Java spring boot interview questions and answers
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Java Interview Questions
1. What is the Java Virtual Machine (JVM) and how does it work?
Answer: The JVM is an abstract computing machine that enables a computer to run Java programs (as well as programs written in other languages compiled to Java bytecode). The JVM works by loading code, verifying code, executing code, and providing runtime environments.
2. Explain the concept of Object-Oriented Programming as it applies to Java.
Answer: Object-Oriented Programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data in the form of fields (often known as attributes or properties), and code, in the form of procedures (often known as methods). Java uses OOP principles including inheritance, encapsulation, polymorphism, and abstraction.
3. What are the differences between an abstract class and an interface in Java?
Answer: An abstract class can have both abstract and concrete methods, whereas an interface can only have abstract methods (until Java 8, after which it can have default and static methods). A class can extend only one abstract class but can implement multiple interfaces.
4. How does Java achieve platform independence?
Answer: Java achieves platform independence through its use of the JVM. Java programs are compiled into bytecode, which the JVM then interprets on any platform, allowing the same Java program to run on any device equipped with a JVM.
5. Explain the difference between `==` and `.equals()` in Java.
Answer: In Java, `==` is a reference comparison, i.e., both objects point to the same memory location. The `.equals()` method evaluates to the comparison of values in the objects.
6. What is the purpose of garbage collection in Java, and how does it work?
Answer: Garbage collection in Java is the process of looking at heap memory, identifying which objects are in use and which are not, and deleting the unused objects to reclaim memory. It works by employing algorithms like Mark-and-Sweep or Generational Garbage Collection to efficiently manage memory.
7. Explain the concept of Java collections and the benefits they offer.
Answer: Java Collections Framework provides a set of interfaces and classes for storing and manipulating groups of objects as a single unit. Collections offer benefits like reduced programming effort, increased performance, and the ability to implement algorithms to search, sort, filter, and manipulate data.
8. What is the difference between `final, finally, and finalize` in Java?
Answer: `final` is a keyword used to apply restrictions on class, method, and variable. A final class can't be inherited, a final method can't be overridden, and a final variable’s value can't be changed. `finally` is a block used to place important code, it will be executed whether an exception is handled or not. `finalize` is a method used to perform cleanup processing just before object is garbage collected.
9. How does Java handle exceptions?
Answer: Java handles exceptions through its robust Exception Handling framework which includes try, catch, finally blocks, and throws and throw keywords for throwing an exception. Checked exceptions are checked at compile-time, while unchecked exceptions are checked at runtime.
10. Explain the concept of threading in Java.
Answer: Threading in Java is a concurrency mechanism allowing multiple threads to run in parallel, providing a means for optimizing application performance through asynchronous execution. Threads can be created by extending the Thread class or implementing the Runnable interface.
Spring Boot Interview Questions
11. What is Spring Boot and what are its advantages?
Answer: Spring Boot is an open-source Java-based framework used to create a micro Service. It is developed by Pivotal Team and is used to build stand-alone and production-ready spring applications. Advantages include easy to understand and develop spring applications, embedded server to avoid complexity, and a wide range of plugins for developing applications.
12. Explain auto-configuration in Spring Boot.
Answer: Auto-configuration in Spring Boot is a powerful, flexible mechanism that attempts to automatically configure your Spring application based on the jar dependencies you have added. It simplifies the development process by minimizing the need for manual configuration.
13. What is the purpose of the Spring Boot Starter POMs?
Answer: Spring Boot Starter POMs are a set of convenient dependency descriptors that you can include in your application. Each starter POM provides a comprehensive set of dependencies that are required to build a specific type of application with minimal configuration.
14. How does Spring Boot handle database migrations?
Answer: Spring Boot can handle database migrations using tools like Flyway or Liquibase. These tools allow for version control of your database schema
by applying incremental updates and rollbacks through migration scripts.
15. What is the Spring Boot Actuator and its benefits?
Answer: The Spring Boot Actuator provides built-in endpoints to monitor and manage your application, such as health, metrics, info, dump, env, etc. It's beneficial for application diagnostics and monitoring.
