting to access a static variable directly from a non-static method will result in a compilation error.

Q4. Why looking for change ? What kind of work is there in qualys?

Ans.

I am looking for change to explore new challenges and opportunities. Qualys offers a variety of work in cybersecurity and cloud security.

  • Seeking new challenges and opportunities to grow professionally

  • Interested in cybersecurity and cloud security

  • Excited about the diverse range of projects at Qualys

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Q5. String a = "Something" a.concat(" New") What will be garbage collected?

Ans.

Only the original string 'Something' will be garbage collected.

  • The concat method in Java does not modify the original string, but instead returns a new string with the concatenated value.

  • In this case, 'a' remains as 'Something' and a new string 'Something New' is created, but not assigned to any variable.

  • Since the new string is not stored in any variable, it will not be garbage collected.

Q6. String a = "Something" String b = new String("Something") How many object created?

Ans.

Two objects created - one in the string pool and one in the heap.

  • String 'a' is created in the string pool, while String 'b' is created in the heap.

  • String pool is a special area in the heap memory where strings are stored to increase reusability and save memory.

  • Using 'new' keyword always creates a new object in the heap, even if the content is the same as an existing string in the pool.

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Q7. When to Use Array and Hashset and Hashmap

Ans.

Arrays are used for ordered collections, HashSet for unique elements, and HashMap for key-value pairs.

  • Use arrays when you need to store elements in a specific order and access them by index.

  • Use HashSet when you need to store unique elements and do not care about the order.

  • Use HashMap when you need to store key-value pairs and quickly retrieve values based on keys.

Q8. Find the longest increasing decreasing subsequence in an array. hint- DP question

Ans.

Use dynamic programming to find the longest increasing decreasing subsequence in an array.

  • Use dynamic programming to keep track of the length of the longest increasing subsequence ending at each index.

  • Similarly, keep track of the length of the longest decreasing subsequence starting at each index.

  • Combine the two to find the longest increasing decreasing subsequence.

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Q9. Two stack implementation with one single array with no extra space

Ans.

Implement two stacks using a single array without extra space.

  • Divide the array into two halves and use one half for each stack.

  • Keep track of the top of each stack separately.

  • Handle stack overflow and underflow conditions.

  • Example: Implementing two stacks for undo and redo operations in a text editor.

Q10. What are the features of Date and Time API in Java 8

Ans.

Java 8 Date and Time API provides improved date and time handling capabilities.

  • Introduction of new classes like LocalDate, LocalTime, LocalDateTime, ZonedDateTime, OffsetTime, OffsetDateTime, and Instant for better date and time manipulation

  • Support for time zones and offsets

  • Ability to perform date and time calculations easily

  • Enhanced formatting and parsing capabilities

  • Integration with existing date and time classes like java.util.Date and java.util.Calendar

Q11. Write code two merge and remove duplicates from two sorted arrays with any Collections

Ans.

Merge and remove duplicates from two sorted arrays without using Collections

  • Use two pointers to iterate through both arrays simultaneously

  • Compare elements at each pointer and add the smaller one to the result array

  • Skip duplicates by checking if the current element is equal to the previous element

Q12. Ower design is superior to your why didn't you follow l

Ans.

I chose a different design approach based on specific project requirements and constraints.

  • Considered project requirements and constraints when deciding on design approach

  • Different designs may have different trade-offs and considerations

  • Example: Chose a design that prioritized scalability over simplicity due to anticipated growth in user base

Q13. high level system design for a movie booking app

Ans.

A movie booking app system design involves user authentication, movie selection, seat reservation, payment processing, and booking confirmation.

  • User authentication: Implement login/signup functionality for users.

  • Movie selection: Display list of movies with details like showtimes, ratings, and genres.

  • Seat reservation: Allow users to select seats for chosen movie showtime.

  • Payment processing: Integrate payment gateway for secure transactions.

  • Booking confirmation: Send confirmati...read more

Q14. How do you handle critical application incident?

Ans.

I handle critical application incidents by following a structured incident response process.

  • Quickly assess the severity and impact of the incident

  • Notify relevant stakeholders and form an incident response team

  • Identify the root cause of the issue and implement a temporary fix if needed

  • Communicate updates and progress to stakeholders regularly

  • Conduct a post-incident review to learn from the incident and prevent future occurrences

Q15. What's the use of 'Volatile' keyword in C#?

