SAP Roles in Java Backend Developer Interview Questions

Java Backend Developer Interview Questions and Answers

SAP Roles in Java Backend Developer

Core Java Questions

What are the key principles of Object-Oriented Programming (OOP)?

Answer: The four principles of OOP are:

• Encapsulation: Wrapping data (variables) and code (methods) into a single unit, such as a class.
• Inheritance: A mechanism to create a new class using the properties and methods of an existing class.
• Polymorphism: The ability to define multiple methods with the same name but different implementations.
• Abstraction: Hiding the implementation details and exposing only the functionality.

Explain the difference between HashMap and ConcurrentHashMap.

Answer:

• HashMap: Not thread-safe, allows one null key, and multiple null values. Used in single-threaded environments.
• ConcurrentHashMap: Thread-safe and does not allow null keys or null values. It uses bucket-level locking to improve performance in multithreaded applications.

What is the Java Memory Model (JMM)?

Answer: The JMM defines how threads interact with memory in Java, ensuring visibility and atomicity of shared variables. It governs concepts like heap memory, stack memory, and synchronization.

Spring Framework Questions

What is Dependency Injection (DI) in Spring?

Answer: Dependency Injection is a design pattern where the Spring container injects the required dependencies into a class. This decouples the object creation process from its usage.

How does the Spring Boot application manage configurations?

Answer: Spring Boot uses application.properties or application.yml for configuration. It supports hierarchical profiles (e.g., application-dev.properties) for environment-specific settings.

Explain REST API and how to create one using Spring Boot.

Answer:

• REST API is a stateless, client-server architecture for web services.
• In Spring Boot, use annotations like @RestController, @RequestMapping, and @GetMapping to define endpoints.

@RestController
@RequestMapping("/api")
public class SampleController {
    @GetMapping("/hello")
    public String hello() {
        return "Hello, World!";
    }
}

                

Cloud and DevOps Questions

SAP Roles in Java Backend Developer

What is Cloud Foundry, and how does it relate to SAP?

Answer: Cloud Foundry is a PaaS (Platform as a Service) solution that allows developers to deploy applications to the cloud with minimal configuration. SAP uses Cloud Foundry for its multi-cloud strategy.

Explain how Docker improves application deployment.

Answer: Docker containerizes applications with all their dependencies, ensuring consistent environments from development to production. It also simplifies scaling and portability.

Practical Questions

Write a Java program to implement a REST API that connects to a database and fetches user details.

@RestController
@RequestMapping("/users")
public class UserController {
    @Autowired
    private UserRepository userRepository;

    @GetMapping("/{id}")
    public ResponseEntity getUserById(@PathVariable Long id) {
        return userRepository.findById(id)
            .map(ResponseEntity::ok)
            .orElse(ResponseEntity.notFound().build());
    }
}

                

How would you debug performance issues in a Java application deployed on Kubernetes?

Answer:

• Use jconsole or JVisualVM to analyze JVM performance.
• Enable logging and use tools like ELK Stack for log aggregation.
• Monitor resource usage with Kubernetes tools like kubectl top and integrate with Prometheus or Grafana.