Object Graphs

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• Whenever we serialize an object, the set of all objects which are reachable from that object will be serialized automatically.  This group of objects are called object graph.
• In the object graph every object should be Serializable otherwise, NotSerializableException will come.

Example:

package com.javamonkeys.serialization;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

class User implements Serializable{
 UserDetails ud = new UserDetails();
}
class UserDetails implements Serializable{
 UserAddress ua = new UserAddress();
}
class UserAddress implements Serializable{
 int uaId=10;
}
public class ObjectGraphExample {
 public static void main(String[] args)throws IOException, ClassNotFoundException {
  User user = new User();
  FileOutputStream fiOutputStream = new FileOutputStream("D:\\serializablefile.ser");
  ObjectOutputStream oStream = new ObjectOutputStream(fiOutputStream);
  oStream.writeObject(user);
  
  FileInputStream fileInputStream = new FileInputStream("D:\\serializablefile.ser");
  ObjectInputStream oInputStream = new ObjectInputStream(fileInputStream);
  User usr = (User)oInputStream.readObject();
  System.out.println(usr.ud.ua.uaId);
 }

}

Note: In the above example User, UserDetails and UserAddress should be serialized otherwise we will get NotSerializableException.