Java: Controllers, Services, Repositories

Constructor injection ensures immutability and easier testing.

Constructor injection requires dependencies to be provided at object creation, promoting immutability and making the code easier to test. A class that uses constructor injection is guaranteed to have all its dependencies set, reducing the risk of NullPointerExceptions. In a Spring Boot application, you might have a @Service class for processing orders that receives a @Repository dependency through its constructor, ensuring that the service is fully initialized at runtime.