Here is the documentation and implementation of CompoundBorder.isBorderOpaque:

    /**
     * Returns whether or not this compound border is opaque.
     * Returns true if both the inside and outside borders are
     * non-null and opaque; returns false otherwise.
     */
    public boolean isBorderOpaque() {
return (outsideBorder == null || outsideBorder.isBorderOpaque()) &&
               (insideBorder == null || insideBorder.isBorderOpaque());
    }

The implementation was made this way by the fix to bug 4317988 in merlin. However, as you can see, the documentation clearly does not match the implementaion any more. Considering the use of this class and it's other methods, it appears that the implementation is correct and it is in fact bad doc.