IoC is a principle where the Spring Container manages object creation and lifecycle, not the application code itself.

By default, Spring creates beans as singletons - one instance per application context, shared across the entire application.

Constructor-based DI ensures mandatory dependencies are provided at object creation time and is considered a best practice for required dependencies.

The <bean> element is the standard XML element used in applicationContext.xml to define Spring beans.

@Autowired performs type-based dependency injection. Spring looks for a bean of the required type and injects it automatically.

Valid scopes are singleton, prototype, request, session, application, and websocket. 'eternal' is not a valid scope.

DI reduces coupling by injecting dependencies rather than creating them internally, making code more testable and maintainable.

@Component is a generic stereotype annotation for any Spring-managed component. @Bean is used on methods, while @Service and @Controller are specialized versions of @Component.

map() is an intermediate operation that returns an IntStream. The lambda expression (x -> x * 2) transforms each int, but map() itself returns IntStream, not the transformed value type.

removeIf() removes all elements that satisfy the lambda predicate. Strings with length > 5 are "banana" (6 chars) and "cherry" (6 chars). Only "apple" (5 chars) remains as its length is not greater than 5.