By entry, they mean when the flow of execution of the program progresses from a statement outside the block to the inside of the block. (Method returns don't count.) Does that answer address your question, or were you asking about the nature of the lock itself?
Joined: May 11, 2001
So for each block of code you can only have one entry?
No- if a method calls itself recursively, for example, a single block of code may be entered more than once, and each time a new lock is obtained on the same monitor. So a given monitor can have multiple locks held on it at the same time - the only catch is, they all have to be held by the same thread.