20 common questions with answers that might be asked during an interview for a Junior Java Developer position

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This list of questions isn’t really a study guide for interviews. We think of it more as a way for you to test yourself to see if you’re ready for the interview.
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What is Java?
- Java is a high-level, class-based, object-oriented programming language that is designed to have as few implementation dependencies as possible. It is used for developing application software and deploying it in a cross-platform computing environment.
What are the key features of Java?
- Some key features include object-oriented, platform independent, robust, secure, high performance, multithreaded, and portable.
What is Spring Boot and why is it used?
- Spring Boot is a project built on the top of the Spring Framework. It provides a simpler and faster way to set up, configure, and run both simple and web-based applications. It is used for its ability to auto-configure itself, depending on the applications you add to the project.
Can you explain the Java memory model?
- The Java memory model specifies how the Java virtual machine works with the computer’s memory (RAM). It includes areas such as the heap, stack, code, and static area, which are used during the execution of a program.
What is the difference between JDK, JRE, and JVM?
- JVM (Java Virtual Machine): Executes Java bytecode and provides an environment for executing Java applications.
- JRE (Java Runtime Environment): Includes JVM and libraries required for running Java applications.
- JDK (Java Development Kit): Includes JRE and development tools needed to develop Java applications.
What is dependency injection in Spring?
- Dependency injection is a design pattern used in Spring where an object receives its dependencies from an external source rather than creating them itself. This helps in wiring objects and managing dependencies cleanly and efficiently.
How does the @Autowired annotation work in Spring?
- The @Autowired annotation allows Spring to resolve and inject collaborating beans into your bean. It can be used on constructor parameters, setters, and properties to automatically wire beans by type.
What is an Interface in Java?
- An interface in Java is a reference type, similar to a class, that can contain only constants, method signatures, default methods, static methods, and nested types. Interfaces cannot contain instance fields. The methods in interfaces are abstract by default.
Explain polymorphism in Java.
- Polymorphism is the ability of an object to take on many forms. It mainly occurs in two ways in Java: method overloading (compile-time polymorphism) and method overriding (runtime polymorphism).
What are exceptions in Java?
- Exceptions are unwanted or unexpected events, which occur during the execution of a program i.e., at runtime, that disrupts the normal flow of the program’s instructions.
What is the Spring framework?
- Spring is a powerful, lightweight framework used for enterprise Java (JEE). It is used for building applications and configurations through inversion of control (IOC), and provides extensive support for integrating other frameworks.
What are Spring Beans?
- Beans are objects that are instantiated, managed, and wired by the Spring IoC container. These beans are created with the configuration metadata that you supply to the container.
What is the @SpringBootApplication annotation used for?
- This annotation is used to mark the main class of a Spring Boot application. It combines @Configuration, @EnableAutoConfiguration, and @ComponentScan annotations with their default attributes.
Explain the REST API in the context of a Spring Boot application.
- A REST API in a Spring Boot application is a way to implement HTTP operations. Classes are annotated with @RestController, and methods in these classes provide endpoints that are accessed through HTTP.
How do you manage transactions in Spring?
- Spring provides an abstraction layer for transaction management that is not tied to JTA. The Spring Framework’s transaction support integrates with the Spring’s various data access abstractions.
What is the difference between @Controller and @RestController in Spring?
- @Controller is used to mark classes as Spring MVC Controller. @RestController is a convenience annotation that combines @Controller and @ResponseBody, which means that it uses @Controller and returns domain objects over HTTP message body.
What is a servlet?
- A servlet is a Java programming language class used to extend the capabilities of servers that host applications accessed by means of a request-response programming model.
What is the purpose of the @RequestMapping annotation?
- This annotation is used for mapping web requests onto specific handler functions. It has attributes to customize the request URL, the HTTP method, request parameters, headers, and media types.
How can you secure a Spring Boot application?
- Security in a Spring Boot application can be managed via Spring Security, which provides authentication, authorization, and protection against common attacks.
What are design patterns and can you name a few used commonly in Java?
- Design patterns are well-proven solutions for solving specific problems in software design. Some common patterns include Singleton, Factory, Strategy, and Observer.

