$lock and $LOCK fields will of course not be generated if you already created them yourself. You can also choose to lock on another field, by specifying it as parameter to the @Synchronized annotation. In this usage variant, the fields will not be created automatically, and you must explicitly create them yourself, or an error will be emitted.
Locking on this or your own class object can have unfortunate side-effects, as other code not under your control can lock on these objects as well, which can cause race conditions and other nasty threading-related bugs.
+
+ If you would prefer java.util.concurrent.locks style locks (recommended if you're using virtual threads), have a look at @Locked.