My suggestion is to use a HashSet instead, it works just like a Vector, and it is faster, one of the newer Collection objects, and cleaner than Vectors. I would avoid Vectors and HashTables as they are from older versions of Java and the Newer Collections classes are newer. I actually had started using Vectors and Hashtables, since I knew them so well, but I changed them to the new Collections, and it actually reduced a bunch of my code.
First, to answer your question about synchronization you might look at the postings under Threads and Synchronization. Second, it looks like the author of the above code is trying to prevent any other threads from accessing the vector until this thread done with his while loop. Though the Vector is synchronized and only be accessed by one thread at a time, in this case if it was not in a sync block another thread could manipulate the vector (add, remove, removeall, etc) any where in the while loop. Third, I would take Mr. Mark Spritzler's advice in the earlier posting and not use Vectors. Good luck, threading/synching can be tricky to understand and debug. Aaron