30+ Interview Questions and Answers

The 4 pillars of OOP are Abstraction, Encapsulation, Inheritance, and Polymorphism.

• Abstraction: Hiding implementation details and showing only necessary information. Example: A car dashboard only shows necessary information like speed, fuel level, etc.

• Encapsulation: Binding data and methods that manipulate the data together. Example: A bank account class with methods to deposit, withdraw, and check balance.

• Inheritance: Creating new classes from existing ones, inheriting their...read more

Java programs are executed by the Java Virtual Machine (JVM) which interprets and executes the bytecode generated by the Java compiler.

• Java source code is compiled into bytecode by the Java compiler

• The bytecode is platform-independent and can be executed on any device with a JVM

• The JVM interprets the bytecode and executes the instructions

• The JVM manages memory, handles exceptions, and provides other runtime services

• Example: javac HelloWorld.java -> java HelloWorld

Java is most secured due to its strong memory management, bytecode verification, and security manager.

• Java's strong memory management prevents buffer overflow and other memory-related vulnerabilities.

• Bytecode verification ensures that the code is safe to execute and prevents malicious code from running.

• Security manager allows fine-grained control over access to system resources.

• Java also has a robust set of security APIs and tools for encryption, authentication, and authoriza...read more

Arrays are fixed in size and can store elements of the same type, while collections are dynamic and can store elements of different types.

• Arrays have a fixed length, while collections can grow or shrink dynamically.

• Arrays can only store elements of the same type, while collections can store elements of different types.

• Arrays use indexed access for retrieval and modification, while collections provide various methods for manipulation.

• Arrays are part of the core Java language, ...read more

Java is a high-level, object-oriented programming language used for developing applications.

• Java features include platform independence, automatic memory management, and exception handling.

• Try and catch blocks are used for handling exceptions in Java.

• Static is a keyword used to create class-level variables and methods.

• ArrayList is a dynamic array that can grow and shrink in size, while HashSet is a collection that does not allow duplicates.

A subquery is a query nested within another query, and the LIKE operator is used in SQL to search for a specified pattern in a column.

• A subquery is enclosed in parentheses and executed first before the main query.

• The result of a subquery can be used in comparison with the main query's result.

• The LIKE operator is used with the WHERE clause to search for a specified pattern in a column.

• The LIKE operator allows for wildcard characters such as % (matches any sequence of character...read more

Count the number of repeated words in a given string

• Split the string into words using a delimiter like space

• Create a hashmap to store word frequencies

• Iterate through the words and update the hashmap accordingly

• Count the number of words with frequency greater than 1

Encapsulation, Inheritance, Polymorphism, Abstraction

• Encapsulation: Bundling data and methods that operate on the data into a single unit

• Inheritance: Ability of a class to inherit properties and behavior from another class

• Polymorphism: Ability to present the same interface for different data types

• Abstraction: Hiding the complex implementation details and showing only the necessary features

String is immutable because its value cannot be changed once it is created.

• String objects are stored in the String pool, which is a part of the heap memory.

• When a string is modified, a new string object is created with the modified value.

• Immutable strings are thread-safe and can be safely shared among multiple threads.

• String immutability allows for efficient memory utilization and optimization.

JDBC involves steps like loading driver, establishing connection, creating statement, executing query and handling results.

• Load the JDBC driver using Class.forName() method

• Establish a connection to the database using DriverManager.getConnection() method

• Create a statement object using the connection.createStatement() method

• Execute the query using statement.executeQuery() method

• Handle the results using ResultSet object

Database connection in Spring Boot is configured using application.properties or application.yml file.

• Define database connection properties in application.properties or application.yml file

• Use @EnableJpaRepositories annotation to enable JPA repositories

• Use @Entity annotation to define entity classes

• Use @Autowired annotation to inject the DataSource or EntityManager

Abstract class is a class that cannot be instantiated and may contain abstract methods.

