Difference Between Serializable and Externalizable in Java Serialization

// Java Program to illustrate Serializable

// Importing utility classes
// Importing input output classes
import java.io.*;
import java.util.*;

// Main Class
// Class implementing serializable interface
class serializableDemo implements Serializable {
    
    // Member variables of this class
    String name;
    int age;
    int jobId;

    // Default constructor
    public serializableDemo(String name, int age, int jobId)
    {
        // This keyword is used to refer
        // current object instance
        this.name = name;
        this.age = age;
        this.jobId = jobId;
    }

    // Method 2
    // Main driver method
    public static void main(String[] args) throws Exception
    {

        // Creating an object of class in main() method
        serializableDemo t1
            = new serializableDemo("Ram", 34, 2364);

        // Serialization

        // Saving of object in a file
        FileOutputStream fos
            = new FileOutputStream("abc1.ser");
        ObjectOutputStream oos
            = new ObjectOutputStream(fos);

        // Method for serialization of object
        oos.writeObject(t1);

        System.out.println("Object has been serialized");
        // Deserialization

        // Reading the object from a file
        FileInputStream fis
            = new FileInputStream("abc1.ser");
        ObjectInputStream ois = new ObjectInputStream(fis);

        // Method for deserialization of object
        serializableDemo t2
            = (serializableDemo)ois.readObject();

        // Display message only
        System.out.println("Object has been deserialized ");

        // Print and display the name and age
        // to illustrate Serializable
        System.out.println("Name:" + t2.name + "\n"
                           + "Age:" + t2.age + "\n"
                           + t2.jobId);
    }
}

// Java Program to illustrate Externalizable

// Importing input output classes
import java.io.*;
// Importing utility classes
import java.util.*;

// Main Class
// Class implementing externalizable class
public class ExternalizableDemo implements Externalizable {

    // Member variables of this class
    String name;
    int age;
    int jobId;

    // Constructors of this class

    // Constructor 1
    // No-argument constructor
    public ExternalizableDemo()
    {

        // Display message
        System.out.println(
            "Public no-argument constructor");
    }

    // Constructor 2
    // Default constructor
    public ExternalizableDemo(String name, int age,
                              int jobId)
    {

        // This keyword refers to current object itself
        this.name = name;
        this.age = age;
        this.jobId = jobId;
    }

    // Implementing write external method
    public void writeExternal(ObjectOutput out)
        throws IOException
    {
        // Writing name and age to file
        out.writeObject(name);
        out.writeInt(age);
    }

    // Implementing readExternal method
    public void readExternal(ObjectInput in)
        throws IOException, ClassNotFoundException
    {
        // Reading name from file
        name = (String)in.readObject();

        // Reading age from file
        age = in.readInt();
    }

    // Main method
    public static void main(String[] args) throws Exception
    {

        // Creating an object of type ExternalizableDemo
        ExternalizableDemo t1 = new ExternalizableDemo("Ram", 35, 23675);

        // Serialization of object
        FileOutputStream fos = new FileOutputStream("abc.ser");

        ObjectOutputStream oos = new ObjectOutputStream(fos);

        oos.writeObject(t1);

        // Deserialization
        FileInputStream fis = new FileInputStream("abc.ser");

        ObjectInputStream ois = new ObjectInputStream(fis);

        ExternalizableDemo t2 = (ExternalizableDemo)ois.readObject();

        // Display message
        System.out.println("Name :"
                           + " " + t2.name + " "
                           + "Age :"
                           + " " + t2.age);
    }
}