Dealing with level editor and game

I am already making a platform game engine (game and level editor) using java. So I want a JFrame, JMenuBar, JToolBar... for the level editor, and just JFrame for the game. So what's way to make it. Is it to create 1 frame for the game and another one for the editor? Or the same frame and change the components inside it? Or to make an external level editor and use exported files in game?