20 Quarkus Interview Questions for 0-5 Years Experience

1. What is Quarkus, and why is it used?

Quarkus is a Kubernetes-native Java framework optimized for GraalVM and OpenJDK HotSpot. It is designed for fast startup, low memory consumption, and superior developer experience, making it ideal for building cloud-native applications.

2. What are the key features of Quarkus?

• Fast startup and low memory footprint
• Native image compilation support with GraalVM
• Unified imperative and reactive programming models
• Built-in support for Kubernetes and serverless applications
• Developer-friendly features like live coding and hot reload

3. How does Quarkus compare to Spring Boot?

Quarkus is optimized for Kubernetes-native applications, offering faster startup times and lower memory consumption compared to Spring Boot. While Spring Boot is more established, Quarkus provides better support for microservices and serverless deployments.

4. What are the different modes in which Quarkus can run?

• JVM Mode: Runs on OpenJDK/HotSpot with quick development cycles.
• Native Mode: Uses GraalVM to compile Java applications into native executables, optimizing startup time and memory usage.

5. How does Quarkus optimize application startup and memory usage?

Quarkus optimizes startup time and memory footprint by using ahead-of-time (AOT) compilation, GraalVM native image support, and aggressive build-time processing to reduce runtime overhead.

6. What is Dev Mode in Quarkus?

Quarkus Dev Mode enables live coding, allowing developers to see changes instantly without restarting the application. It provides features like hot reload, live reload, and interactive testing.

7. How do you create a new Quarkus project?

You can create a new Quarkus project using the Quarkus CLI:

mvn io.quarkus.platform:quarkus-maven-plugin:create \
    -DprojectGroupId=com.example \
    -DprojectArtifactId=my-quarkus-app \
    -DclassName="com.example.GreetingResource"

8. What are Quarkus extensions?

Quarkus extensions are modular components that enable additional functionalities such as REST, database connectivity, and messaging. They can be added using:

mvn quarkus:add-extension -Dextensions="quarkus-resteasy"

9. How does Quarkus support dependency injection?

Quarkus uses CDI (Contexts and Dependency Injection) for dependency management. It follows the Jakarta EE CDI specification and allows injecting beans using @Inject annotation.

10. How can you configure Quarkus applications?

Quarkus uses application.properties or application.yaml files for configuration. Custom properties can be defined and injected using the @ConfigProperty annotation.

11. What is the role of GraalVM in Quarkus?

GraalVM enables Quarkus applications to be compiled into native images, significantly improving startup time and reducing memory consumption.

12. How do you build a Quarkus native image?

To build a native image, run:

mvn package -Pnative

Or using GraalVM:

quarkus build --native

13. What is reactive programming in Quarkus?

Quarkus supports reactive programming using Mutiny, an event-driven, lightweight reactive library designed for asynchronous programming.

14. How does Quarkus handle RESTful services?

Quarkus supports RESTful services through RESTEasy, an implementation of JAX-RS. Example:

@Path("/hello")
public class GreetingResource {
    @GET
    public String hello() {
        return "Hello, Quarkus!";
    }
}

15. How do you connect Quarkus with databases?

Quarkus supports Hibernate ORM with Panache, JDBC, and reactive database drivers. Example configuration:

quarkus.datasource.db-kind=postgresql
quarkus.datasource.username=user
quarkus.datasource.password=pass
quarkus.datasource.jdbc.url=jdbc:postgresql://localhost:5432/mydb

16. What is Panache in Quarkus?

Panache is a simplified ORM framework built on Hibernate, making database interactions more developer-friendly by reducing boilerplate code.

17. How does Quarkus handle security?

Quarkus provides built-in support for authentication and authorization using OAuth2, JWT, and Keycloak.

18. How does Quarkus integrate with Kafka?

Quarkus integrates with Apache Kafka using SmallRye Reactive Messaging, allowing event-driven communication between microservices.

19. How do you deploy a Quarkus application on Kubernetes?

Quarkus provides built-in Kubernetes support. You can generate Kubernetes manifests using:

mvn package -Dquarkus.kubernetes.deploy=true

20. What are some common use cases for Quarkus?

• Cloud-native microservices
• Serverless computing
• Fast boot applications for edge computing
• Event-driven architecture