Synchronized Vs Semaphore

Question

While reading concurrency in Java, I have following doubts:

1. Does Java provides lower level construct then synchronized for synchronization?

2. In

Answer 1

1. There is also volatile keyword, according to http://docs.oracle.com/javase/tutorial/essential/concurrency/atomic.html volatile variable access is more efficient than accessing these variables through synchronized code

2. java.util.concurrent.Semaphore is used to restrict the number of threads that can access a resource. That is, while synchronized allows only one thread to aquire lock and execute the synchonized block / method, Semaphore gives permission up to n threads to go and blocks the others.