Hi Shubha....what are trying to accomplish with this? If you want all actions of the class to be locked in a single
thread, then just modify all public methods of the class with synchronized. If you want a single instance of the class to be shared accross all other objects in your system, then declare the constructor protected and use static synchronized for all public methods and static for all protected/private methods and attributes.
As indicated above, the class itself cannot be "synchronized". But, the point is, whatever you are trying to do, there is a mechanism available to do it.