From the JavaDocs for ResourceBundle.getBundle(String baseName)
:
baseName
- the base name of the resource bundle, a fully qualified class name
What this means in plain English is that the resource bundle must be on the classpath and that baseName
should be the package containing the bundle plus the bundle name, mybundle
in your case.
Leave off the extension and any locale that forms part of the bundle name, the JVM will sort that for you according to default locale - see the docs on java.util.ResourceBundle for more info.