• Cannot be instantiated directly

• May contain abstract methods that must be implemented by subclasses

• Can have both abstract and non-abstract methods

• Used for creating a template for other classes to inherit from

Strings are immutable to ensure data integrity and security by preventing accidental or intentional modification.

• Immutable strings prevent accidental changes to data

• Enhances security by preventing data tampering

• Allows for efficient memory management

Multi threading is the concurrent execution of multiple threads in a single program.

• Allows multiple tasks to run concurrently

• Improves performance and responsiveness

• Enables efficient utilization of CPU resources

• Can be used for parallel processing

• Examples: running multiple calculations simultaneously, handling multiple client requests

Arrays are fixed in size and store elements of the same data type, while collections are dynamic in size and can store elements of different data types.

• Arrays have a fixed size, while collections can dynamically resize.

• Arrays store elements of the same data type, while collections can store elements of different data types.

• Arrays use indexes to access elements, while collections use iterators or other methods.

• Examples: Array - int[] numbers = {1, 2, 3}; Collection - List name...read more

JDBC steps to connect to a database

• Load the JDBC driver class

• Establish a connection to the database using the DriverManager class

• Create a statement object to execute SQL queries

• Execute the SQL queries and retrieve the results

• Close the statement and connection objects

Controller is a general term for a component that handles user requests, while a REST controller specifically handles RESTful requests.

• Controller is a general term for a component that handles user requests in a web application

• REST controller specifically handles RESTful requests, following the principles of REST architecture

• REST controller typically returns data in JSON or XML format, while a regular controller may return HTML or other formats

Microservices interact with each other through APIs, messaging queues, or event-driven architecture.

• Use RESTful APIs for synchronous communication between microservices

• Implement messaging queues like RabbitMQ or Kafka for asynchronous communication

• Leverage event-driven architecture with tools like Apache Kafka or AWS SNS/SQS

• Consider using service mesh like Istio for managing communication between microservices

Collection is a group of objects while Map is a key-value pair data structure.

• Collection is used to store and manipulate a group of objects.

• Map is used to store and retrieve data based on key-value pairs.

• Collection classes include List, Set, and Queue.

• Map classes include HashMap, TreeMap, and LinkedHashMap.

• Collections allow duplicate elements while Maps do not.

• Example: Collection - List of names, Map - Student ID and corresponding name.

Stream API is a feature in Java that allows processing collections of objects in a functional style.

• Stream API provides a way to perform operations on a collection of objects in a declarative way.

• It supports functional-style operations like map, filter, reduce, and forEach.

• Streams can be created from various sources like collections, arrays, or I/O channels.

• Stream operations are lazy, meaning they are only executed when a terminal operation is called.

• Stream API promotes immut...read more

Multiple DBs can be configured in an application by using database connection pooling, configuring multiple data sources, and managing transactions across databases.

• Use database connection pooling to efficiently manage connections to multiple databases

• Configure multiple data sources in the application to connect to different databases

• Implement transaction management to ensure data consistency across multiple databases

Print highest salary of an employee using coding

• Create an array of employee salaries

• Sort the array in descending order

• Print the first element of the sorted array as the highest salary

Use thread pooling and asynchronous processing to handle multiple requests efficiently in Spring Boot.

• Implement thread pooling to manage multiple requests concurrently.

• Use asynchronous processing to handle requests without blocking the main thread.

• Consider using reactive programming with Spring WebFlux for better scalability.

• Optimize database queries and external API calls to reduce response times.

• Implement caching mechanisms to store and retrieve frequently accessed data.

The life cycle of a thread refers to its various states and transitions during its execution.

• A thread starts in the new state when it is created.

• It moves to the runnable state when it is ready to run but waiting for the CPU.

• When the CPU starts executing the thread, it enters the running state.

• A thread can temporarily move to the blocked or waiting state when it is waiting for a resource or signal.

• A thread can be terminated and move to the dead state when it completes its exec...read more

Production issues are common and require quick resolution to minimize downtime and losses.

• Equipment breakdowns can cause delays and require maintenance or replacement.