16. How can you customize the Spring Boot embedded server?
Answer: Customization can be achieved by specifying properties in `application.properties` or `application.yml` file, programmatically configuring the embedded server via configuration classes, or by implementing the `WebServerFactoryCustomizer` interface.
17. Explain the role of @SpringBootApplication annotation in Spring Boot.
Answer: The `@SpringBootApplication` annotation is a convenience annotation that adds all of the following: @Configuration, @EnableAutoConfiguration, and @ComponentScan. It's used to enable auto-configuration and component scanning in your application.
18. How does Spring Boot support data access?
Answer: Spring Boot supports data access through Spring Data JPA, Spring Data MongoDB, Spring Data Redis, and other Spring Data projects. It simplifies data access by providing a consistent, Spring-based programming model while also supporting repository and custom object-mapping abstractions.
19. What are Spring Boot Profiles?
Answer: Spring Boot Profiles provide a way to segregate parts of your application configuration and make it available only in certain environments. Profiles can be activated via environment variables, JVM properties, or configuration files.
20. How do you secure a Spring Boot application?
Answer: Spring Boot can be secured using Spring Security, which provides authentication and authorization support. Configuring Spring Security can be done by extending `WebSecurityConfigurerAdapter` and overriding the necessary methods to set up security rules.
21. Explain the concept of Dependency Injection in Spring Boot.
Answer: Dependency Injection (DI) is a design pattern that Spring Boot utilizes to inject objects into a class, instead of the class itself creating the object. This is achieved through the use of `@Autowired` annotation, constructor injection, setter injection, or field injection, promoting loose coupling and easier testing.
22. What is the Actuator in Spring Boot and its use?
Answer: Repeated for emphasis, the Actuator in Spring Boot is a set of management endpoints that allow you to monitor and interact with your application. Spring Boot Actuator provides detailed insights and metrics of application behavior and state through endpoints.
23. How do you externalize configuration in Spring Boot?
Answer: Configuration in Spring Boot can be externalized using properties files, YAML files, environment variables, and command-line arguments. This allows for different configurations in different environments without changing the code.
24. What is the role of the `@RestController` annotation in Spring Boot?
Answer: The `@RestController` annotation is used at the class level in Spring Boot applications to create RESTful web services using Spring MVC. It combines `@Controller` and `@ResponseBody` annotations, ensuring that every method returns a domain object instead of a view.
25. How to implement exception handling in Spring Boot?
Answer: Exception handling in Spring Boot can be implemented using the `@ControllerAdvice` annotation to handle exceptions across the whole application, not just to an individual controller. You can also use the `@ExceptionHandler` annotation to handle specific exceptions.
26. Explain the use of Spring Boot starters.
Answer: Spring Boot starters are a set of dependency descriptors that simplify the Maven or Gradle configuration for your application. They aggregate common dependencies together to reduce boilerplate code and configuration.
27. How to manage transactions in Spring Boot?
Answer: Transactions in Spring Boot can be managed declaratively using the `@Transactional` annotation. This abstraction allows you to apply transactional management to your beans without having to deal with the transaction APIs directly.
28. What is the purpose of the `@EnableAutoConfiguration` annotation in Spring Boot?
Answer: `@EnableAutoConfiguration` tells Spring Boot to start adding beans based on classpath settings, other beans, and various property settings. It's part of the auto-configuration magic that Spring Boot provides.
29. How can Spring Boot be used to build microservices?
Answer: Spring Boot is ideal for building microservices due to its ability to rapidly bootstrap and deploy applications, its embedded server, and its suitability for containerization. It also integrates well with Spring Cloud for microservices patterns like service discovery and configuration management.
30. Describe how Spring Boot integrates with Spring MVC.
Answer: Spring Boot automatically configures Spring MVC with sensible defaults, assuming you're developing a web application. It provides auto-configuration settings to set up MVC with minimal effort, such as dispatcher servlet, view resolvers, and necessary converters and formatters.