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Employee.java

import java.io.*;

 

class Employee implements Externalizable{

 

  String ename;

  int age;

  double salary;

 

    //0-arg constructor

    public Employee()    {

        System.out.println("Employee()");

    }

 

    //parameterized constructor

    public Employee(String name, int age, double salary) {

        System.out.println("Employee(-,-,-)");

        ename = name;

        this.age = age;

        this.salary = salary;

    }

 

    //Just prints everything

    public String toString() {

        return "Emp Name::"+ename+" Emp Age::"+age+"

                    Emp Sal::"+salary;

    }

 

    //Here we have serialized only 2 properties,we have not serialized salary

    public void writeExternal(ObjectOutput out) throws IOException  {

        out.writeObject(ename);

        out.writeInt(age);

    }

    //Here we have mentioned what we want to deserialize,I am intrested to deserialize only ename

    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {

        ename = (String) in.readObject();//it will be deserialized and stored in ename property

    }

 

}

 ExternalizableDemo.java

public class ExternalizableDemo {

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

 

        //parameterized constructor is called

        Employee emp=new Employee("Satya",23,15000.00);

 

        //Serialization process

        FileOutputStream fos = new FileOutputStream("d:/myFile.txt");

        ObjectOutputStream oos = new ObjectOutputStream(fos);

        oos.writeObject(emp);

        oos.flush();

        oos.close();

 

        // Object deserialization

        FileInputStream fis = new FileInputStream("d:/myFile.txt");

        ObjectInputStream ois = new ObjectInputStream(fis);

 

        //0-args constructor is called

        Employee emp2 = (Employee)ois.readObject();

        ois.close();

        System.out.println("Details ::: " + emp2);  //toString() is called,which prints the details

        //Note that only name is deserialized

    }

}//class

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Note :-
To create Employee object,we are using parameterized constructor,
But to deserialize,JVM automatically looks for 0-args constructor.

Hope this article proves to be valuable one.
Any query/mistakes,we would like to hear from you.