Ans.

The 'Volatile' keyword in C# is used to indicate that a field might be modified by multiple threads that are executing at the same time.

  • Ensures that any read or write operation on the variable is done directly from the main memory and not from the CPU cache.

  • Useful when working with multithreaded applications to prevent unexpected behavior due to caching.

  • Example: 'volatile int count = 0;'

Q16. What do you know about Oracle?

Ans.

Oracle is a multinational computer technology corporation that specializes in developing and marketing database software and technology.

  • Oracle is known for its flagship product, the Oracle Database, which is widely used in enterprise applications.

  • It also offers a range of other software products, including middleware, application development tools, and cloud services.

  • Oracle has a strong presence in the enterprise market and is a major competitor to other database vendors like...read more

Q17. What is the regression testing?

Ans.

Regression testing is the process of retesting modified software to ensure that previously working functionalities still work as expected.

  • Regression testing is performed after making changes to software to identify any new defects or issues introduced.

  • It helps ensure that existing functionalities are not affected by the changes made.

  • Regression testing can be done manually or using automated testing tools.

  • It involves re-executing test cases that cover the affected areas of the...read more

Q18. Write code to emulate Producer/Consumer Problem

Ans.

Emulate Producer/Consumer Problem using code

  • Create a shared buffer between producer and consumer

  • Use synchronization mechanisms like mutex or semaphore to control access to the buffer

  • Implement producer and consumer functions to add and remove items from the buffer respectively

Q19. joins and merge in sql and python

Ans.

Joins and merges are used to combine data from multiple tables in SQL and Python.

  • Joins in SQL are used to combine rows from two or more tables based on a related column between them.

  • Types of joins in SQL include INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.

  • Merging in Python is done using the pandas library, where two DataFrames are combined based on a common column.

  • Example: SQL - SELECT * FROM table1 INNER JOIN table2 ON table1.id = table2.id

  • Example: Python - merged_df = ...read more

Q20. How to redirect api call from version1 to version2

Ans.

To redirect api call from version1 to version2, update the endpoint in the code or use a reverse proxy.

  • Update the endpoint in the code to point to version2

  • Use a reverse proxy like NGINX to redirect calls from version1 to version2

  • Implement a routing mechanism to handle the redirection

Q21. sql query to find 2nd largest salary

Ans.

Use SQL query with ORDER BY and LIMIT to find 2nd largest salary.

  • Use ORDER BY clause to sort salaries in descending order

  • Use LIMIT 1,1 to get the second row after skipping the first row

Q22. What do you like about Oracle?

Ans.

I appreciate Oracle's robust and reliable software solutions.

  • Oracle's software is known for its scalability and performance.

  • Their database management system is widely used and trusted by many organizations.

  • Oracle's cloud offerings provide a comprehensive suite of services for businesses.

  • Their commitment to innovation and staying ahead of industry trends is impressive.

Q23. how do you manage deployment process?

Ans.

I use a combination of automation tools and manual checks to ensure smooth deployment process.

  • Automate repetitive tasks using tools like Jenkins or Ansible

  • Perform manual checks to ensure quality and avoid errors

  • Use version control to track changes and roll back if necessary

  • Collaborate with development and operations teams to ensure smooth deployment

  • Monitor system performance and troubleshoot issues as they arise

Q24. What is difference between deadlock and blocking

Ans.

Deadlock is a situation where two or more processes are unable to proceed because each is waiting for the other to release a resource, while blocking is when a process is waiting for a resource to become available.

  • Deadlock involves multiple processes waiting indefinitely for each other to release resources

  • Blocking is when a process is waiting for a resource to become available before it can proceed

  • Deadlock can occur in multi-threaded applications, while blocking can occur in ...read more

Q25. What is the use of pretty in JavaScript

Ans.

The pretty function in JavaScript is used to format and display data in a more visually appealing way.

  • Pretty function is used to format JSON data for better readability.

  • It can be used to display data in a structured and organized manner.

  • Pretty function is commonly used in debugging to make output easier to read.

Q26. When will you use private constructor ?

Ans.

Private constructors are used to prevent instantiation of a class from outside the class itself.

  • Private constructors are used in classes that should not be instantiated directly by external code.

  • They are often used in classes that contain only static methods or properties.

  • Private constructors can also be used in singleton design pattern to ensure only one instance of a class is created.

