I need to create an AbsoluteLayout root and add the group at the specific position:
_root = iface.createRoot(new AbsoluteLayout(), SimpleStyles.newSheet(), layer);
_root.setSize(width(), height());
Group group = new Group(new AbsoluteLayout()).add(AbsoluteLayout.at(new Field("username"), 197, 337));
_root.add(AbsoluteLayout.at(group, 0, 0));