...
Prefer using block synchronization instead of method synchronization when the method contains non-atomic operations that either do not require any synchronization or can use a more fine-grained locking scheme involving multiple private final lock objects. Non-atomic operations can be decoupled from those that require synchronization and executed outside the synchronized block. The guideline CON04-J. Synchronize Use private final lock objects to synchronize classes that may interact with untrusted code using a private final lock object has more details on using private final lock objects and block synchronization.
...