Navigation/selection with keyboard of each JRadioButton in a ButtonGroup is not possible when a Synth based Look and Feel like Nimbus is used. The test below demonstrates the issue- the issue was introduced with Java 9. The relevant code is in located in BasicRadioButtonUI - it looks like KeyHandler and actions haven't been ported to SynthRadioButtonUI for some reason.


public class RadioButtonGroupTest extends JFrame
{
  public RadioButtonGroupTest()
  {
    setName(getClass().getSimpleName());
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setLayout(new FlowLayout());

    final JRadioButton one = new JRadioButton("one");
    final JRadioButton two = new JRadioButton("two");
    final JRadioButton three = new JRadioButton("three");
    add(one);
    add(two);
    add(three);
    add(new JButton("hello"));

    final ButtonGroup grp = new ButtonGroup();
    grp.add(one);
    grp.add(two);
    grp.add(three);
    setSize(300, 400);
    setLocationRelativeTo(null);
    setVisible(true);
  }
  
  public static void main(final String[] args) throws Exception
  { UIManager.setLookAndFeel("javax.swing.plaf.nimbus.NimbusLookAndFeel");
    SwingUtilities.invokeLater(() -> new RadioButtonGroupTest());
  }
}