• Supply chain disruptions can lead to shortages and delays in production.

• Quality control issues can result in defective products and require process improvements.

• Communication breakdowns between departments can cause delays and errors.

• Regular maintenance and training can prevent issues and improve efficiency.

• Impl...read more

Hibernate connects to the database using JDBC (Java Database Connectivity) API.

• Hibernate uses JDBC API to establish a connection to the database.

• It uses JDBC drivers to communicate with the database.

• Hibernate configuration file contains database connection details.

• SessionFactory in Hibernate is responsible for creating sessions and managing connections.

Spring beans are Java objects managed by the Spring IoC container.

• Spring beans are defined in the Spring configuration file using XML or annotations.

• They are instantiated, assembled, and managed by the Spring IoC container.

• Beans can be singleton, prototype, request, session, or custom scoped.

• Dependency injection is used to inject dependencies into Spring beans.

Spring Boot is a framework that simplifies the development of Java applications by providing pre-configured settings and tools.

• Spring Boot eliminates the need for manual configuration by providing defaults for most settings.

• It allows developers to quickly set up and run standalone Spring-based applications.

• Spring Boot includes embedded servers like Tomcat, Jetty, or Undertow for easy deployment.

• It promotes convention over configuration, reducing the amount of boilerplate code...read more

Spring injects dependencies through inversion of control and dependency injection.

• Spring uses inversion of control to manage objects and their dependencies.

• Dependencies are injected into a class through constructor injection, setter injection, or field injection.

• Spring container is responsible for creating and managing objects and their dependencies.

• Example: @Autowired annotation is used for dependency injection in Spring.

JWT token is a JSON web token used for securely transmitting information between parties as a compact and self-contained way.

• JWT stands for JSON Web Token

• It consists of three parts: header, payload, and signature

• It is commonly used for authentication and information exchange in web development

Oops concept in Java program refers to Object-Oriented Programming principles like inheritance, encapsulation, polymorphism, and abstraction.

• Inheritance allows a class to inherit properties and behavior from another class.

• Encapsulation hides the internal state of an object and only exposes necessary methods to interact with it.

• Polymorphism allows objects of different classes to be treated as objects of a common superclass.

• Abstraction focuses on the essential characteristics o...read more

Securing APIs involves using authentication, authorization, encryption, and monitoring.

• Implement authentication mechanisms such as OAuth, JWT, or API keys

• Use authorization to control access to APIs based on roles and permissions

• Encrypt data transmission using HTTPS/TLS to prevent eavesdropping

• Implement rate limiting and throttling to prevent abuse and DDoS attacks

• Regularly monitor API traffic and logs for suspicious activity

UPI is expected to continue growing in popularity and usage due to its convenience and ease of use.

• UPI transactions are expected to increase as more people adopt digital payment methods.

• Integration of UPI with various platforms and services will further drive its usage.

• Security measures and fraud prevention techniques will continue to evolve to ensure safe transactions.

• Introduction of new features and enhancements will enhance user experience and encourage more people to use ...read more

Various techniques such as Agile, Waterfall, Scrum, Kanban, Lean, etc.

• Agile methodology focuses on iterative development and collaboration

• Waterfall methodology follows a linear sequential flow

• Scrum involves small, cross-functional teams working in sprints

• Kanban visualizes work on a board with columns representing different stages

• Lean aims to eliminate waste and improve efficiency

Software development life cycle refers to the process of planning, creating, testing, and deploying software.

• Requirements gathering and analysis

• Design

• Implementation

• Testing

• Deployment

• Maintenance

• Examples: Waterfall model, Agile methodology

Proficiency in cloud technology is essential for data scientists to efficiently store, manage, and analyze large datasets.

• Experience with cloud platforms like AWS, Azure, or Google Cloud

• Knowledge of cloud storage solutions like S3, Blob Storage, or Cloud Storage

• Understanding of cloud computing concepts like virtual machines, containers, and serverless computing

• Ability to work with big data technologies like Hadoop, Spark, or Kafka in the cloud environment