Dependency Injection and Design Patterns in .NET Quiz Quiz

Explore your fundamental understanding of dependency injection and common design patterns in .NET with this engaging quiz. Strengthen your grasp of key principles, terminology, and practical scenarios to enhance your software design skills.

1. Basic Concept of Dependency Injection

   Which statement best describes dependency injection in the context of object-oriented programming?

   1. It provides objects their dependencies from external sources rather than creating them internally.
   2. It refers to copying functionality from another class directly.
   3. It allows objects to inherit private fields from another object.
   4. It is the process of renaming variables to avoid conflicts.

   Explanation: Dependency injection means dependencies are given to a class from the outside, promoting loose coupling. Copying functionality is not injection but duplication. Renaming variables and inheriting private fields are unrelated to the concept. Only the correct answer defines dependency injection accurately.

2. Purpose of the Singleton Pattern

   What is the main purpose of using the Singleton design pattern in a .NET application?

   1. To replace the need for constructors in classes.
   2. To manage unrelated classes with a common interface.
   3. To ensure a class has only one instance throughout the application's lifetime.
   4. To allow multiple objects to communicate without direct references.

   Explanation: The Singleton pattern ensures only one instance of a class exists, controlling global access. Allowing objects to communicate without direct references relates to observer or mediator patterns. Managing unrelated classes is the adapter or facade pattern's purpose. Constructors are still used with Singleton; they are not replaced.

3. Transient Service Lifetime

   In .NET dependency injection, which option correctly describes a transient service lifetime?

   1. A new instance is created every time the service is requested.
   2. The service is instantiated during application startup.
   3. A single instance is shared throughout the application.
   4. The instance is created only once per HTTP request.

   Explanation: Transient lifetime means a new instance is created upon each request, ensuring unique objects. A single shared instance describes a singleton. Once per HTTP request characterizes scoped services, and instantiation at startup does not define transient lifetime.

4. Advantages of Constructor Injection

   Why is constructor injection commonly preferred for dependency injection in .NET?

   1. It complicates code readability by hiding dependencies.
   2. It makes dependencies explicit and supports better testing.
   3. It leads to tighter coupling between classes.
   4. It prevents the use of interfaces in class design.

   Explanation: Constructor injection lists required dependencies in the constructor, making them explicit and simplifying unit testing. Hiding dependencies complicates readability, not improves it. The use of interfaces is enhanced by constructor injection, and it actually reduces, not increases, tight coupling.

5. Factory Pattern Application

   Which scenario best matches when to use the Factory design pattern?

   1. When you need to instantiate objects of multiple related types without specifying their concrete classes.
   2. When you want a single class to have only one instance.
   3. When you want to add functionality to objects dynamically.
   4. When you want to restrict access to parts of an object.

   Explanation: The Factory pattern creates objects without revealing the concrete classes to the client, perfect for multiple types. Creating a single instance is a Singleton; adding functionality dynamically is the decorator pattern, and restricting access is more related to the proxy pattern.

6. Interface Usage in DI

   Why are interfaces important when implementing dependency injection in .NET components?

   1. They are always required for inheritance.
   2. They allow you to switch implementations without changing dependent code.
   3. They force implementation of private methods in classes.
   4. They prevent the use of multiple constructors.

   Explanation: Interfaces enable swapping different implementations easily, improving flexibility. Interfaces do not deal with private methods or restrict constructor usage. While useful for inheritance, that is not their main role in dependency injection.

7. Decorator Pattern Function

   What is the main role of the Decorator design pattern in application development?

   1. It creates a single shared instance of a class.
   2. It hides the real implementation of an interface.
   3. It adds new functionality to objects dynamically without changing their structure.
   4. It manages database connections automatically.

   Explanation: The Decorator pattern allows adding functionality to objects at runtime. Singleton relates to shared instances, not decoration. Database connections or hiding implementations are unrelated to the decorator's purpose.

8. Dependency Inversion Principle

   In relation to dependency injection, what does the Dependency Inversion Principle suggest?

   1. Global variables should be used for sharing data between modules.
   2. Methods should have as few parameters as possible.
   3. Classes should only depend on concrete implementations.
   4. High-level modules should not depend on low-level modules; both should depend on abstractions.

