Common Java and Spring Boot Interview Questions

Java Interview Questions:

What is Java?

Java is a programming language that was first released by Sun Microsystems in 1995. It is a high-level, class-based, object-oriented programming language designed to be portable, secure, and platform-independent. Java code is compiled into bytecode, which can run on any platform that has a Java Virtual Machine (JVM).

What are the features of Java?

Some of the key features of Java include:

* Object-oriented programming (OOP)

* Platform independence

* Strong memory management and garbage collection

* Security

* Multi-threading and concurrency

* Robust exception handling

* Dynamic linking

* Portable and scalable

What is the difference between JDK, JRE, and JVM?

JDK (Java Development Kit) is a software development kit used for developing Java applications. It includes the Java compiler, runtime environment, and other tools needed for Java development.

JRE (Java Runtime Environment) is the environment in which Java programs run. It includes the JVM and other components needed to run Java applications, but it does not include development tools like the JDK.

JVM (Java Virtual Machine) is an abstract machine that provides a runtime environment in which Java bytecode can be executed. It is responsible for translating the bytecode into machine code that can be executed by the computer.

What is a class in Java?

A class in Java is a blueprint or template for creating objects. It defines the data and behavior of the objects that will be created from it. A class contains fields (variables) and methods (functions) that define the state and behavior of the objects.

What is an object in Java?

An object in Java is an instance of a class. It has its own state (defined by the class's fields) and behavior (defined by the class's methods). Objects can interact with each other by invoking methods and passing messages.

What is inheritance in Java?

Inheritance in Java is a mechanism by which a class can inherit properties (fields and methods) from a parent class. The parent class is called the superclass, and the class that inherits from it is called the subclass. The subclass can override the methods of the superclass or add new methods and fields of its own.

What is polymorphism in Java?

Polymorphism in Java is the ability of an object to take on many forms. It allows a single method or class to have multiple implementations, depending on the context in which it is used. This can be achieved through method overloading or method overriding.

What is encapsulation in Java?

Encapsulation in Java is the process of hiding the internal details of an object and providing a public interface through which other objects can interact with it. This helps to protect the data and behavior of the object from external manipulation and ensures that the object remains in a consistent state.

What is an abstract class in Java?

An abstract class in Java is a class that cannot be instantiated. It is designed to be extended by subclasses that provide concrete implementations of its abstract methods. Abstract classes are used to provide a common interface for a set of related classes.

What is an interface in Java?

An interface in Java is a collection of abstract methods that define a set of behaviors that a class must implement. It is a contract between a class and the outside world that specifies how the class should behave. Interfaces are used to achieve polymorphism and provide a way to separate the definition of behavior from its implementation.

Spring Boot Interview Questions:

What is Spring Boot?

Spring Boot is a popular open-source framework for building web applications in Java. It is designed to simplify the process of setting up and configuring a Spring-based application. Spring Boot provides a range of pre-built configurations and dependencies that make it easy to build production-ready applications quickly.

What are the advantages of using Spring Boot?

Some of the advantages of using Spring Boot include:

• Faster development and deployment of applications

• Automatic configuration of Spring-based applications

• Easy integration with other Spring projects

• Built-in support for popular technologies like JDBC, JPA, and Spring Data

• Simplified dependency management with Maven or Gradle

• Support for testing with JUnit and other testing frameworks

• Production-ready features like health checks and metrics

What is the use of the @SpringBootApplication annotation in Spring Boot?

The @SpringBootApplication annotation is used to indicate that a class is a Spring Boot application. It is a combination of three other annotations: @Configuration, @EnableAutoConfiguration, and @ComponentScan. The @Configuration annotation indicates that the class contains Spring configuration. @EnableAutoConfiguration enables Spring Boot's auto-configuration mechanism. @ComponentScan tells Spring to scan the package and its sub-packages for components to be managed by Spring.

What is the difference between Spring and Spring Boot?

Spring is a popular Java framework for building enterprise applications. It provides a range of modules for building web applications, data access, security, and more. Spring Boot is built on top of the Spring framework and provides a simplified approach to building and deploying Spring-based applications.

What is auto-configuration in Spring Boot?

Auto-configuration is a feature in Spring Boot that automatically configures the application based on the classpath and environment. It eliminates the need for developers to manually configure the application, reducing the amount of boilerplate code needed to get an application up and running.

What is the use of the application.properties (or application.yml) file in Spring Boot?

The application.properties (or application.yml) file is used to configure the Spring Boot application. It contains key-value pairs that define properties like the server port, database connection details, logging settings, and more. The properties can be overridden by environment variables, command-line arguments, or other configuration sources.

What is Spring Data JPA?

Spring Data JPA is a part of the Spring Data project that provides a high-level abstraction over data access frameworks like Hibernate, EclipseLink, and OpenJPA. It provides a simple and consistent programming model for accessing data in a relational database using the Java Persistence API (JPA).

What is Spring Security?

Spring Security is a powerful and highly customizable security framework for Java-based web applications. It provides a range of security features like authentication, authorization, and session management. Spring Security can be easily integrated with Spring-based applications, making it a popular choice for securing web applications.

What is the use of the @RestController annotation in Spring Boot?

The @RestController annotation is used to indicate that a class is a RESTful controller. It combines the functionality of the @Controller and @ResponseBody annotations. The @Controller annotation indicates that the class is a Spring MVC controller, and the @ResponseBody annotation indicates that the return value of the method should be written directly to the response body.

What is the use of the @Autowired annotation in Spring Boot?

The @Autowired annotation is used to inject dependencies into a Spring-managed bean. It enables Spring to automatically wire beans together based on their dependencies, reducing the amount of boilerplate code needed to configure the application. The @Autowired annotation can be used with constructors, fields, and methods.