i guess what it means is that code or a method that is synchronized can call other synchronized methods and therefore can have multiple locks on multiple synchronized methods. Hope it helps a little
A single thread can obtain multiple locks on multiple objects As long as an object lock has not been taken by some thread it is available for grab by any thread. So it is perfectly ok for one thread to hold many locks. (or on the same object) This is what we call re-entrance, see this discussion: https://coderanch.com/t/237370/java-programmer-SCJP/certification/sleep-thread-locks