Serialization object graph

package myio;

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

class Dog1 implements Serializable
{
Cat c=new Cat();
}
class Cat implements Serializable
{
    int i=10;
Rat r=new Rat();
}
class Rat implements Serializable
{
int j=20;
}

class SerDemo2
{
public static void main(String arg[])throws Exception
{
Dog1 d=new Dog1();
FileOutputStream fos=new FileOutputStream("abc1.txt");
ObjectOutputStream oos=new ObjectOutputStream(fos);
oos.writeObject(d);
FileInputStream fis=new FileInputStream("abc1.txt");
ObjectInputStream ois=new ObjectInputStream(fis);
Dog1 d1=(Dog1)ois.readObject();
System.out.println(d1.c.i);
System.out.println(d1. c.r.j);
}
}

output:
10
20