问如何在屏幕上居中显示JDialog？

EN

final JDialog d = new JDialog();
d.setSize(200,200);
d.setLocationRelativeTo(null);
d.setVisible(true);

final JDialog d = new JDialog();
d.setSize(200, 200);
final Toolkit toolkit = Toolkit.getDefaultToolkit();
final Dimension screenSize = toolkit.getScreenSize();
final int x = (screenSize.width - d.getWidth()) / 2;
final int y = (screenSize.height - d.getHeight()) / 2;
d.setLocation(x, y);
d.setVisible(true);

setLocation((Toolkit.getDefaultToolkit().getScreenSize().width)/2 - getWidth()/2, (Toolkit.getDefaultToolkit().getScreenSize().height)/2 - getHeight()/2);

// Center on screen ( absolute true/false (exact center or 25% upper left) )
public void centerOnScreen(final Component c, final boolean absolute) {
    final int width = c.getWidth();
    final int height = c.getHeight();
    final Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
    int x = (screenSize.width / 2) - (width / 2);
    int y = (screenSize.height / 2) - (height / 2);
    if (!absolute) {
        x /= 2;
        y /= 2;
    }
    c.setLocation(x, y);
}

// Center on parent ( absolute true/false (exact center or 25% upper left) )
public void centerOnParent(final Window child, final boolean absolute) {
    child.pack();
    boolean useChildsOwner = child.getOwner() != null ? ((child.getOwner() instanceof JFrame) || (child.getOwner() instanceof JDialog)) : false;
    final Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
    final Dimension parentSize = useChildsOwner ? child.getOwner().getSize() : screenSize ;
    final Point parentLocationOnScreen = useChildsOwner ? child.getOwner().getLocationOnScreen() : new Point(0,0) ;
    final Dimension childSize = child.getSize();
    childSize.width = Math.min(childSize.width, screenSize.width);
    childSize.height = Math.min(childSize.height, screenSize.height);
    child.setSize(childSize);        
    int x;
    int y;
    if ((child.getOwner() != null) && child.getOwner().isShowing()) {
        x = (parentSize.width - childSize.width) / 2;
        y = (parentSize.height - childSize.height) / 2;
        x += parentLocationOnScreen.x;
        y += parentLocationOnScreen.y;
    } else {
        x = (screenSize.width - childSize.width) / 2;
        y = (screenSize.height - childSize.height) / 2;
    }
    if (!absolute) {
        x /= 2;
        y /= 2;
    }
    child.setLocation(x, y);
}