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Process of Serialization and Deserialization.

• One can save the state of an object within a file by a process of Serialization. The saved state of an object is called the serialized object, which includes the values of its instance variables.


• Post-serialization, you can transfer the file containing the serialized form of an object to its destination.


• At the destination, you can restore the object from its serialized form by a restoration process of Deserialization. The restored object and its instance variables will have the same value, which they had at the time of Serialization.

Methods used in Serialization and Deserialization

The process of "serialization" and "deserialization" is performed by using the methods of two high level stream classes, ObjectOutputStream and ObjectInputStream. These methods are -:

Methods	Description
writeObject()	This method of ObjectOutputStream class writes the state of an object to the stream, so that it can be saved within a file, and thus performing serialization.
readObject()	This method of ObjectInputStream class reads the saved object from a file in which the object's state was saved, and thus performing deserialization.

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Note :

• A class must implement "java.io.Serializable" interface in order to have its object's state saved by serialization and restored at the destination by deserialization.


• java.io.Serializable is a marker interface, with no field or method of its own.

Program with Serialization and Deserialization :

//Java - Example of Serialization and Deserialization 


import java.io.*;


//A class implementing Serializable interface 
class Serialz implements Serializable 	
{
int i=0;
public static void main(String... ar)
{
	Serialz ob= new Serialz();
	ob.i=10;	//object instance variable's value set to 10
	System.out.println("Before Serialization object has value : " + ob.i);
	try
	{
		FileOutputStream fos= new FileOutputStream("E:\\File.ser");//Saved state of the object is written to this file
		ObjectOutputStream oos= new ObjectOutputStream(fos);
		oos.writeObject(ob);	//Serializing, i.e. saving the state of this object, ob
		oos.close();
	}
	catch(Exception exp)
	{
		System.out.println(exp);
	}
	try	
	{
		FileInputStream fis= new FileInputStream("E:\\File.ser"); //Reading the same file for Deserialization
		ObjectInputStream ois= new ObjectInputStream(fis);
		ob = (Serialz)ois.readObject();	//Deserializing, i.e. restoring the object to its original state.
		ois.close();
		System.out.println("After Deserialization restored object has value : "+ ob.i);
	}
	catch(Exception exp	)
	{
	System.out.println(exp);
	}
}	//main method ends
}	//class definition ends

Output is -:

Before Serialization object has value : 10
After Deserialization restored object has value : 10

Program Analysis

In this code above, we are first performing the Serialization by calling the writeObject() method of ObjectOutputStream class, which saves the state of an object and its instance variable's value of int 10 in a file at path E:\\File.ser.

Mext, this serialized object is then deserialized by calling the readObject() method of ObjectInputStream class, which reads the serialized saved object, using which the original object is reconstucted with its instance variable having the same value 10, which it had at the time of Serialization.

Note :

The readObject() method returns the deserialized object, which is contained within an object of the Object class(the parent class of all Java classes). Hence, the casting of this deserialized object from Object type to its original type is required to reconstruct the original object.

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