Simple thing i did to get it working:
Went in eclipse > Window > Preferences
(Optional)typed in the search box "file" to help trim the tree of options. Went to General > Editors > File associations.
Clicked the ".class" type. Below there were 2 editors present, i clicked on the "Class File Editor" - the one with the icon from JD, clicked the "Default" button on the right.
Done. Now all ur class are belong to us.