Java Interview Questions With Answers

Learn how strings in Java represent a sequence of characters as objects, and how arrays of characters relate to strings, with examples of string declaration and conversion.

Discover the fundamentals of Java strings, including immutability, string creation, and common methods such as length, substring, contains, join, replace, equals, trim, toLowerCase, toUpperCase, split, indexOf, intern, and valueOf.

Learn how to reverse a string in Java by building a class with a main method, using a for loop to iterate from end to start, and printing the result.

Create a Java class, define a string, use a nested for loop with i and j, compare with charAt, and print duplicates like A and T.

Learn to count and print duplicate characters in a string using nested for loops to compare characters, with the example 'Gautham' showing A and T as duplicates (count = 2).

Master finding vowels in a string and counting them in Java, using string-to-array conversion and a for loop with vowel checks, as seen in common interview questions.

Learn to count words in a Java string by converting the string to an array, iterating with a for loop, and counting spaces to compute the word count.

Learn how to convert a string to characters in Java with toCharArray, store them in a char array, and print each character, comparing string and character.

Discover how the Java StringBuffer class provides a mutable, thread-safe alternative to String, with empty and capacity constructors and methods such as append, insert, delete, and reverse.

Explore the StringBuilder class in Java to create a mutable string, compare it with String and StringBuffer, and learn practical usage with constructors and append for efficient string manipulation.

Explore why strings in Java are immutable: once created, their state cannot change, and operations like concat produce new objects. Understand security and thread-safety benefits of string immutability.

Compare string and stringbuffer in Java: string is immutable and uses a constant pool; stringbuffer is mutable and enables faster concatenation on the heap. Learn equals behavior and memory implications.

Explore the differences between string, stringbuffer, and stringbuilder in Java. Strings are immutable; stringbuffer is thread-safe, stringbuilder is not, and stringbuilder is more efficient, introduced in 1.5 after 1.0.

Learn how to create an immutable class in Java by using a final class and final data members, illustrated with an employee example, getter methods, and its interview relevance.

Explore the Java collections framework, a unified architecture in java.util with interfaces, implementations, and algorithms for storing and manipulating objects. Delve into the collection, list, queue, set, and map hierarchies.

Learn how to implement and use ArrayList in Java, including importing java.util, creating a list, adding elements with list.add, and printing numbers.

Explore how to manipulate an array list in Java by adding elements at specific indexes, retrieving values with get, printing, and using clear and remove operations on lists.

Explore how to use the iterator interface to traverse Java collections, including lists and maps, by checking hasNext and retrieving values with next.

Learn how to implement a LinkedList in Java, create a class, import java.util, and add and print values. Understand why linked lists excel at middle insertions.

Learn to use the Java 8 Stream API filter with a lambda predicate to select even numbers from a list and reduce them to a sum.

Learn how to sum numbers in Java 8 streams using Integer.sum and method references, replacing lambdas with a pre-built sum method, and collect results from a list.

Learn how to use method references in Java with the forEach method, replacing lambda expressions and employing the scope resolution operator to call System.out.println.

Learn how to use the stream API in Java to map and reduce values, doubling elements with map and reduce starting from zero, and print results demonstrated with examples.

Learn how exceptions in java interrupt normal program flow and how exception handling preserves it by catching runtime errors like class not found, ioexception, sql exception, and remote exception.

Differentiate checked and unchecked exceptions in Java by explaining their inheritance, runtime vs compile-time handling, and examples like SQL exceptions and runtime exceptions such as null pointer and arithmetic exceptions.

Explore dependency injection in Spring by wiring a user class into the main application via the application context, using component annotations and scans to resolve object creation.

Learn how the @Autowired annotation in Spring Boot enables dependency injection by wiring beans without manual instantiation, using @Component and component scanning to resolve collaborators.

Build a spring boot mvc app by creating a spring starter project, adding an index.jsp view, and wiring a controller; include tomcat jasper in pom.xml and run on port 8080.

Explore post mapping and get mapping annotations in Spring Boot, including sending data via post requests, form inputs, and running the application to see printed results.

Use get mapping annotations to fetch data from a server side, create a controller method, build a user model list, and render the show user jsp with expression language.

Build a REST API in Spring Boot by creating a user controller, wiring a repository, and returning a list of users with findAll, tested via Postman at /user.

Learn to create a Spring Boot controller, configure the Spring Boot Starter Web dependency in pom.xml, and map /home to return hello world via a REST controller.

Explore microservices architecture with Spring Boot and REST APIs. Learn how independent, loosely coupled services such as account, inventory, and shipping use separate databases to enable rapid, scalable delivery.

Understand how artificial intelligence enables computer systems to perform tasks that typically require human intelligence, analyzing vast data, learning patterns, and making automated decisions that drive productivity and innovation.

Discover how generative AI learns from data to create art, music, and stories, using prompts and models like generative adversarial networks and variational autoencoders, with responsible use.

Learn prompt engineering to instruct computers with step-by-step commands in Java or Python, enabling apps, calculators, and games, and gain patience, problem solving, and creativity as essential skills.