Persistent Digital Java Developer Interview: Rounds, Questions and Preparation

What the job involves

Java Developers in Indian IT services build and maintain enterprise applications for clients across domains like banking, insurance, and retail. Day to day, they write Java code, fix bugs, integrate with databases and APIs, and work with senior developers to deliver features on time. Freshers usually start on support or enhancement projects before moving to core development.

Java and OOP Fundamentals

1. 1

   What is the difference between an abstract class and an interface in Java, and when would you use each?

   Explain that abstract classes can have state and constructors, interfaces define contracts, and since Java 8 interfaces can have default methods. Give a real example like a payment system.

2. 2

   How does HashMap work internally in Java?

   Cover hashing, buckets, equals and hashCode contracts, collision handling with linked lists or trees, and load factor. Mention that it is not thread safe.

3. 3

   Explain the difference between checked and unchecked exceptions with examples.

   Checked exceptions must be handled or declared, like IOException. Unchecked exceptions are runtime errors like NullPointerException. Give a short code snippet context.

4. 4

   What are Java 8 streams and how have they changed how you write collection processing code?

   Describe stream as a sequence of elements supporting functional operations like filter, map, and collect. Give an example of filtering a list of employees by salary.

Spring, Database, and Web Basics

1. 5

   What is dependency injection in Spring and why is it useful?

   Explain that Spring manages object creation and wiring, reducing tight coupling. Mention constructor injection and how it helps testing.

2. 6

   How would you design a REST API for a simple employee management system?

   List endpoints like GET /employees, POST /employees, PUT /employees/{id}, DELETE /employees/{id}. Mention HTTP methods, status codes, and JSON request and response.

3. 7

   Write a SQL query to find the second highest salary from an Employee table.

   Show a subquery with MAX or use LIMIT and OFFSET. Explain the logic clearly and mention handling ties.

4. 8

   What is the difference between JDBC and JPA or Hibernate?

   JDBC is low level and requires manual SQL and connection handling. JPA and Hibernate are ORM tools that map objects to tables and reduce boilerplate.

Practical Scenarios and Problem Solving

1. 9

   You are asked to fix a bug in a production Java application that you have never seen before. What steps do you take?

   Talk about reading logs, reproducing the issue, checking recent changes, using a debugger, and writing a unit test before fixing. Mention communication with the team.

2. 10

   Your code works on your machine but fails on the client server. How do you debug this?

   Check environment differences like Java version, database connection strings, file paths, and missing dependencies. Use logs and compare configurations.

3. 11

   How would you optimise a slow SQL query used by a Java application?

   Check indexes, avoid SELECT *, analyse execution plan, reduce joins, and consider pagination. Mention caching if appropriate.

4. 12

   You have to add a new feature to an existing module with no documentation. How do you proceed?

   Read the code, talk to senior developers, write small tests to understand behaviour, and make minimal changes. Mention version control and code review.

Behavioural and HR Questions

1. 13

   Tell me about a time you worked in a team to complete a college project. What was your role?

   Use STAR format. Highlight your specific contribution, how you handled disagreements, and the outcome. Keep it concise.

2. 14

   Are you willing to relocate to any city in India or work in shifts if the project demands it?

   Be honest but positive. Indian IT services often require flexibility. Say yes if you are open, and explain your willingness to learn.

3. 15

   Why do you want to join a services company like Persistent Digital rather than a product company?

   Talk about exposure to multiple domains, client-facing work, structured training, and learning opportunities. Avoid saying it is just a backup.

4. 16

   Where do you see yourself in three years as a Java Developer?

   Show a growth path: from fresher to independent developer, then to module lead or specialist. Mention learning new technologies and contributing to the team.