In response to the article "Why use SerialVersionUID inside the Serializable class in Java"

So.. We have a class that we want to serialize using conventional methods (we use Serializable)

package Serialization;

import java.io.Serializable;

public class SerializableClass implements Serializable {
    private String name;
    private int number;
 }

We are writing a test application. I’ll say right away that my goal is to show what serialVersionUID.

package Serialization;

import java.io.*;

public class MainSerializable {
    final static String FILE_NAME = "c:\\File.dat";

    public static void serialize(Object object) throws IOException {
        FileOutputStream fileOutputStream = new FileOutputStream(FILE_NAME);
        ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream);

        objectOutputStream.writeObject(object);

        fileOutputStream.close();
        objectOutputStream.close();
    }

    public static Object deserialize() throws IOException, ClassNotFoundException {
        FileInputStream fileInputStream = new FileInputStream(FILE_NAME);
        ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);

        Object object = objectInputStream.readObject();

        objectInputStream.close();

        return object;
    }

    public static void main(String[] args) throws IOException, ClassNotFoundException {
        SerializableClass serializableClass = new SerializableClass();

        serialize(serializableClass);

        SerializableClass newObject = (SerializableClass) deserialize();
    }
}

Everything works great. The class is serialized to a file FILE_NAME = "c:\\File.dat". It was getting dark... :) Forgot to add fields to the class. Add:

public class SerializableClass implements Serializable {
    private String name;
    private int number;
    private String FirstName;   // +
    private String LastName;    // +
 }

Everything seems to be fine.. everything compiles.. So we run it main, deserialize the class SerializableClassfrom the file " c:\\File.dat":

    public static void main(String[] args) throws IOException, ClassNotFoundException {
        SerializableClass newObject = (SerializableClass) deserialize();
    }

Oh... What to do...

Exception in thread "main" java.io.InvalidClassException: Serialization.SerializableClass; local class incompatible: stream classdesc serialVersionUID = 8129437039424566964, local class serialVersionUID = -8271479231760195917
	at java.base/java.io.ObjectStreamClass.initNonProxy(ObjectStreamClass.java:689)
	at java.base/java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1903)
	at java.base/java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1772)
	at java.base/java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
	at java.base/java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1594)
	at java.base/java.io.ObjectInputStream.readObject(ObjectInputStream.java:430)
	at Serialization.MainSerializable.deserialize(MainSerializable.java:22)
	at Serialization.MainSerializable.main(MainSerializable.java:30)

In general, everything is fair. The class has changed and its serialVersionUID= -8271479231760195917, and serialized in the file serialVersionUID= 8129437039424566964. What to do now, what to do? How to create an instance? There is an exit. We need to declare in our class: static final long serialVersionUID, which is equal to serialVersionUIDthe grayed out :) class in the file. Those. we said, go ahead, I’ll deserialize.. you can.. your versions are the same:

package Serialization;

import java.io.Serializable;

public class SerializableClass implements Serializable {
    static final long serialVersionUID = 8129437039424566964L;

    private String name;
    private int number;
    private String FirstName;   // +
    private String LastName;    // +
}

We launch... And.. Everything works. As I understand, this error could have been avoided if the class had declared in advance:

public class SerializableClass implements Serializable {
    static final long serialVersionUID = 1L;

    private String name;
    private int number;
}

Those. we don't let Java do its own calculations serialVersionUIDbased on its algorithms (quite complex algorithms). Now, whenever a class changes, we serialVersionUID = 1L check:

    public static void main(String[] args) throws IOException, ClassNotFoundException {
        SerializableClass serializableClass = new SerializableClass();

        serialize(serializableClass);

        SerializableClass newObject = (SerializableClass) deserialize();
    }

It works.. And now like this:

public class SerializableClass implements Serializable {
    static final long serialVersionUID = 1L;

    //private String name;
    //private int number;
}

Yes.. And so?

public class SerializableClass implements Serializable {
    static final long serialVersionUID = 1L;
    public int A;
    protected String value;
    //private String name;
    //private int number;
}

Cool.. everything continues to work. So I finished my first article. I wanted to put all this in the comments, but I couldn’t get through the symbols. I will accept sober criticism and comments PS Thanks to the author who inspired me to do these delights.. Probably, this is how they learn :) Good luck to everyone :)