Can you explain the concept of dependency injection in Java and how it is applied?

Dependency Injection (DI) is a pattern that allows objects to receive their dependencies from outside rather than creating them internally. In Java, this helps make the code more modular, testable, and maintainable.

Example: instead of a class creating a dependency object inside itself, it receives it through a constructor or setter.

public class Service {
    private Repository repository;

    // Injecting dependency via constructor
    public Service(Repository repository) {
        this.repository = repository;
    }

    public void doWork() {
        repository.save();
    }
}

// When creating a Service object, we pass the required Repository implementation
Repository repo = new DatabaseRepository();
Service service = new Service(repo);

In Java, frameworks like Spring are often used, which automatically manage the creation and injection of dependencies, simplifying development.