Here are 20 additional interview questions and answers tailored for a Junior Java Developer position, with a focus on Java and Spring Boot. These complement the previous set, offering a broader range of topics.

What is a Java ClassLoader?
- A ClassLoader in Java is a part of the Java Runtime Environment that dynamically loads Java classes into the JVM. It is mainly responsible for loading class files from file systems, network locations, or other sources.
What are Java Streams?
- Java Streams are a part of the Java API which allows functional-style operations on streams of elements. They provide a very efficient way to handle large data sets in a declarative way.
What is the Spring Bean lifecycle?
- The Spring Bean lifecycle consists of bean instantiation, population of properties, setting the Bean Name, Bean Factory, Pre and Post Initialization, and finally Destruction.
What is AOP in Spring?
- Aspect-Oriented Programming (AOP) complements Object-Oriented Programming (OOP) by providing another way of thinking about program structure. It is used to increase modularity by allowing the separation of cross-cutting concerns (like logging and security).
How does Spring handle AOP?
- Spring AOP handles cross-cutting concerns by supporting both schema-based and @AspectJ based aspects. It integrates AOP with Spring configuration management.
What is an Enum in Java?
- An enum in Java is a type used to define collections of constants. More powerful than simple enums, Java enums are class-based and support methods, fields, and constructors.
Explain the difference between @GetMapping and @PostMapping annotations in Spring MVC.
- @GetMapping is used to handle the HTTP GET requests matched with given URI expression, while @PostMapping is used to handle the HTTP POST requests matched with given URI expression.
What is the significance of the application.properties file in a Spring Boot application?
- The application.properties file is used in Spring Boot to configure parameters such as database URLs, server configurations, custom configurations, and much more.
How do you handle exceptions in Spring Boot?
- In Spring Boot, exceptions are handled via the @ControllerAdvice annotation that allows you to handle exceptions across the whole application, not just to an individual controller. You can also use the @ExceptionHandler annotation to handle specific exceptions.
What is JPA and Hibernate in the context of Spring?
- JPA (Java Persistence API) is a specification for accessing, persisting, and managing data between Java objects and a relational database. Hibernate is an ORM (Object Relational Mapping) tool that implements the JPA specifications.
What is the use of the @Transactional annotation?
- The @Transactional annotation in Spring is used to declare that a method should be executed within a transactional context, i.e., the changes should either completely succeed or completely fail.
What are microservices in Spring Boot?
- Microservices in Spring Boot refer to the architectural style of developing a single application as a suite of small services, each running in its own process and communicating with lightweight mechanisms, often an HTTP resource API.
What is the purpose of @Query in Spring Data JPA?
- The @Query annotation is used to define a custom query that goes beyond the simple CRUD operations typically handled by Spring Data repositories.
What is the difference between @Component, @Repository, and @Service annotations in Spring?
- @Component is a generic stereotype for any Spring-managed component. @Repository is a stereotype for the persistence layer. @Service marks a class as a service provider.
How can you achieve data validation in Spring MVC?
- Data validation in Spring MVC can be achieved using the @Valid annotation along with Spring’s Validator interface.
What is the role of the @PathVariable annotation?
- The @PathVariable annotation in Spring MVC is used to handle template variables in the request URL mapping, and bind them to method variables.
Explain the concept of Spring Profiles.
- Spring Profiles provide a way to segregate parts of your application configuration and make it available only in certain environments.
What is Spring Security and how is it integrated into a Spring Boot application?
- Spring Security is a framework that provides authentication, authorization, and protection against common attacks. In Spring Boot, it can be integrated by adding Spring Security as a dependency and configuring it either via Java config or convention-based setups.
What is the @EnableAutoConfiguration annotation used for?
- This annotation tells Spring Boot to start adding beans based on classpath settings