How does the Spring Framework decide which components to inject at application startup?

The Spring Framework uses Dependency Injection (DI) to automatically inject components when the application starts. The main ways Spring determines which components to inject are:

• Annotations: for example, @Component, @Service, @Repository mark classes as beans that Spring should manage.
• Automatic scanning (component scanning): Spring scans specified packages for such annotated classes and creates their instances.
• Autowiring (@Autowired): Spring searches for a suitable bean by type (and by name if necessary) and injects it into a field, constructor, or setter.

When the container starts, Spring creates a dependency graph, analyzing which beans depend on each other, and automatically links them, providing a ready-to-use application configuration.