Sfdwhf

Solution found and implemented. See below original post.

My JVM installation apparently does not contain javaws.

$ sudo update-alternatives --get-selections | grep ^java

java                           manual   /usr/lib/jvm/java-12-oracle/bin/java

javac                          manual   /usr/lib/jvm/java-12-oracle/bin/javac

javadoc                        manual   /usr/lib/jvm/java-12-oracle/bin/javadoc

javap                          manual   /usr/lib/jvm/java-12-oracle/bin/javap

I have used both the PPA and a direct install from Oracle here with this documentation.

I need javaws to launch a jnlp file. The app apparently needs the Oracle distribution and not OpenJDK.

I tried v11 and v8 but PPA appears to be unavailable due to new licensing.

This is not a duplicate of not able to install javaws because webupd8team's PPA and oracle-java8-installer doesn't exist anymore due to new licensing:

javaws does not appear to be in the main v12 distribution as per the directory structure.

SOLUTION: Do not use ppa, Register for Oracle Network, download JDK8, install manually. javaws does not exist for v11+

Download:
https://www.oracle.com/technetwork/java/javaee/downloads/jdk8-downloads-2133151.html

Install JVM manually using:
https://linuxconfig.org/how-to-install-java-on-ubuntu-18-04-bionic-beaver-linux

Unfortunately Java Web Start is no longer included since Java 11 SE. Excerpt from Java Client Road Map (Update 2018-03-05):

Java Web Start has become a migration path for developers as browser
vendors continued to restrict plugin support over the past several
years.

Since it is predominantly a desktop technology,Web Start has some
limitations. In particular, it requires a standalone JRE to be
installed and maintained on the user’s desktop.

However, over the past decade,vendors of the most popular desktop
operating systems have emphatically pushed for applications on their
platforms to be delivered bundled with integrated, sandboxed runtimes.
Increasingly they require desktop applications to be distributed
through their own private "app stores".

The notion of an application being distributed separately from a
standalone JRE is,therefore,quickly fading.

Consequently:

• Oracle will extend support for Web Start in Java SE 8 from March, 2019, through at least March 2025.




• Oracle products that have dependencies on Web Start will remain on Java SE 8 and continue with the support timelines as indicated by
  those products.




• Oracle will not include Java Web Start in Java SE 11(18.9LTS)and later.




• Oracle will begin encouraging application developers and users to transition away from Java Web Start and encourage non-commercial
  consumers to remove any unused or non-supported Oracle JRE
  installations from their desktops.




• Developers who deploy desktop applications to individual consumers (eg, games, personal banking, or other B2C applications) will need to
  transition to other deployment technologies such as the jlink and/or
  third party packaging and deployment solutions before the end of 2020.




• Application developers who target applications for internal data processing, business, commercial, or production purposes, will either
  need to seek commercial license with Oracle, or transition to other
  deployment technologies by January 2019.

Therefore, if you really need Java Web Start you need to switch to Java 8.