Why is Java synchronized not working as expected?

Question

I\'m trying to figure out how synchronized methods work. From my understanding I created two threads T1 and T2 that will call the same method <

Answer 1

Each A instance has its own B instance. The method addNew is an instance method of B. Therefore, the lock acquired implicitly during calls to addNew is the lock on the receiver B instance. Each thread is calling addNew on a different B, and therefore locking on different locks.

If you want all B instances to use a common lock, create a single shared lock, and acquire it in the body of addNew.