Yes we can use object as the key 

person p = new person();

HashMap m = new HashMap()
m.put(p,"mysqlf");
above works perfectly fy9 ..... but dont try to use the same
object as key twice :-)

yes, we can place any object as key value but that object
must and should implement the hashcode method.

Hi Ramarao,
Its not necessary to override hashCode() since hashcode is
default generated for every object. Please try my example n
check it by urself