Q27. how to sort collections using comparator

Ans.

Sorting collections using comparator

  • Implement the Comparator interface

  • Override the compare() method to define sorting logic

  • Pass the comparator object to the sort() method of the collection

  • Example: Arrays.sort(arr, new MyComparator())

Q28. Product of an array except self

Ans.

Calculate the product of all elements in an array except for the element itself.

  • Iterate through the array and calculate the product of all elements except the current element.

  • Use two separate arrays to store the product of elements to the left and right of the current element.

  • Multiply the corresponding elements from the left and right arrays to get the final result.

Q29. Write code to create a deadlock

Ans.

Creating a deadlock involves two or more threads waiting for each other to release a resource they need.

  • Create two threads, each trying to lock two resources in a different order

  • Ensure that one thread locks resource A first and then tries to lock resource B, while the other thread locks resource B first and then tries to lock resource A

  • This will result in a situation where each thread is waiting for the other to release the resource it needs, causing a deadlock

Q30. Write code to implement LRU Cache

Ans.

Implement LRU Cache using a data structure like LinkedHashMap in Java

  • Use LinkedHashMap to maintain insertion order

  • Override removeEldestEntry method to limit cache size

  • Update the access order on get and put operations

Q31. How collections works internally?

Ans.

Collections in programming languages are data structures that store and organize multiple elements.

  • Collections can be implemented using various data structures such as arrays, linked lists, hash tables, and trees.

  • They provide methods for adding, removing, and accessing elements efficiently.

  • Examples of collections in Java include ArrayList, LinkedList, HashMap, and TreeSet.

Q32. how to sort an array and complexity

Ans.

Sorting an array of strings using a sorting algorithm like quicksort or mergesort.

  • Use a sorting algorithm like quicksort or mergesort to sort the array of strings.

  • Ensure the sorting algorithm is efficient and has a time complexity of O(n log n).

  • Consider the space complexity of the sorting algorithm as well.

Q33. What are ui automation script

Ans.

UI automation scripts are programs that simulate user interactions with a software application's graphical user interface.

  • UI automation scripts are used to test the functionality and performance of software applications.

  • They can be written in various programming languages such as Java, Python, and C#.

  • UI automation scripts can simulate user actions such as clicking buttons, entering text, and navigating menus.

  • They can also be used to verify that the application's user interfac...read more

Q34. Difference between POJO and Bean

Ans.

POJO is a Plain Old Java Object with private fields and public getters/setters, while a Bean is a Java class with private fields and public zero-argument constructors.

  • POJO stands for Plain Old Java Object

  • POJO has private fields and public getters/setters

  • Bean is a Java class with private fields and public zero-argument constructors

  • Beans are usually used in Java EE frameworks like Spring for dependency injection

Q35. window functions in sql

Ans.

Window functions in SQL are used to perform calculations across a set of table rows related to the current row.

  • Window functions are used to calculate values based on a set of rows related to the current row

  • They can be used with aggregate functions like SUM, AVG, etc.

  • Common window functions include ROW_NUMBER, RANK, DENSE_RANK, LAG, LEAD, etc.

Q36. write data to external table

Ans.

To write data to an external table

  • Use SQL INSERT INTO statement to insert data into the external table

  • Make sure to specify the table name and column names in the INSERT INTO statement

  • Ensure that the data being inserted matches the data types of the columns in the external table

Q37. EXPLAIN current project application architecture.

Ans.

Current project application architecture is microservices-based with containerization using Docker and orchestration with Kubernetes.

  • Microservices architecture for scalability and flexibility

  • Containerization with Docker for easy deployment and management

  • Orchestration with Kubernetes for automated scaling and load balancing

Q38. Solid principal with example, Design pattern,

Ans.

Solid principle is a set of five design principles for creating maintainable software

  • Single Responsibility Principle - a class should have only one reason to change

  • Open/Closed Principle - classes should be open for extension but closed for modification

  • Liskov Substitution Principle - objects of a superclass should be replaceable with objects of its subclasses without affecting the program's correctness

  • Interface Segregation Principle - clients should not be forced to depend on ...read more

Q39. Write code to read a file

Ans.

Code to read a file in Java

  • Use FileReader and BufferedReader classes to read the file

  • Handle exceptions using try-catch blocks

  • Close the file after reading using close() method

Q40. Write code to start 5 threads

Ans.

