I've downloaded OpenJDK 8 today via sudo apt-get install openjdk-8-jdk
and it seems like JavaFX is not included in it.
> java -version
openjdk version "1.8.0_66-internal"
OpenJDK Runtime Environment (build 1.8.0_66-internal-b17)
OpenJDK Server VM (build 25.66-b17, mixed mode)
I've installed E(fx)clipse in latest Eclipse (Eclipse Mars) too, but I'm still getting message javafx couldn't be resolved.
According to the packages list in Ubuntu Wily Xenial Bionic there is a package named openjfx. This should be a candidate for what you're looking for:
JavaFX/OpenJFX 8 - Rich client application platform for Java
You can install it via:
sudo apt-get install openjfx
It provides the following JAR files to the OpenJDK installation on Ubuntu systems:
/usr/lib/jvm/java-8-openjdk-amd64/jre/lib/ext/jfxrt.jar
/usr/lib/jvm/java-8-openjdk-amd64/jre/lib/jfxswt.jar
/usr/lib/jvm/java-8-openjdk-amd64/lib/ant-javafx.jar
/usr/lib/jvm/java-8-openjdk-amd64/lib/javafx-mx.jar
If you want to have sources available, for example for debugging, you can additionally install:
sudo apt-get install openjfx-source