Checklist

Before beginning check this list:

• You should use Maven 3.0.x or higher
• You should use a JDK 1.8 or higher. You should not use a JRE.
• Check the project nature, it should have a Maven nature and also it should recognize the language you are coding
• You should define a launcher as described here
• If you are using Maven, you should have a src/main/xxxx where xxxx is your language: java (for Java and Xtend), groovy, scala, etc.

Check this errors

java.lang.UnsupportedClassVersionError: ---Arena app--- : Unsupported major.minor version 51.0

JDK is 1.7 or lower. You must upgrade to a JDK 1.8 or higher version.

Error occurred during initialization of VM
java.lang.Error: java.lang.ClassNotFoundException: ....APOClassLoader

Probably Maven dependencies are not correctly downloaded. Check the %user/.m2/repository folder, or try a Maven > Update project (you can check the "force update snapshots" option).

Launch configuration references non-existing project celulares-ui-arena-scala

In this case you checked out a project with a different name, but the launcher still references the original project name. Either rename the project or change the launcher configuration.

Exception in thread "main" java.lang.RuntimeException: Esta aplicación no está corriendo con el ClassLoader necesario. Corra  la aplicación con el siguiente parámetro para la VM: -Djava.system.class.loader=org.uqbar.apo.APOClassLoader. El ClassLoader actual es: sun.misc.Launcher$AppClassLoader@6fd3633c
        at org.uqbar.arena.Application.validateClassLoader(Application.java:32)
        at org.uqbar.arena.Application.<init>(Application.java:24)

You are using a default Class Loader, use APOClassLoader instead (as described here)

"I'm not able to use <=> operator"

If you are programming in other language than Xtend, this won't work: you must use bindXXXX messages.

If you are programming in Xtend language, then you have a missing import as described here:

import static extension org.uqbar.arena.xtend.ArenaXtendExtensions.*