Code to start 5 threads in Java

  • Create a class that implements the Runnable interface

  • Instantiate 5 objects of the class

  • Create 5 threads using the objects and start them

Q41. What are SOLID principles?

Ans.

SOLID principles are a set of five design principles that help make software designs more understandable, flexible, and maintainable.

  • S - Single Responsibility Principle: A class should have only one reason to change.

  • O - Open/Closed Principle: Software entities should be open for extension but closed for modification.

  • L - Liskov Substitution Principle: Objects of a superclass should be replaceable with objects of its subclasses without affecting the functionality.

  • I - Interface ...read more

Frequently asked in,

Q42. What is multi threading?

Ans.

Multi threading is a programming concept where multiple threads within a process execute concurrently, allowing for better performance and responsiveness.

  • Allows for parallel execution of tasks within a single process

  • Improves performance by utilizing multiple CPU cores

  • Can lead to synchronization issues if not handled properly

  • Examples include web servers handling multiple client requests simultaneously

Frequently asked in,

Q43. How application CICD works?

Ans.

CICD stands for Continuous Integration/Continuous Deployment, a process that automates the building, testing, and deployment of applications.

  • CICD involves automating the process of integrating code changes, testing them, and deploying them to production.

  • It typically includes stages like code commit, build, test, and deployment.

  • Tools like Jenkins, GitLab CI/CD, and CircleCI are commonly used for CICD pipelines.

  • CICD helps in ensuring that code changes are quickly and safely dep...read more

Q44. Explain about CI CD Pipeline

Ans.

CI/CD pipeline is a set of practices and tools that automate the process of building, testing, and deploying software.

  • CI/CD stands for Continuous Integration/Continuous Deployment

  • It involves automating the software development lifecycle

  • CI focuses on integrating code changes frequently and running automated tests

  • CD focuses on deploying code changes to production environments

  • It helps in reducing manual errors, improving software quality, and increasing development speed

  • Popular ...read more

Q45. Explain the architecture of the project

Ans.

The project follows a microservices architecture with a combination of RESTful APIs and message queues.

  • The project is divided into multiple small services that communicate with each other through APIs and message queues.

  • Each service is responsible for a specific functionality and can be deployed independently.

  • The APIs are designed to be stateless and follow RESTful principles.

  • The message queues are used for asynchronous communication between services.

  • The project uses containe...read more

Q46. Web Api implementation and pattern used

Ans.

Web API implementation using RESTful architecture with MVC pattern.

  • Use RESTful principles for designing API endpoints

  • Implement controllers to handle incoming requests and return responses

  • Leverage MVC pattern for separating concerns and improving maintainability

  • Utilize DTOs (Data Transfer Objects) for transferring data between layers

  • Implement authentication and authorization mechanisms for secure access

Q47. What are oops concept

Ans.

OOPs concepts are the fundamental principles of Object-Oriented Programming.

  • Encapsulation: Binding data and functions that manipulate the data together.

  • Inheritance: Acquiring properties and behavior of a parent class by a child class.

  • Polymorphism: Ability of an object to take many forms.

  • Abstraction: Hiding implementation details and showing only functionality.

Q48. Code review of given java classes

Ans.

Reviewing Java classes for code quality and best practices

  • Check for proper naming conventions and readability of code

  • Ensure that the code follows SOLID principles and design patterns

  • Look for potential bugs, performance issues, and security vulnerabilities

  • Verify that the code is well-documented and includes appropriate comments

  • Evaluate the test coverage and quality of unit tests

Q49. Explain flow about SCM

Ans.

SCM (Software Configuration Management) is the process of managing and controlling changes to software throughout its lifecycle.

  • SCM involves version control, build management, and release management.

  • It ensures that software changes are properly tracked, documented, and controlled.

  • SCM tools like Git, SVN, and Mercurial are used to manage source code and track changes.

  • SCM helps in maintaining code integrity, collaboration among developers, and ensuring reproducibility of softwa...read more

Q50. Design a high performing network queue

Ans.

Design a high performing network queue

  • Use a priority queue to ensure efficient ordering of tasks

  • Implement efficient data structures like linked lists or arrays for storing the queue elements

  • Optimize for fast insertion and removal operations

  • Consider using multithreading or parallel processing for handling multiple requests simultaneously

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