The Externizable interface extends the serializable interface.
When you use Serializable interface, your class is serialized automatically by default. But you can override writeObject() and readObject()two methods to control more complex object serailization process.
When you use Externalizable interface, you have a complete control over your class's serialization process. The two methods to be implemented are :
void readExternal(ObjectInput)
The object implements the readExternal method to restore its contents by calling the methods of DataInput for primitive types and readObject for objects, strings and arrays.
void writeExternal(ObjectOutput)
The object implements the writeExternal method to save its contents by calling the methods of DataOutput for its primitive values or calling the writeObject method of ObjectOutput for objects, strings, and arrays.
