addNonNull(c);
addNonNull(c, JScrollPane.LOWER_RIGHT_CORNER);
  public void setCorner(String key, Component c)  {    if (getComponentOrientation()         == ComponentOrientation.LEFT_TO_RIGHT)      {        if (key == LOWER_LEADING_CORNER)          key = LOWER_LEFT_CORNER;        else if (key == LOWER_TRAILING_CORNER)          key = LOWER_RIGHT_CORNER;        else if (key == UPPER_LEADING_CORNER)          key = UPPER_LEFT_CORNER;        else if (key == UPPER_TRAILING_CORNER)          key = UPPER_RIGHT_CORNER;      }    else if (getComponentOrientation()              == ComponentOrientation.RIGHT_TO_LEFT)      {        if (key == LOWER_LEADING_CORNER)          key = LOWER_RIGHT_CORNER;        else if (key == LOWER_TRAILING_CORNER)          key = LOWER_LEFT_CORNER;        else if (key == UPPER_LEADING_CORNER)          key = UPPER_RIGHT_CORNER;        else if (key == UPPER_TRAILING_CORNER)          key = UPPER_LEFT_CORNER;      }    if (key == LOWER_RIGHT_CORNER)      {        removeNonNull(lowerRight);        lowerRight = c;        addNonNull(c);      }    else if (key == UPPER_RIGHT_CORNER)      {        removeNonNull(upperRight);        upperRight = c;        addNonNull(c);      }    else if (key == LOWER_LEFT_CORNER)      {        removeNonNull(lowerLeft);        lowerLeft = c;        addNonNull(c);      }    else if (key == UPPER_LEFT_CORNER)      {        removeNonNull(upperLeft);        upperLeft = c;        addNonNull(c);      }    else      throw new IllegalArgumentException("unknown corner " + key);    sync();  }