[SOLVED] Getting the bounds of the text inside a jlabel

Getting the bounds of the text inside a jlabel

I want to draw an arrow from the text in a JLabel to a point outside the JLabel. To start the arrow at an appropriate place, I need the bounds of the actual text inside the JLabel. My answer below will show how to get those bounds.

Solution

To get the bounds of text in a JLabel, we need the accessible context, a protected field. So we extend JLabel. The accessible context only knows about the text if it is HTML, so I prepend "<html>" in the constructor; a more general version would first check to see if the text already begins with that string.

   class FieldLabel extends JLabel {
        FieldLabel(String text) {
            super("<html>"+text);
        }
        Rectangle getTextBounds() {
            JLabel.AccessibleJLabel acclab 
                = (JLabel.AccessibleJLabel) getAccessibleContext();
            if (acclab.getCharCount() <= 0)
                return null;
            Rectangle r0 = acclab.getCharacterBounds(0);
            Rectangle rn = acclab
                .getCharacterBounds(acclab.getCharCount()-1);

            return new Rectangle(r0.x, r0.y, 
                    rn.x+rn.width-r0.x, Math.max(r0.height, rn.height));
        }
    }

Other solutions have the potential advantage of not creating three new Rectangle objects per call. This could be a problem if getTextBounds is called in a MouseMoved event listener. At some cost in complexity, the final Rectangle could be cached along with the JLabel width and height.