Mike Slinn
ScalaCourses.com

Installing Scala Prerequisites

— Draft —

Published 2013-12-01. Last modified 2024-08-24.
Time to read: 4 minutes.

Discusses terminal emulators and installing a Java development kit (JDK) to power Scala.

Windows users should have already worked through Installing Windows Subsystem for Linux.

Install a Terminal Emulator

Because a lot of your work with Scala tools is via the command line, you should install a terminal emulator and get used to working with the keyboard, if you are not in that mode already. The bash shell is used for many code examples in this course. If you have zsh, then you can probably figure out any small changes if required to make the sample code work.

So Many Java; Much Confusion

TL;DR – Look for Temurin.

This topic became urgent when Oracle changed their licensing in such a way that most Java installers broke. This is to discourage most people from using Oracle Java. Temurin / Adoptium brand is a solid alternative.

The version of the JDK required to power Scala depends on the version of Scala you intend to use. For Scala 2.13, use Termurin 8 or 11, available for all operating systems here. The material in this course has been tested with many different Java brands for many different versions from 8 through 21. All have worked fine. Most Scala projects will work in production just fine on any currently maintained flavor.

As of 2024-08-16, Java 17 was used by the Scala developers, so if you have a choice, that might be the safest bet.

Java 11 support requires sbt 1.3+. Temurin 11 from Eclipse Adoptium, formerly known asOpenJDK, is the most tested version for Scala 2.13.

Sbt 1.3.0 is first release of sbt that’s been tested on JDK 11 extensively.
All integration tests on Travis CI are onOpenJDK’s JDK 11.
 – From Sbt 1.3.0 release notes

The main reason to switch from Java 8 to 11 is better support of Docker and Kubernetes; Java 11 has better support for running in containers because of resources management (memory and CPU limits). JDK 11 bases its memory settings on the Docker image limits and not the the global limits and won’t throw OOMException so frequently. There are also better GCs in Java 11+, for example ZGC.

Microsoft wrote a nice summary of the differences between JDK 8 and JDK 11.

Here is a table I’ve taken from docs.scala-lang.org:

In summary, JDK 8 works with Scala 2.11.0+, and JDK 21 works with 2.13.11+.

For Further Reading

Free JDKs

The following list are all based on Oracle OpenJDK. Azul summarized the differences here.

Install OpenJDK

As we’ve discussed, JDK version 8 or 11 is officially recommended for Scala 2.13. I have had no problems with JDK 17. Check the JDK version installed on your computer by typing this into a shell prompt:

Shell
$ java -version
openjdk version "17.0.11" 2024-04-16
OpenJDK Runtime Environment (build 17.0.11+9-Ubuntu-1)
OpenJDK 64-Bit Server VM (build 17.0.11+9-Ubuntu-1, mixed mode, sharing)

Now we’ll see how to install JDKs on Mac, Linux and Windows.

Mac

If you do not have Brew installed, install it by typing:

Shell
$ ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

$ brew update

Now you can use brew to install OpenJDK. To install the most recent JDK version, type:

Shell
$ brew untap AdoptOpenJDK/openjdk

$ brew install --cask temurin

Installing another JDK version:

Shell
$ brew tap homebrew/cask-versions

$ brew install --cask temurin8

You could also install other versions of OpenJDK:

Shell
$ brew install --cask temurin9
Shell
$ brew install --cask temurin11
Shell
$ brew install --cask temurin17

You can list the JDKs available on your Mac. Here is my collection of JDKs:

Shell
$ jenv versions
system
* 1.8 (set by /Users/mslinn/.jenv/version)
  1.8.0.111
  12.0
  12.0.1
  openjdk64-12.0.1
  oracle64-1.8.0.111

If you have a JDK that jenv does not know about, you can manually add specific JDKs to jenv:

Shell
$ jenv add /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home

You can use jenv to set any JDK to be active:

Shell
$ jenv global 1.8

$ java -version
java version "1.8.0_111"
Java(TM) SE Runtime Environment (build 1.8.0_111-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.111-b14, mixed mode)

Debian, Ubuntu and Windows Subsystem for Linux

This is an interesting option for installing Java on Ubuntu / WSL.

Shell
$ yes | sudo apt install --no-install-recommends default-jdk

This information about Debian and Ubuntu is also applicable to WSL because its default guest Linux image is Ubuntu. You could use Oracle’s Linux instructions to install their JDK, but I recommend that you wean yourself away from Oracle’s JDK now. It is better to use apt for system maintenance. The Debian Wiki has a really good article on apt.

Shell
$ sudo apt install openjdk-8-jdk

Check to see how many versions of Java exist on your system. For the various Linux distributions, the directories that Java is installed into vary widely, however Ubuntu and other Debian offshoots often uses subdirectories of /usr/lib/jvm, for example /usr/lib/jvm/java-8-oracle.

Shell
$ sudo update-alternatives --config java
There is 1 choice for the alternative java (providing /usr/bin/java).

  Selection    Path                                     Priority   Status
------------------------------------------------------------
  0            /usr/lib/jvm/java-8-oracle/jre/bin/java   1081      auto mode
* 1            /usr/lib/jvm/java-8-oracle/jre/bin/java   1081      manual mode

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

Now confirm that the proper version of Java is set as the default:

Shell
$ java -version
java version "1.8.0_111"
Java(TM) SE Runtime Environment (build 1.8.0_111-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.111-b14, mixed mode)

Native Windows

This is not a good idea. Native Windows is a horrible development environment for Scala. Really, really bad. Don’t do this!

Instead, install Windows Subsystem for Linux (WSL) and follow the instructions above for Ubuntu.

If you enjoy suffering for no reason, you can install OpenJDK for Windows x64 for Windows x64 from here.

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