synchronized object set to null

I have two threads Thread1 and Thread2

//Within Thread1     
synchronized(obj1)  
{  
    obj1 = null;  
}  

//Within Thread2  
synchronized(obj1)  
{  
    do something  
}   

If jvm first executes thread1 and sets obj1 to null, then will thread2 see that change immediately or will it take time and jvm could still run the thread2 synchronized block since obj1 is not yet null?