What happens if synchronization variable is reassigned in java?

Question

What happens in the following code? Does the synchronization work? This is an interview question.

class T
{
    public static void main(String args[])
    {
        Object myObject = new Object();
        synchronized (myObject)
        {
            myObject = new Object();
        } // end sync
    }
}

Answer 1

Each time you enter the synchronized block, you synchronize on a different object. Most of the time this will not do anything except confuse you, but there is a small chance that two threads will see the same object and wait.

For this reason any code analysers will give you a warning if you are synchronizing on a field which is not final.

Answer 2

It still releases the same monitor that was acquired, but any other code which also locks using myObject (impossible here as it's a local variable, making the synchronization fundamentally pointless) would start to use the new object.

Don't forget that synchronization is applied to objects (or rather, the monitors associated with objects) - not variables. The monitor being acquired/released just depends on the value of the expression when the start of the synchronized block is reached. The expression is not re-evaluated at the end of the synchronized block.