Synchronized

Every Java object has a lock. A synchronized block uses an object's lock to act like a binary semaphore with the initial value "1", solving the mutual exclusion critical section problem:
Object obj = new Object();
...
synchronized (obj) { // in a method
... // any code, e.g., critical section
}

The construct:
... synchronized method(...) {
... // body of method
}

is an abbreviation for:
... method(...) {
synchronized (this) {
... // body of method
}
}

That is, the entire body of the instance method is a synchronized block on the object (keyword this) the method is in.