Working with Multiple Versions of Java on Ubuntu

Today I encountered a bug that was specific to JDK 16 on a project I was working on, and I needed to switch back my Java version to something older. I realized I had forgotten (once again) how to switch between multiple Java version on Ubuntu (Debian), so I’ve decided to write a short article that would help me remember this better.¹

You can install easily multiple version of Java on Ubuntu via apt:

$ sudo apt install openjdk-8-jdk openjdk-8-source openjdk-8-doc
$ sudo apt install openjdk-11-jdk openjdk-11-source openjdk-11-doc

Typically the newest version of Java you install will become the default, but you can easily change this:

$ sudo update-alternatives --config java
There are 2 choices for the alternative java (providing /usr/bin/java).

  Selection    Path                                          Priority   Status
------------------------------------------------------------
  0            /usr/lib/jvm/java-11-openjdk-amd64/bin/java   1111      auto mode
* 1            /usr/lib/jvm/java-11-openjdk-amd64/bin/java   1111      manual mode
  2            /usr/lib/jvm/java-8-openjdk-amd64/bin/java    1081      manual mode

Press <enter> to keep the current choice[*], or type selection number:

Notice that pressing 0 mean “auto-select the newest Java available” (in our case Java 11). You can now select Java 8 by pressing 2 and verify the command worked properly like this:

$ java -version
openjdk version "1.8.0_292"
OpenJDK Runtime Environment (build 1.8.0_292-8u292-b10-0ubuntu1~20.04-b10)
OpenJDK 64-Bit Server VM (build 25.292-b10, mixed mode)

You’ll need to repeat the above steps for javac (the Java compiler binary) as well:

$ sudo update-alternatives --config javac

This much I already knew, even if I keep forgetting the exact name of update-alternatives, but today I learned something new as well. You can actually simplify the process a bit by using the specialized command update-java-alternatives:

$ update-java-alternatives -l
java-1.11.0-openjdk-amd64      1111       /usr/lib/jvm/java-1.11.0-openjdk-amd64
java-1.8.0-openjdk-amd64       1081       /usr/lib/jvm/java-1.8.0-openjdk-amd64

$ sudo update-java-alternatives -s java-1.11.0-openjdk-amd64

Quite handy! You can also go back to the latest Java version with a shorthand:

$ sudo update-java-alternatives -a

-a stands for --auto, meaning the Java version with highest priority (in our case Java 11 with priority 1111).

That’s all I have for you today. Short and sweet!