code: public void setTargetWidth (int targetWidth)
      {
          if (targetWidth <= 0) {
              throw new IllegalArgumentException(
                  "Invalid target width '" + targetWidth + "'");
          }
          _constraints.width = targetWidth;
          _constraints.height = 0;
          invalidate("setTargetWidth");
      }
docs: Sets the target width for this label. Text will be wrapped to fit into this width, forcibly
  breaking words on character boundaries if a single word is too long to fit into the target
  width. Calling this method will annul any previously established target height as we must
  have one degree of freedom in which to maneuver.
  
  <p> This should be followed by a call to {@link #layout} before a call is made to {@link
  #render} as this method invalidates the layout information.