What is Java?
Java is a programming language. Applications written in Java require the Java Runtime to be installed on the system in order to run.
The Java version of Minecraft (as opposed to the Bedrock version) as well as some other applications rely on having a Java Runtime installed in order to function.
There are multiple distributions of Java available, but for AMP we recommend the Adoptium builds. This is what the AMP installation script uses on Linux.
Linux
On Linux systems, the AMP installer installs the correct version(s) of Java for you, however if you skipped this and wish to do it after the fact, you can run the following as root:
bash <(wget -qO- getamp.sh) installJava
As with the initial installation, do not put sudo in front of the command - instead run sudo su - first if you need to switch over from another user.
This will add the Adoptium repository to your system, and install the appropriate Java versions.
You will then need to restart your AMP instance or reboot your system for the new versions to be available for use in AMP itself.
Windows
Head to https://adoptium.net/ and download the latest LTS version. If you need older versions for any reason (which may be required by some older Minecraft servers for example) select the “Other platforms and versions” option to download the version applicable for your system.
After installing Java on Windows, a full reboot is required in order for AMP to detect the new installation.