How to use

javax.swing.plaf.nimbus.NimbusLookAndFeel

constructor

  private static void openMainForm(String title, Parameters parameters) {
    try {
      UIManager.setLookAndFeel(new NimbusLookAndFeel());
    } catch (UnsupportedLookAndFeelException e) {
      throw new RuntimeException(e);
    }

    MainFrame form = new MainFrame(title, parameters);
    form.pack();
    form.setLocationRelativeTo(null);
    form.setVisible(true);
  }
}

  UIManager.setLookAndFeel(new javax.swing.plaf.nimbus.NimbusLookAndFeel());
} catch (UnsupportedLookAndFeelException e) {

  UIManager.setLookAndFeel(new NimbusLookAndFeel());
} catch (UnsupportedLookAndFeelException e) {
  e.printStackTrace();

  UIManager.setLookAndFeel(new NimbusLookAndFeel());
} catch (UnsupportedLookAndFeelException e) {
  e.printStackTrace();