Java Developer Interview Questions and Answers

Primitive data types are basic data types provided by the programming language, while non-primitive data types are created by the programmer.

• Primitive data types include int, float, double, char, boolean, etc.

• Non-primitive data types include arrays, classes, interfaces, etc.

• Primitive data types store actual values, while non-primitive data types store references to objects.

Access modifiers control the visibility of classes, methods, and variables. Non-access modifiers provide additional functionality.

• Access modifiers: public, private, protected, default

• Non-access modifiers: static, final, abstract, synchronized

• Example: public class MyClass { private int myVar; }

Java 8 features include lambda expressions, functional interfaces, streams, and more.

• Lambda expressions allow concise syntax for defining anonymous functions.

• Functional interfaces can have only one abstract method and are used for lambda expressions.

• Streams provide a way to process collections of objects in a functional style.

• Optional class helps to avoid NullPointerException by wrapping a value that may be null.

CICD tools automate the process of building, testing, and deploying code changes.

• Popular CICD tools include Jenkins, GitLab CI/CD, CircleCI, and Travis CI

• These tools help in automating the software development lifecycle

• They enable continuous integration, continuous delivery, and continuous deployment

• CICD tools help in improving code quality, reducing manual errors, and increasing development speed

Containerization is a lightweight, portable, and self-sufficient way to package and run applications.

• Containerization involves encapsulating an application and its dependencies into a container image.

• Containers are isolated from each other and share the host OS kernel.

• Popular containerization platforms include Docker and Kubernetes.

• Containerization allows for easy deployment and scaling of applications.

Indexing in SQL is a technique used to improve the performance of queries by creating a data structure that allows for faster retrieval of data.

• Indexes are created on columns in a database table to speed up the retrieval of rows that match a certain condition in a query.

• They work similar to the index in a book, allowing the database to quickly locate the rows that satisfy the query.

• Indexes can be created using a single...read more

A program to check if a given number is prime or not.

• Create a function to check if a number is prime by iterating from 2 to the square root of the number.

• If the number is divisible by any number other than 1 and itself, it is not prime.

• Handle edge cases like 0, 1, and negative numbers separately.

To find the 3rd highest salary employee, we can use a SQL query with the 'LIMIT' and 'OFFSET' keywords.

• Use a SQL query to select distinct salaries in descending order

• Use 'LIMIT 1 OFFSET 2' to get the 3rd highest salary

• Join this result with the employee table to get the employee details

HashMap internally uses an array of linked lists to store key-value pairs.

• HashMap uses hashing to determine the index of the key in the array.

• If multiple keys hash to the same index, a linked list is used to store them.

• When retrieving a value, the key is hashed to find the index and then the linked list is searched for the key.

Vector is synchronized and slower, ArrayList is unsynchronized and faster.

• Vector is synchronized, ArrayList is not.

• Vector is slower due to synchronization, ArrayList is faster.

• Vector is legacy class, ArrayList is part of Java Collections framework.

• Vector doubles its size when full, ArrayList increases by 50%.