You can manually split the String with
by counting characters and splitting at the right spot to keep the width under your desired character width. Give some leeway so if you get a big word, it won't still go to the next line.
Alternatively, you could use a JList to display your lines (instead of using
). That way, there's no way the line would split to the next line. However, if you do it that way, the user will click on the list like a list and not be able to select text like in a normal text pane.