what's the total number of "u"s in:
q: what pattern does slf4j use? the design of slf4j really excited me. i mean the way it introduces the implementing component. in the loggerfactory, it imports org.slf4j.impl.staticloggerbinder, a class in its namespace but that doesn't exist in its jar file. the implementation (like logback) jar just includes the class and it's done. the classloader will do the binding work for you.
this makes the implementing component plugable / drop-in-able, zero configuration, your code only depend on slf4j.
i want to know, does this approach have an orthodox name? or any related design patterns? i want to learn more about it.

a: i believe it is a combination of patterns and well-engineered implementation.
the first pattern that comes to mind is dependency inversion. by defining interfaces, slf4j defers implementation until runtime. another pattern is delegation pattern, which allows the dependency inversion to provide good traction. 
the implementation uses a service loader, as @kapep mentioned, to perform the dependency injection.

user
The total number of "u"s in that passage is thirteen.
assistant