Why is it important to inject dependencies into a class or module?

Dependency Injection is important because it increases the modularity and testability of the code. Instead of the class creating or searching for its dependencies itself, they are passed to it from outside. This allows:

• Easily replacing dependencies with mocks or stubs during testing.
• Reducing coupling between components.
• Improving code readability and maintainability.

For example, in Android, instead of creating a repository object inside an Activity, it can be passed through the constructor or using a DI framework (Dagger, Hilt). This makes it easier to replace the repository with a test version.