What is the purpose of the Serializable interface?

Question

Example of implementation:

 public class MyClass implements Serializable{
     private static final long serialVersionUID = 1L;
 }

Answer 1

Serialization means saving the current state of the objects in binary format to your computer, so this state can be recovered later by recreating the object in memory just as it was at the time of its serialization.

See illustration:

Source: State of the art - Nuances about serialization of heritage objects in Java

In order to be able to serialize and deserialize an object, it is mandatory that your class implements the interface Serializable.

An example of a code that serializes an object:

import java.io.*;

public class SerializeDemo
{
   public static void main(String [] args)
   {
      Employee e = new Employee();
      e.name = "Reyan Ali";
      e.address = "Phokka Kuan, Ambehta Peer";
      e.SSN = 11122333;
      e.number = 101;

      try
      {
         FileOutputStream fileOut =
         new FileOutputStream("/tmp/employee.ser");
         ObjectOutputStream out = new ObjectOutputStream(fileOut);
         out.writeObject(e);
         out.close();
         fileOut.close();
         System.out.printf("Serialized data is saved in /tmp/employee.ser");
      }catch(IOException i)
      {
          i.printStackTrace();
      }
   }
}

Deserializing the same object:

import java.io.*;
public class DeserializeDemo
{
   public static void main(String [] args)
   {
      Employee e = null;
      try
      {
         FileInputStream fileIn = new FileInputStream("/tmp/employee.ser");
         ObjectInputStream in = new ObjectInputStream(fileIn);
         e = (Employee) in.readObject();
         in.close();
         fileIn.close();
      }catch(IOException i)
      {
         i.printStackTrace();
         return;
      }catch(ClassNotFoundException c)
      {
         System.out.println("Employee class not found");
         c.printStackTrace();
         return;
      }
      System.out.println("Deserialized Employee...");
      System.out.println("Name: " + e.name);
      System.out.println("Address: " + e.address);
      System.out.println("SSN: " + e.SSN);
      System.out.println("Number: " + e.number);
    }
}

Upshot:

Deserialized Employee...
Name: Reyan Ali
Address:Phokka Kuan, Ambehta Peer
SSN: 0
Number:101

Source: Tutorials Point

Answer 2

It gives the class the ability to produce a format in which the object data is used externally to the code, in general it is persisted in some form of temporary or permanent storage or is transmitted to another resource.

This format can be text or binary in several standard or proprietary variants. It is very common to use JSON or XML.

Deserialization is the opposite process. Take data in a known format and place the data found in the serialized state within the class members by creating or updating an object.

Implementing this interface is not very trivial, although it seems to be. It is common to use a ready-made solution that uses reflection. It is common to serialize expose private parts of the class, which is often not desirable, so need care, on the other hand without private parts may not have all that is needed.

Answer 3

Adding the serializable interface makes it possible to transform the object into a format that can be saved in a file. For example, to use an Objectoutputstream and save an object to a disk file you will need to implement this interface.