can dragger Interview Questions and Answers

1. What is Dagger?

   • Answer: Dagger is a fast, efficient, and feature-rich dependency injection framework for Android and Java. It generates code at compile time to eliminate the runtime overhead associated with reflection-based dependency injection.

2. What are the benefits of using Dagger?

   • Answer: Benefits include compile-time dependency verification (catching errors early), improved code readability and maintainability, reduced boilerplate code, and better testability through dependency injection.

3. Explain the difference between Dagger 1 and Dagger 2.

   • Answer: Dagger 2 is a complete rewrite of Dagger 1, using the Java annotation processing API for code generation. This results in significantly improved performance and reduced boilerplate compared to Dagger 1's reflection-based approach.

4. What is dependency injection?

   • Answer: Dependency injection is a design pattern where dependencies are provided to a class instead of the class creating them itself. This improves modularity, testability, and maintainability.

5. What is a component in Dagger?

   • Answer: A component is an interface that Dagger generates an implementation for. It defines which dependencies are provided and which classes (or modules) provide them.

6. What is a module in Dagger?

   • Answer: A module is a class annotated with `@Module` that provides dependencies. It contains methods annotated with `@Provides` that Dagger uses to create dependencies.

7. What is the purpose of `@Inject` annotation?

   • Answer: `@Inject` is used to mark constructor parameters or fields that should be provided by Dagger. Dagger uses this annotation to know which dependencies to inject.

8. Explain the difference between `@Provides` and `@Binds`.

   • Answer: `@Provides` creates an instance of a dependency, while `@Binds` binds an interface to an implementation. `@Binds` requires an abstract method in an interface and cannot be used to create new instances.

9. What is a `@Component.Builder`?

   • Answer: `@Component.Builder` is an interface generated by Dagger that allows you to provide dependencies to the component in a configurable way.

10. How do you handle dependencies that have dependencies themselves?

    • Answer: Dagger handles this recursively. If a dependency requires other dependencies, Dagger will automatically resolve and provide them during dependency injection.

11. Explain the concept of Scopes in Dagger.

    • Answer: Scopes like `@Singleton` or custom scopes ensure that dependencies are created only once and reused throughout the application's lifecycle, or a specific scope.

12. How do you create a custom scope in Dagger?

    • Answer: You create a custom scope by creating a custom annotation (e.g., `@ActivityScope`) and marking both the component and the provided dependency with that annotation.

13. What is the role of `@Qualifier` annotation?

    • Answer: `@Qualifier` is used when you have multiple implementations of the same interface and need to specify which one to inject. It distinguishes between similar dependencies.

14. How do you handle subcomponents in Dagger?

    • Answer: Subcomponents are used to create a hierarchical structure, enabling better organization and lifecycle management of dependencies. A parent component can create subcomponents with their own dependencies and scopes.

15. What is the purpose of `@Subcomponent`?

    • Answer: `@Subcomponent` annotation is used to declare subcomponents within a component, allowing for better organization and scoping of dependencies.

16. How do you inject dependencies into activities and fragments?

    • Answer: You typically inject dependencies into activities and fragments through their constructors, using the `@Inject` annotation.

17. How does Dagger handle Android lifecycles?

    • Answer: Dagger works well with Android lifecycles through the use of scopes, ensuring dependencies are created and destroyed appropriately when components are created and destroyed (e.g., Activity or Fragment scopes).

18. What are some common pitfalls when using Dagger?

    • Answer: Common pitfalls include improper scoping, circular dependencies, and forgetting to include necessary modules or components.

19. How to debug Dagger related issues?

    • Answer: Debugging Dagger issues often involves examining the generated code, checking for circular dependencies, ensuring proper scoping, and verifying that modules are correctly included in components.

20. What is Hilt?

    • Answer: Hilt is a dependency injection library that simplifies Dagger usage in Android by providing a standardized way to set up dependency injection in your Android applications.

21. What are the advantages of using Hilt over Dagger directly?

    • Answer: Hilt reduces the boilerplate code required to set up Dagger in an Android project, providing a more streamlined and convenient way to handle dependencies.

22. How does Hilt integrate with Android components (Activities, Fragments, etc.)?

    • Answer: Hilt provides pre-defined components and annotations to easily integrate with Android components. You use annotations like `@AndroidEntryPoint` to inject dependencies automatically.

23. Explain the concept of `@EntryPoint` in Hilt.

    • Answer: `@EntryPoint` allows you to access dependencies from a specific component outside of the standard injection points provided by Hilt. This is useful when dealing with libraries or components not directly managed by Hilt.

24. What is the difference between `@InstallIn` and `@BindsInstance` in Hilt?

    • Answer: `@InstallIn` specifies the component where a module should be installed, while `@BindsInstance` allows you to pass parameters to a component's constructor.

25. How does Hilt handle scoping?

    • Answer: Hilt leverages Dagger's scoping mechanisms, but with pre-defined scopes and a simplified approach for common Android components.

26. Can you use Dagger and Hilt together in the same project?

    • Answer: Generally, it's not recommended to mix Dagger and Hilt directly in the same project as it can lead to conflicts and confusion. Hilt is designed as a replacement for much of the manual Dagger setup.

27. How to migrate from Dagger to Hilt?

    • Answer: Migration involves gradually replacing your Dagger setup with Hilt's annotations and components, focusing on common Android components first.

28. Question 21: Explain the significance of the `@Module` annotation in Dagger?

    • Answer: The `@Module` annotation marks a class that provides dependencies. It indicates to Dagger that this class contains methods to create or fetch dependencies to be injected into other classes.

29. Question 22: What is the role of `@Component` in Dagger 2?

    • Answer: The `@Component` annotation defines an interface that serves as a blueprint for Dagger to generate the dependency injection graph. It specifies which modules are included and what dependencies it can provide.

30. Question 23: Describe the purpose of the `@Provides` annotation.

    • Answer: `@Provides` is used to annotate methods within a module that are responsible for creating or providing dependencies. It tells Dagger how to create instances of the dependencies.

31. Question 24: What's the difference between field injection and constructor injection in Dagger?

    • Answer: Constructor injection involves injecting dependencies through a class's constructor, ensuring that the object cannot be instantiated without its dependencies. Field injection injects dependencies directly into fields annotated with `@Inject`, but offers less control and can be harder to test.

32. Question 25: Explain how Dagger handles dependency cycles.

    • Answer: Dagger cannot handle circular dependencies. If class A depends on class B and class B depends on class A, it will result in a compilation error. Proper dependency design is crucial to avoid this.

33. Question 26: What is the significance of the `@Singleton` scope?

    • Answer: `@Singleton` ensures that a dependency is instantiated only once during the application's lifetime. This is often used for dependencies that don't require a specific lifecycle.

34. Question 27: How do you inject dependencies into a ViewModel in Android using Dagger?

    • Answer: You'd typically use a module that provides the ViewModel and inject dependencies into its constructor. Then, use a `ViewModelProvider.Factory` to create the ViewModel in your Activity or Fragment, providing the dependencies through the factory.

35. Question 28: Explain the use of `@Named` annotation in Dagger.

    • Answer: `@Named` allows you to provide different names to dependencies that share the same type, resolving ambiguity when injecting dependencies.

36. Question 29: What are some best practices for using Dagger?

    • Answer: Best practices include: proper scoping, avoiding circular dependencies, using clear naming conventions, keeping modules small and focused, and using a consistent injection style (mostly constructor injection).

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