The string is not rendered properly for Vertical - JProgressBar. Even default strings like 100%, is not rendered in the JProgressBar. The preferred-width calculation has to be fixed.

Also its noted that the String is rendered as horizontal, even though the JProgressBar is vertical. For all other LAFs the string is rendered vertical for vertical JProgressBar.

Refer to attached screenshot.
Compile and run JProgressBarTest.java in GTK LAF