Fix Java Version Errors on Minecraft Servers

The Error

If you see UnsupportedClassVersionError or has been compiled by a more recent version of the Java Runtime (class file version 65.0) when starting your Minecraft server, your installed Java version is too old for the server jar. This is the most common minecraft java version error fix scenario.

Java Version Requirements by Minecraft Version

Minecraft Version	Minimum Java	Recommended Java
1.21+	Java 21	Java 21 (Temurin/Adoptium)
1.18, 1.20.6	Java 17	Java 17 or 21
1.17	Java 16	Java 17
1.12, 1.16.5	Java 8	Java 8 or 11

Class file version numbers map to Java releases: 65 = Java 21, 61 = Java 17, 60 = Java 16, 52 = Java 8. The error message tells you exactly which version is needed.

Installing the Correct Java Version

Debian / Ubuntu

# Add Adoptium repository
sudo apt install -y wget apt-transport-https gpg
wget -qO, https://packages.adoptium.net/artifactory/api/gpg/key/public | gpg --dearmor | sudo tee /etc/apt/trusted.gpg.d/adoptium.gpg
echo "deb https://packages.adoptium.net/artifactory/deb $(lsb_release -cs) main" | sudo tee /etc/apt/sources.list.d/adoptium.list
sudo apt update
sudo apt install temurin-21-jre

CentOS / RHEL / Fedora

sudo yum install java-21-openjdk

Windows

Download the Temurin 21 installer from adoptium.net and run it. Make sure to check "Set JAVA_HOME" during installation.

Managing Multiple Java Versions

If you run multiple servers on different Minecraft versions, you need multiple Java installations. On Linux:

# List installed alternatives
sudo update-alternatives --config java

# Or use the full path in your start script:
/usr/lib/jvm/temurin-21-jre/bin/java -Xmx4G -jar paper.jar nogui

Using the full path is the most reliable approach, it avoids any ambiguity about which Java runs your server.

Hosting Panel Users

If you use a game hosting panel (Pterodactyl, Multicraft, etc.), look for a "Java Version" or "Docker Image" selector in your server settings. Select the image that includes Java 21 for Minecraft 1.21+. If your panel does not offer Java 21, contact your hosting provider, they need to update their images.

Verifying the Fix

After installing the correct Java version, run:

java -version

You should see output like openjdk version "21.0.x". Then start your server again. The minecraft java version error fix is complete when the server boots without class version errors.

If the server still won't start after fixing Java, check our general startup troubleshooting guide.

Need reliable hosting that handles these issues out of the box? Astroworld Hosting runs optimised Paper servers on NVMe SSDs with 24/7 support.

Questions about Fix Java Version Errors

Why would you set up Fix Java Version Errors at all?

If you see UnsupportedClassVersionError or has been compiled by a more recent version of the Java Runtime (class file version 65.0) when starting your Minecraft server, your installed Java version is too old for the server jar.

What separates the options in Fix Java Version Errors?

For 1.21+, the table on this page lists Minimum Java: Java 21, Recommended Java: Java 21 (Temurin/Adoptium).

What does this guide say about java version requirements by minecraft version?

This is the most common minecraft java version error fix scenario.

Fix Java Version Errors: what does installing the correct java version mean here?

Class file version numbers map to Java releases: 65 = Java 21, 61 = Java 17, 60 = Java 16, 52 = Java 8.