Viewics Senior Java Developer Interview Questions and Answers

Program using Java 8 features to filter a list of strings starting with 'A' and convert them to uppercase.

• Use Java 8 stream API to filter the strings starting with 'A'.

• Use map() function to convert the filtered strings to uppercase.

• Collect the results into a new list using collect() function.

To connect two databases in Spring Boot, you can configure multiple data sources and use JPA to interact with them.

• Configure multiple data sources in application.properties or application.yml file

• Define multiple DataSource beans in your configuration class

• Use @Primary annotation to specify the primary data source

• Use @Qualifier annotation to specify which data source to use in a specific repository or service

• Use @Transa...read more

An index in MySQL is a data structure that improves the speed of data retrieval operations on a database table.

• Indexes are used to quickly locate rows in a table without having to search every row.

• They can be created on one or more columns in a table.

• Indexes can be unique, which means that the indexed columns must contain unique values.

• Examples of indexes include primary keys, unique keys, and regular indexes.

Post mapping is used to create or update data, while get mapping is used to retrieve data. Yes, data can be updated using post mapping.

• Post mapping is used to create or update data in the server, while get mapping is used to retrieve data from the server.

• Post mapping is typically used for operations that modify data, such as creating a new resource or updating an existing one.

• Get mapping is used for operations that do ...read more

Design patterns in microservices architecture help in solving common problems and improving scalability, maintainability, and flexibility.

• Service Registry pattern - used for service discovery and registration, such as Netflix Eureka

• Circuit Breaker pattern - prevents cascading failures by failing fast and providing fallback mechanisms, like Hystrix

• API Gateway pattern - acts as a single entry point for clients to access ...read more

SOLID principles are a set of five design principles in object-oriented programming to 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: Classes should be open for extension but closed for modification.

• L - Liskov Substitution Principle: Objects of a superclass should be replaceable with obje...read more

Spring Boot simplifies the development of Spring applications by providing out-of-the-box configurations and reducing boilerplate code.

• Spring Boot provides a quick and easy way to set up a Spring application with minimal configuration.

• It includes embedded servers like Tomcat, Jetty, or Undertow, eliminating the need for deploying WAR files.

• Auto-configuration feature in Spring Boot automatically configures the applicati...read more

ExecutorService is an interface in Java that provides a way to manage and control the execution of threads in a multithreaded environment.

• It is part of the java.util.concurrent package.

• It provides methods to submit tasks for execution, manage thread pools, and control the execution of tasks.

• It allows for the execution of tasks asynchronously and provides features like scheduling, cancellation, and monitoring of tasks.

• E...read more

JPA is a Java specification for mapping Java objects to relational databases.

• JPA stands for Java Persistence API

• It provides a way to map Java objects to database tables and vice versa

• JPA simplifies the development of data access layer in Java applications

• It supports object-relational mapping (ORM) and allows developers to work with entities, relationships, and queries in a more object-oriented way

PreparedStatement is used in Java to execute parameterized SQL queries to prevent SQL injection attacks.

• PreparedStatement is a subinterface of Statement in Java.

• It is used to execute parameterized SQL queries.

• It helps prevent SQL injection attacks by automatically escaping special characters.

• Example: PreparedStatement pstmt = connection.prepareStatement("SELECT * FROM users WHERE username = ?");

Program to find missing numbers from Array

• Iterate through the array and store each number in a HashSet

• Then iterate from 1 to the length of the array and check if each number exists in the HashSet

• If a number is not found in the HashSet, it is a missing number

Garbage collection in Java is the process of automatically reclaiming memory by destroying unused objects.

• Garbage collection is performed by the JVM to free up memory occupied by objects that are no longer needed.

• It involves identifying and deleting objects that are no longer reachable by any part of the program.

• Java provides automatic garbage collection, so developers do not have to manually manage memory allocation a...read more

The first statement creates a string literal in the string pool, while the second statement creates a new string object in the heap memory.

• String s = "xyz" creates a string literal in the string pool.

• String s = new String("xyz") creates a new string object in the heap memory.

• Using String s = new String("xyz") can lead to unnecessary memory usage.

JVM is the virtual machine that runs Java programs, JRE is the runtime environment for Java programs, and JDK is the development kit for creating Java programs.

• JVM (Java Virtual Machine) is the virtual machine that runs Java bytecode and converts it into machine code.

• JRE (Java Runtime Environment) is the environment in which Java programs are executed. It includes JVM, libraries, and other necessary components.

• JDK (Jav...read more

The public static void main method is the entry point of a Java program, where execution begins.

• It must be declared as public so that it can be accessed from outside the class.

• It must be declared as static so that it can be called without creating an instance of the class.

• It must have a return type of void, indicating that it does not return any value.

• It takes an array of strings (String[] args) as a parameter, which a...read more

final is a keyword used to declare constants, finally is a block used in exception handling, and finalize is a method used for cleanup.

• final keyword is used to declare constants that cannot be changed

• finally block is used in exception handling to ensure a piece of code is always executed

• finalize method is used for cleanup operations before an object is garbage collected

HashSet is a collection class in Java that stores unique elements using a hash table.

• Uses hashing to store elements

• Does not maintain insertion order

• Allows null values

• Implements Set interface

ArrayList is a resizable array implementation in Java.

• ArrayList is a class in Java that implements the List interface.

• It allows dynamic resizing of the array, unlike regular arrays.

• Elements can be added, removed, or accessed using index.

• Example: ArrayList names = new ArrayList<>();