Summary

Around Java, the general-purpose programming language, the next LTS (Long Term Support) version of OpenJDK, 21, was released last month, on 17 Sep. 2023 🎉

On Debian 12 - bookworm repositories, the current version is 17 aka the previous LTS.

This post shows how to install 21 manually on Devuan 5 - Daedalus based on Debian 12.

Alternatively, JDK 21 "x64 Debian Package" Oracle offers is available.

In addition, Just in order to taste the latest, Oracle offers Java 21 PlayGround, too, which doesn't require local installation.

Moreover, one of the easiest ways is to use "OpenJDK" Docker Official Image and its "21-bookworm" tag.

Environment

OS: Devuan 5 Daedalus
- based on Debian 12 bookworm
App Engine: OpenJDK 21

Tutorial

Get OpenJDK package

Visit: https://jdk.java.net/21/

You can get it there. I used the command line below:

$ curl -LO https://download.java.net/java/GA/jdk21/fd2272bbf8e04c3dbaee13770090416c/35/GPL/openjdk-21_linux-x64_bin.tar.gz

You can verify the download by comparing the checksums between the server and the local. Use the command lines below, for example:

$ echo "$(curl -s https://download.java.net/java/GA/jdk21/fd2272bbf8e04c3dbaee13770090416c/35/GPL/openjdk-21_linux-x64_bin.tar.gz.sha256) openjdk-21_linux-x64_bin.tar.gz" | \
      sha256sum -c
openjdk-21_linux-x64_bin.tar.gz: OK

It means it was confirmed that the server checksum was equal to the local one:

$ # checksum of the downloaded file
$ sha256sum openjdk-21_linux-x64_bin.tar.gz
a30c454a9bef8f46d5f1bf3122830014a8fbe7ac03b5f8729bc3add4b92a1d0a  openjdk-21_linux-x64_bin.tar.gz

Place files

Extract it:

$ tar xzf openjdk-21_linux-x64_bin.tar.gz

The result is as below:

$ ls {.,jdk-21}
.:
jdk-21  openjdk-21_linux-x64_bin.tar.gz

jdk-21:
bin  conf  include  jmods  legal  lib  release

Now you have jdk-21 directory which contains bin etc. 👍

Set environment variables

Prepare PATH and JAVA_HOME.

As to PATH:

$ # case bash
$ export PATH=$(readlink -f ./jdk-21/bin):$PATH
$ # case fish
$ #set -x PATH $(readlink -f ./jdk-21/bin/):$PATH

As to JAVA_HOME:

$ # case bash
$ export JAVA_HOME=$(readlink -f .)
$ # case fish
$ #set -x JAVA_HOME $(readlink -f .)

Ready 🙌

Conclusion

Now Java 21 is in your hands:

$ java --version
openjdk 21 2023-09-19
OpenJDK Runtime Environment (build 21+35-2513)
OpenJDK 64-Bit Server VM (build 21+35-2513, mixed mode, sharing)

Let's do test run. Create a .java file:

$ nvim HelloWorld.java

Write below in it:

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, world.");
    }
}

The way to execute it directly is as below:

$ java HelloWorld.java
Hello, world.

Yay. Next, try to compile it manually and run it:

$ ls HelloWorld*
HelloWorld.java

$ javac HelloWorld.java
$ # .class file is generated

$ ls HelloWorld*
HelloWorld.class  HelloWorld.java

$ java HelloWorld
Hello, world.

Hello, the latest Java on the latest Devuan ☺

Java 21 on Devuan 5 (Debian 12): Install manually