synchronized block not locking the object reference

Question

class Demo
{
    void demo()
    {
        System.out.println(\"Inside demo of \"+Thread.currentThread().getName());
        try
        {
            Thread.sleep(10000         


        

Answer 1

Synchronization is a collaborative effort. Each party states that when another party is in a critical section, they won't be.

You've only synchronized access to the demo method of the Demo instance in one thread

synchronized(d)
{
    d.demo();
} 

The other is accessing it directly

d.demo();

They've broken these collaboration rules so you can't assume anything.

This is explained in the JLS

Acquiring the lock associated with an object does not in itself prevent other threads from accessing fields of the object or invoking un-synchronized methods on the object. Other threads can also use synchronized methods or the synchronized statement in a conventional manner to achieve mutual exclusion.