Java™ How To Program (Early Objects), Tenth Edition

23.4.2 Monitors

A common way to perform synchronization is to use Java’s built-in monitors. Every object has a monitor and a monitor lock (or intrinsic lock). The monitor ensures that its object’s monitor lock is held by a maximum of only one thread at any time. Monitors and monitor locks can thus be used to enforce mutual exclusion. If an operation requires the executing thread to hold a lock while the operation is performed, a thread must acquire the lock before proceeding with the operation. Other threads attempting to perform an operation that requires the same lock will be blocked until the first thread releases the lock, at which point the blocked threads may attempt to acquire the lock and proceed with the operation.

To specify that a ...