What is serialVersionUID and why specify it in Java?

Hi everyone! I'm writing a small Java application that saves user data to a file via serialization. I have a User class with fields name, age, and email. I implemented Serializable, and everything worked fine until I added a new field phone. After that, when trying to deserialize old files, I got an exception: java.io.InvalidClassException: User; local class incompatible: stream classdesc serialVersionUID = 123456789, local class serialVersionUID = 987654321 I read that I need to declare serialVersionUID, but I don't fully understand why it's needed and how to use it correctly. Here's my class: ```java import java.io.Serializable; public class User implements Serializable { private String name; private int age; private String email; // private