Serialization:

 Serialization is a process of writing the state of an object to a byte stream.

 Serialization is also needed to implement Remote Method Invocation (RMI). RMI allows a Java object on one machine to invoke a method of a Java object on a different machine. An object may be supplied as an argument to that remote method. The sending machine serializes the object and transmits it. The receiving machine deserializes it.

 Assume that an object to be serialized has references to other objects, which, in turn, have references to still more objects. This set of objects and the relationship among them form a directed graph.

 If one attempt to serialize an object at the top of a graph, all the other referenced objects are recursively located and serialized.Similarly, during the process of deserialization, all of these objects and their references are correctly restored.

 The interfaces and classes that support serialization are as follows:

o   Serializable:Only an object that implements the Serializableinterface can be saved and restored by the serialization facility. The Serializable interface defines no members. It is simply used to indicate that the class can be serialized. If a class is Serializable, all of its subclasses are also Serializable.

Variables that are declared as transientare not saved by the serialization facility. Also, static variables are not saved.

o   Externalizable:The Java facilities for serialization and deserialization have been designed so that much of the work to save and restore the state of an object occurs automatically. There are situations in which the programmer may need to have control over these processes. For example, it may be desirable to use compression or encryption technique. The Externalizable interface is designed for these situations.

The Externalizableinterface defines two methods:

voidreadExternal(ObjectInputinStream) throws IOException, FileNotFoundException

voidwriteExternal(ObjectOutputoutStream) throws IOException

Here, inStream is a byte stream from which the object is to be read, and outStream is a byte stream