When a class implements a marker interface, then the object
of that class is given with a special behavior. For example
if a class implements remote interface(available in
java.rmi.* package) object of that class acts as a Remote
Object. For this reason java provides Marker Interface.

Marker interfaces can create an environment.

Marker interfaces are used to specify that a class belongs 
to a logical family or grouping - as quoted above, 
Cloneable is used to indicate that a particular class can 
be cloned, or Serializable is used to indicate that a 
particular class can be serialized.

when class implements marker interface our class object
getting special behavoiur.
EX:-
suppose our class implements java.lang.Serializible 
interface our class object getting special behaviour(our
class object converting java support format object to
network support)

Another Example our class implements java.rmi.Remote
interface our class object acts as Remote object.