Radio Button

public class MyForm extends JFrame {

    public MyForm() {

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        setBounds(100, 100, 343, 273);

        setTitle("Kittisay Java");

        setLayout(null);

        // Radio Button

        JRadioButton radio1 = new JRadioButton("Item 1");

        radio1.setBounds(119, 58, 109, 23);

        add(radio1);

        JRadioButton radio2 = new JRadioButton("Item 2");

        radio2.setBounds(119, 84, 109, 23);

        add(radio2);

        JRadioButton radio3 = new JRadioButton("Item 3");

        radio3.setBounds(119, 110, 109, 23);

        add(radio3);

        // Set Group

        ButtonGroup group = new ButtonGroup();

        group.add(radio1);

        group.add(radio2);

        group.add(radio3);

        // Button

        JButton btn = new JButton("Button");

        btn.addActionListener((e) -> {

            if (radio1.isSelected()) {

                JOptionPane.showMessageDialog(null, "You select : Item 1");

            } else if (radio2.isSelected()) {

                JOptionPane.showMessageDialog(null, "You select : Item 2");

            } else if (radio3.isSelected()) {

                JOptionPane.showMessageDialog(null, "You select : Item3");

            } else {

                JOptionPane.showMessageDialog(null, "You not select.");

            }

        });

        btn.setBounds(125, 154, 89, 23);

        add(btn);   

    }

    public static void main(String[] args) {

      MyForm frm = new MyForm();

      frm.setVisible(true);

    }