Mutual Exclusion

Java uses an approach based on monitors to express mutual exclusion in a program. A monitor collects together a number of functions (methods in Java's case) which are critical regions, and enforces the constraint the only one of those critical regions be runnable at any one time.

A thread may obtain exclusive access to an object/class via:

Method synchronization
```
synchronized void f() {
    ... 
}
```

Block synchronization

void f() {
   synchronized(this) {
       ...
   }
}

Class locking (locking static methods and fields)
```
synchronized(C.class) {
    ...
}
```

Synchronization method of the Object Class:

wait() - Causes current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object.

public final void wait() throws InterruptedException;
public final void wait(long timeout) throws InterruptedException;
public final void notify();
public final void notifyAll();

notify(), notifyAll() - Wakes up a single/all thread(s) that is waiting on this object's monitor.