Serialization and Deserialization In Java — What is SerialVersionUID and When to Regenerate It

Photo by Kodai Monma on Unsplash

Serialization and Deserialization In Java

Serialization is a mechanism of converting the state of an object into a byte stream.

Deserialization is the reverse process where the byte stream is used to recreate the actual Java object in memory.

This mechanism is used to help an object travel across a network and persist it.

Serialization/Deserialization — geeksforgeeks

To make a Java object serializable we implement the “” interface.

  • Only non-static data members are saved via serialization.
  • Static data members and transient data members are not saved (Make a non-static data member “transient” if you don’t want to save it).

The sequence of items in the stream:
- Class Name
- Class Modifiers (as 32 bit integer)
- Name of each interface (sorted by name)
- Each field (except private static/private transient, sorted by field name, as 32 bit integer)
- Class Initializer
- Each non-private constructor (sorted by name/signature)
- Each non-private method (sorted by name/signature)
- SHA-1 Algorithm
- Hash value from 1st and 2nd 32-bit values of SHA-1


A Serializable class can declare its own UID — serialVersionUID explicitly by declaring a field name that is static, final and of type long.

It is calculated based on the structure of your class — fields, methods, etc.

You should explicitly declare a serialVersionUID in your serializable class.
If not, JVM will generate one automatically.

serialVersionUID must be kept the same value for serialization and deserialization or an “InvalidClassException” will be thrown.

When to Regenerate?

This is stated detailed in “Java Object Serialization Specification”.

Incompatible Changes:
- Deleting fields
- Moving classes up/down in the hierarchy
- Changing non-static field -> static or non-transient -> transient
- Changing the declared type of primitive field
- Changing writeObject/readObject method
- Changing a class from Serializable -> Externalizable or Externalizable -> Serializable
- Changing a class from non-Enum type -> Enum or Enum -> non-Enum type
- Removing Serializable/Externalizable
- Adding writeReplace/readResolve

Compatible Changes
- Adding fields
- Adding/Removing classes
- Adding/Removing writeObject/readObject methods
- Adding
- Changing the access to a field
- Changing a field from static -> non-static or transient -> non-transient

How to generate serialVersionUID in IntelliJ IDEA

In IntelliJ IDEA -> Preferences, search for “Serializable class without ‘serialVersionUID’”.

Find “Serializable class without ‘serialVersionUID’”. Check it and select “Severity” level of your choice.

If you select “Error”, your class will give you an error same as below:

When you click on “Add ‘serialVersionUID’ field”, it will generate one for you:

Happy Coding!




I would love to change the world, but they won’t give me the source code | coding 👩🏼‍💻 | coffee ☕️ | jazz 🎷 | anime 🐲 | books 📚 | drawing 🎨

Love podcasts or audiobooks? Learn on the go with our new app.

Recommended from Medium

What I learned about Rust on my 4th of July Vacation this Year

Data Structures — When to Use Which

A Minute with EPNS - Week#34

BART — HackTheBox WriteUp

Mounting a Windows Shared Folder to a Docker container

Beginners guide to Sysdig Falco

Ubiquiti Edgeswitch 24 Port Switch with POE — SFP Lite

Ubiquiti Edgeswitch 24 Port Switch with POE - SFP Lite

Blocking And Nonblocking Assignment Synthesis

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store
Nil Seri

Nil Seri

I would love to change the world, but they won’t give me the source code | coding 👩🏼‍💻 | coffee ☕️ | jazz 🎷 | anime 🐲 | books 📚 | drawing 🎨

More from Medium

Lambda in Java

Factory Method Pattern 🏡

7 java tricky parts may probably face you as java developer

Difference Between map and flatMap in Java 8