Why a serialized object is different from the original?

Question

I try to create a program to compare 2 objects. If I create 2 instances of the same object, the 2 objects are differents because, even if they have the same "tin", they are 2 individuals objects.

But, in my case, I create an object, serialize it, deserialize it into a second instance and compare the original with the copy.

Why are they different ? I don't even use "new" to create the second instance. I just read the serialized object... Here are the 2 classes I use :

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class Main {

public static void main(String[] args) {
    File file = new File("something.serial");

    //Creation of the 1st object
    Something obj1 = new Something();

    //Serialization
    ObjectOutputStream oos;
    try {
        oos= new ObjectOutputStream(
                new BufferedOutputStream(
                        new FileOutputStream(file)));
        oos.writeObject(obj1);
        oos.close();
    } catch (IOException e) {
        e.printStackTrace();
    }

    //Second object
    Something obj2=null;

    //Deserialization
    ObjectInputStream ois;
    try {
        BufferedInputStream bis = new BufferedInputStream(
                new FileInputStream(file));
        ois = new ObjectInputStream(bis);
        obj2=(Something)ois.readObject();
        ois.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    }

    //Compare
    if (obj1.equals(obj2)) {
        System.out.println("Same");
    } else {
        System.out.println("Different : ");
        System.out.println(obj1.toString()+" - "+obj2.toString());
    }
}
}

and :

import java.io.Serializable;

public class Something implements Serializable {

/**
 * 
 */
private static final long serialVersionUID = 1L;
public int value = 2;

Something () {

}
}

Thank you for all your answers that will help me to understand.

how do you implement the equals method in your Something class? If you don't override it at all it doesn't compare your objects correctly obviously and equals returns false. — xander, Mar 28 '17 at 06:34
Your problem is that you don't understand what **equals()** really does. Therefore: learn about that; and then implement your own equals() method. — GhostCat, Mar 28 '17 at 06:40

score 4 · Accepted Answer · edited Mar 28 '17 at 06:37

well, when u serialize it, the state of the object is being saved to a file, not the memory location. When you deserialize it, a new object with the same state is being created internally and a reference to it is being passed to you.

As you have not overridden the equals() method, it is checking only if the memory address is the same.

Override the .equals() method and check whether the states are same yourself.

Why a serialized object is different from the original?

1 Answers1