Can't Run Hello World program in Tornadofx - kotlin

Question

I'm using Ubuntu Mate 16.04 and I'm trying to run a simple hello world program using tornadofx. The file is called hello.kt and I'm attempting to compile and run it using just the terminal.
It seems to compile just fine by running
kotlinc -cp tornadofx.jar hello.kt -include-runtime -d hello.jar
But when I try to run it by entering
java -jar hello.jar
I get a NoClassDefFoundError error:
Exception in thread "main" java.lang.NoClassDefFoundError: tornadofx/View
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:467)
at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
at java.net.URLClassLoader$1.run(URLClassLoader.java:368)
at java.net.URLClassLoader$1.run(URLClassLoader.java:362)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:361)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at HelloKt.main(hello.kt:15)
Caused by: java.lang.ClassNotFoundException: tornadofx.View
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 13 more
Here's the file:
import javafx.scene.control.Label
import javafx.scene.layout.HBox
import tornadofx.App
import tornadofx.View
class HelloWorld : View() {
override val root = HBox(Label("Hello world!"))
}
class HelloWorldApp : App() {
override val primaryView = HelloWorld::class
}
fun main(args: Array<String>) {
val window = HelloWorldApp()
}
Any help would be greatly appreciated. Thanks.

Answer 1

You need to install Oracle JDK, which comes with JavaFX, or install the JavaFX OpenJDK bundles in Ubuntu. I would recommend the Oracle JDK.
Additionally, JavaFX Applications has to be launched, you can't simply instantiate the App class. See below.
The syntax in your example code is very outdated - did you find this in the guide or somewhere else? This is the current syntax for your code example, including the correct launch command.
class HelloWorld : View() {
override val root = hbox(label("Hello world!"))
}
class HelloWorldApp : App(HelloWorld::class)
fun main(args: Array<String>) {
launch<HelloWorldApp>(args)
}