If you wrap the tooltip in <html>
and </html>
tags, you can break lines with <br>
tags. See https://web.archive.org/web/20060625031340/http://www.jguru.com/faq/view.jsp?EID=10653 for examples and discussion. Main take-awy from that discussion: fButton.setToolTipText("<html><font face=\"sansserif\" color=\"green\">first line<br>second line</font></html>");
Or you can use the JMultiLineToolTip class that can be found many places on the net, including
https://github.com/ls-cwi/yoshiko-app/blob/master/src/main/java/com/yoshiko/internal/view/JMultiLineToolTip.java