What does intrinsic lock actually mean for a Java class?

Question

In order to properly understand the issues and solutions for concurrency in Java, I was going through the official Java tutorial. In one of the pages they defined Intrin

Answer 1

It doesn't matter whether the synchronized method belongs to the same class or not, what matters is if the caller thread of the method acquires the lock or not, if it does, then it will be allowed enter the critical section because the lock is reentrant.

If it wasn't the case, then a recursive call would cause a deadlock,

fn(){
 synchronized(mutex){ // the current thread has already acquired the mutex
   fn();
 }
}

fn here wont deadlock because the lock is re-entrant, ie ( the thread that's already acquiring the lock can enter and renter the critical section again as long as it is still acquired).