Dependency Injection (DI) is a design pattern used in software development to achieve loose coupling between classes or components by externalizing their dependencies. In simpler terms, it's a way of passing objects (dependencies) into a class rather than the class creating those objects itself.
Imagine you have a class called Car that needs an Engine object to function. Without Dependency Injection, the Car class might create an Engine object internally:
public class Car {
private Engine engine;
public Car() {
this.engine = new Engine(); // Creating the Engine object internally
}
}With Dependency Injection, the Car class doesn't create the Engine object itself. Instead, it's provided with the Engine object from the outside:
public class Car {
private Engine engine;
public Car(Engine engine) {
this.engine = engine; // Engine object is passed in from outside
}
}Here, the Car class depends on an Engine object, but it's not responsible for creating it. Instead, the Engine object is "injected" into the Car class from the outside, typically through its constructor.
Dependency Injection promotes modularity, testability, and flexibility in software development:
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Modularity: Classes become more modular and focused on specific tasks when they don't create their own dependencies.
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Testability: It becomes easier to test classes in isolation by providing mock or stub objects during testing, rather than relying on real implementations of dependencies.
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Flexibility: By externalizing dependencies, different implementations of the same interface can be swapped in and out without modifying the classes that depend on them. This allows for easier configuration and adaptation to changing requirements.
In summary, Dependency Injection is a technique for managing dependencies in software development, where dependencies are provided to a class from the outside rather than being created internally. This promotes loose coupling, modularity, testability, and flexibility in the codebase.