What is the difference between Serializable and Externalizable in Java?

Question

What is the difference between Serializable and Externalizable in Java?

Answer 1

The Externalizable interface was not actually provided to optimize the serialization process performance! but to provide means of implementing your own custom processing and offer complete control over the format and contents of the stream for an object and its super types!

Examples of this is the implementation of AMF (ActionScript Message Format) remoting to transfer native action script objects over the network.