Unlike JTextArea, JTextPane has no option to turn line wrapping off. I found one solution to turning off line wrapping in JTextPanes,
The No Wrap Text Pane also provides an alternative solution that doesn't require wrapping the JTextPane in a JPanel, instead it overrides getScrollableTracksViewportWidth(). I prefer that solution, but it didn't quite work for me - I noticed that wrapping still occurs if the viewport becomes narrower than the minimum width of the JTextPane.
I found that JEditorPane is overriding getPreferredSize() to try and 'fix' things when the viewport is too narrow by returning the minimum width instead of the preferred width. This can be resolved by overriding getPreferredSize() again to say 'no, really - we always want the actual preferred size':
public class NoWrapJTextPane extends JTextPane {
@Override
public boolean getScrollableTracksViewportWidth() {
// Only track viewport width when the viewport is wider than the preferred width
return getUI().getPreferredSize(this).width
<= getParent().getSize().width;
};
@Override
public Dimension getPreferredSize() {
// Avoid substituting the minimum width for the preferred width when the viewport is too narrow
return getUI().getPreferredSize(this);
};
}