What are Dependencies? In computer science, a dependency occurs when one component (class, module, etc.) relies on the functionality of another component to operate correctly. For example, a component depends on a component to provide power. Laptop Battery Dependency Injection Dependency Injection (DI) is a powerful technique that helps manage dependencies between components. Instead of a component directly creating the objects it depends on, those dependencies are provided (“injected”) from the outside. This leads to several key benefits. Consider the and scenario. Here's a contrast between traditional instantiation and using Dependency Injection: Laptop Battery Advantages of Dependency Injection: DI makes unit testing a breeze. You can easily replace a real dependency with a mock or stub during testing, allowing you to isolate the component you’re testing and focus on its specific logic. Improved Testability: Your classes don’t have to be tightly bound to specific implementations of their dependencies. This means pieces of your code become more independent, leading to better maintainability. Loose Coupling: You can easily change the underlying implementations of dependencies without breaking the classes that use them. For example, switching from a database logger to a file logger becomes a simple configuration change. Flexibility: Since components are not responsible for creating their dependencies, they become more reusable in different contexts. Reusability: Disadvantages of Dependency Injection: Introducing DI, especially when done manually, can add a layer of complexity to your code with more classes and interfaces to manage. Increased Complexity: Some DI setups can involve writing a decent amount of code for object creation and dependency wiring, though this can be mitigated with DI frameworks. Boilerplate Code: It’s possible to overuse DI, even in cases where it provides minimal benefit. This can lead to unnecessary complexity. Overuse: When to implement Dependency Injection in Your Project? When you prioritize extensive unit testing, DI is a godsend, allowing you to isolate components and test them independently. Testability: If you anticipate needing to swap out implementations (like switching databases, logging mechanisms, or external services), DI provides a seamless way to do so. Flexibility: When you want to minimize the ripple effects of changes, making your code more robust over time, DI fosters loose coupling and promotes long-term health. Long-term maintainability: If you want to write components that are highly reusable in different contexts, DI keeps them free from directly managing their dependencies. Code reusability: Types of Dependency Injection 1. Constructor Injection How it works: The class requires a dependency to be provided when it's constructed. This ensures the always has a functional battery. Laptop Battery Laptop 2. Setter Injection How it works: The can function without a battery initially. Laptop The setter method allows you to inject the dependency later. battery 3. Interface Injection How it works: An external injector would call to provide the battery. inject Additional Considerations & Techniques 1. Ambient Context How it works: A global class acts as storage for dependencies. AmbientContext Before use, the context is initialized (e.g., ). AmbientContext.initialize(batteryInstance) The class retrieves the dependency directly from the when needed. Laptop Battery AmbientContext 2. Service Locator How it works: A class acts as a central registry for dependencies. ServiceLocator Dependencies are registered with the locator (e.g., ). ServiceLocator().register<Battery>(batteryInstance) The class queries the to retrieve the dependency when needed. Laptop ServiceLocator Battery Also published here

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