a line numbers list as separate panel which gets the line numbers from the text editor
a scroll pane which contains the text editor
a text editor
I'm planning on creating a new class for all that together. That means there will be 3 new classes when I'm finished working on this issue: a class for the editor pane as whole (EditorPane, obviously), a class for the line numbers (LineNumbersList) and a new text editor, based on the JTextPane(TextEditorPane).