   Explanation: The principle promotes reliance on abstractions, enhancing flexibility and testability. Depending only on concrete classes limits reusability. Minimizing method parameters and using global variables are unrelated to dependency inversion.

9. Scoped Service Lifetime

   What happens when a service is registered as 'scoped' in .NET dependency injection?

   1. The service cannot be resolved by the container.
   2. A new instance is created per web request or logical operation.
   3. A single instance lasts for the entire application.
   4. A new instance is created every time the service is needed.

   Explanation: Scoped services get a unique instance per web request, ideal for context-based data. Single instances represent singleton, whereas transient gets new instances every use. Services can always be resolved if properly registered, so the last distractor is incorrect.

10. Facade Pattern Purpose

    What is the main purpose of the Facade design pattern in software design?

    1. To inherit functionality from multiple classes simultaneously.
    2. To provide a simplified interface to a set of complex subsystems.
    3. To control object creation across multiple threads.
    4. To enable direct memory access for speed improvements.

    Explanation: The Facade pattern gives a single, easy-to-use interface for complex systems. It does not enable multiple inheritance, direct memory access, or directly manage thread-based object creation. Its strength lies in reducing complexity for clients.

11. Service Registration in DI

    Which term best describes the process of informing the dependency injection system about which implementation to provide for an interface?

    1. Inheritance mapping
    2. Method overriding
    3. Object serialization
    4. Service registration

    Explanation: Service registration links interfaces to implementations within the DI system. Method overriding changes behavior in derived classes, inheritance mapping is unrelated, and serialization refers to converting objects to data formats, not DI.

12. Liskov Substitution Principle

    Why is the Liskov Substitution Principle important in the context of design patterns and dependency injection?

    1. It requires the use of abstract classes over interfaces.
    2. It enforces single responsibility in every class.
    3. It limits the number of dependencies injected into a class.
    4. It ensures derived classes can replace base classes without breaking the application's correctness.

    Explanation: The Liskov Substitution Principle maintains that derived classes should substitute base classes seamlessly. Single responsibility is a separate principle, not directly related. Choosing abstract classes over interfaces and limiting dependencies are not part of this principle.

13. Constructor Overload and DI

    What risk arises when a class intended for dependency injection contains overloaded constructors?

    1. Interfaces become inaccessible due to constructor overloads.
    2. The system may not know which constructor to use, resulting in errors during resolution.
    3. The class cannot be instantiated at all.
    4. Dependencies will be injected twice, causing duplicate initialization.

    Explanation: Having multiple constructors can confuse the DI system about which to call, creating resolution errors. Injecting dependencies usually happens once, not twice. It doesn't prevent instantiation, but might fail if no clear constructor exists. Constructor overloads don't affect interface accessibility.

14. Open/Closed Principle

    According to the open/closed principle, how should classes be designed?

    1. They can never implement more than one interface.
    2. They should allow direct modification of all member variables.
    3. They should be open for extension but closed for modification.
    4. They must only contain abstract methods.

    Explanation: This principle promotes extending class behavior without altering existing code, aiding maintainability. Direct modification of variables is discouraged. There is no requirement that classes only hold abstract methods, and multiple interface implementations are allowed.

15. Advantages of Using Interfaces

    Which benefit is most directly gained by using interfaces in dependency injection?

    1. Forcing all methods to be static.
    2. Mandating variable initialization in constructors.
    3. Increasing the size of the compiled application.
    4. Enabling easy unit testing and replacement of dependencies.

    Explanation: Interfaces make it simple to swap out real dependencies for test versions, facilitating unit testing. They have no bearing on method staticness, mandatory variable initialization, or application size.

16. Builder Pattern Goal

    What is the main goal of the Builder design pattern when constructing objects?

    1. To guarantee that only one object of a class exists.
    2. To check user permissions in real time.
    3. To construct complex objects step by step with clear separation of construction and representation.
    4. To ensure services are always processed synchronously.

    Explanation: The Builder pattern constructs complex objects incrementally, aiding clarity. Guaranteeing a single object is Singleton's aim. Permission checking and ensuring synchronous processing have nothing to do with Builder's core objective.