BasicLookAndFeel darcula = new DarculaLaf();
try {
  UIManager.setLookAndFeel(darcula);
} catch (UnsupportedLookAndFeelException ex) {
  Logger.getLogger(windows.class.getName()).log(Level.SEVERE, null, ex);
}

try {
  UIManager.setLookAndFeel("javax.swing.plaf.metal.MetalLookAndFeel");
} catch (UnsupportedLookAndFeelException ex) {
  Logger.getLogger(windows.class.getName()).log(Level.SEVERE, null, ex);
}
SwingUtilities.updateComponentTreeUI(frame);
frame.pack();