I don't know if this been discussed before but there's a numerous amount of Johns in DC.
Here's a list of the Johns I can think of from the top of my head:
John Stewart (Green Lantern)
J'onn J'onzz (Martian Manhunter)
Jon Lane Kent
John Constatine
John Diggle
Johnny Thunder
Jonathan Kent
Are there any other Johns I should know about?