First Java SE 1.4 reached its end of service life (obsolete). So for submission it's either v5 or v6. The good thing that it works for v5 is it's backward compatible - this means your code doesn't use any thing that is "since 1.6" accordingly to the API docs. One of these is java.awt.Component.setBounds().
Yet you should do your testing with v6 and say v6 in your version.txt file.