java seriliazable

java seriliazable

1. serializable default serialize all field and object net.
2. Externalizable default deserialize all fields and use writeExternal and readExternal to serialize object. should provide public construct.
3. serializable interface use private writeObject and private readOjbect to implemnets the same fucntion as Extenalizable interface. (writeDefautObject and readDefaultObject).
4. Externalizable extends serializable