Argthtjtr

I checked that the interface of

Serializable

Has no function definition, yet when I define

private void readObject(ObjectOutputStream oos){

    System.out.println("readObject!!");

}

private void writeObject(ObjectOutputStream oos){

    System.out.println("writeObject!!");

}

function in a class, they're called while object is being serialized.

This is odd to me, if the interface defines these 2 functions, then I should override them to make sure they're called.

But in Serializable, how does compiler generate code that if I define my own "writeObject"/"readObject", they're called while serialization?

I tried to append

@Override

annotation on top of both functions, compiler reports error.

So how it works at all, would you help to give some explanations?

Thanks a lot!

java.io.Serializable is a functional interface, so that means it doesn't define any methods in it. @Override annotation is put if only you really wanna make sure noone will try to modify your overridden method. The reason you got a compiler error on @Override is that there is no such method in Serializable, but instead you can find them in ObjectInputStream and ObjectOutputStream (which use as a low-level classes FileInputStream and FileOutputStream respectively).
If you really wanna do Serialization on let's say, a list, you can do it like this:

package Chaper8.IO;



import java.io.*;



import java.util.*;



public class Serialization_Deserialization {



public static void main(String  args){



    /*

     *  try-catch with resources, JVM makes sure to close the resources after you've finished using it

     * much easier than using finally and getting an exception for each resource closed

     * 

     */

    try(FileOutputStream out = new FileOutputStream("C:\Users\Andrei\Desktop\Exemple\worker.txt");

        ObjectOutputStream oos = new ObjectOutputStream(out);



        FileInputStream in = new FileInputStream("C:\Users\Andrei\Desktop\Exemple\worker.txt");

        ObjectInputStream ois = new ObjectInputStream(in);){



        //instances of the Worker class

        Worker w1 = new Worker("Worker1", 123456 , 2000.5);

        Worker w2 = new Worker("Worker2", 765436, 1500.15);

        Worker w3 = new Worker("Worker3", 364582, 1700.45);

        Worker w4 = new Worker("Worker4", 878234, 2100.34);

        ArrayList<Worker> list = new ArrayList<>();



        //just adding the persons in the list

        list.add(w1);

        list.add(w2);

        list.add(w3);

        list.add(w4);





        System.out.println("Doing serialization");

        oos.writeObject(list);



        System.out.println("Doing deserialization");

        ois.readObject();



    }catch(IOException | ClassNotFoundException e){

            e.printStackTrace();

    }

}

} 

Worker.java

/*

 *  Worker class, basic type with variables, constructor, and toString() overridden

 *  Here I have implemented Serializable for the reason that I need to make sure that

 *  I will serialize the object within the class

 *

 *  Note that I used transient for id. transient is a special keyword which makes sure 

 * that id will not be serialized, used for security reasons.

 * 

 *  serialVersionUID is another variable which is used during deserialization 

 * to verify that the sender and receiver of a serialized object have loaded 

 * classes for that object that are compatible with respect to serialization. 

 *  Throws InvalidClassException if the object has a different serialVersionUID

 * than that of the corresponding sender's class.

 *  

 */



import java.io.*;

class Worker implements Serializable{



private static final long serialVersionUID = 1L;

private String name;

private transient int id;

private double wage;



public Worker(String name, int id, double wage){

    this.name = name;

    this.id = id;

    this.wage = wage;

}

public String toString(){

    return "Person with name " +

    name + " and with id " +

    id + " has a salary of " + wage + "$";

    }

}