Ok, the code runs and works as expected. OK. When you don't have the line "super(y)" the JVM tries to execute "super()" except that it can't find that. I expect if you add a constructor to your "Super" class with no args, then you can do what ever you want with it. If you remove the "int x" from the "Super" constructor that you have, it will call that constructor by default.
So, if you don't specify any constructor, a default one with no args and no code is produced. if you do specify one, a default one will NOT be produced.
I am really hoping this answers you question