In order to assign a superclass object in a variable to a subclass,one needs to do explicit casting.
For example:Person person=null;
Man man = (Man)person;
An automatic casting takes place when we typecast a object in subclass as parent class object.
Externalizable is coined as an Interface
It extends the Serializable Interface.
It also sends data into the Streams.
Externalizable sends data in a Compressed Format.
Externalizable is having two methods,for e.g. writeExternal(ObjectOuput out) & readExternal(ObjectInput in)