Answer Posted / kanu butani

The Java programming language provides two basic
synchronization idioms: synchronized methods and
synchronized statements.

The more complex of the two, synchronized statements, are
described in the next section. This section is about
synchronized methods.

To make a method synchronized, simply add the synchronized
keyword to its declaration:

public class SynchronizedCounter {
private int c = 0;

public synchronized void increment() {
c++;
}

public synchronized void decrement() {
c--;
}

public synchronized int value() {
return c;
}
}

If count is an instance of SynchronizedCounter, then making
these methods synchronized has two effects:
First, it is not possible for two invocations of
synchronized methods on the same object to interleave. When
one thread is executing a synchronized method for an
object, all other threads that invoke synchronized methods
for the same object block (suspend execution) until the
first thread is done with the object.
Second, when a synchronized method exits, it automatically
establishes a happens-before relationship with any
subsequent invocation of a synchronized method for the same
object. This guarantees that changes to the state of the
object are visible to all threads.
Note that constructors cannot be synchronized — using the
synchronized keyword with a constructor is a syntax error.
Synchronizing constructors doesn't make sense, because only
the thread that creates an object should have access to it
while it is being constructed.

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