JRadioButton: Simpler Example

import javax.swing.*;
import java.awt.*;
import java.awt.event.*; // step 1

// Mututally exclusive == >ButtonGroup

public class JRadioButtonDemo extends JFrame //step 2
                             implements ActionListener{

  private JRadioButton rbtn1 = new JRadioButton("Ivan");
  private JRadioButton rbtn2 = new JRadioButton("Kwan Yong");
  private JButton btn = new JButton("Vote");
  
  private ButtonGroup btngrp = new ButtonGroup();

  public JRadioButtonDemo() {

    btngrp.add(rbtn1); // For making one radiobutton clickable at one time
    btngrp.add(rbtn2);
    
    rbtn1.setSelected(true); // Set Ivan to be default
    
    getContentPane().setLayout(new FlowLayout());
    getContentPane().add(rbtn1);
    getContentPane().add(rbtn2);
    getContentPane().add(btn);

    btn.addActionListener(this);//step 4:

  } //end constructor

  public void actionPerformed(ActionEvent ev){//step 3

    String name = "";
    if (ev.getSource() == btn){
      if (rbtn1.isSelected()){ // Ivan was voted
        name = "Ivan";
      }
      else if (rbtn2.isSelected()){
        name = "Kwan Yong";
      }
      
      JOptionPane.showMessageDialog(null, "You voted for " + name);
    }//end if

  } //end actionPerformed

  public static void main(String[] args) {
    JRadioButtonDemo f = new JRadioButtonDemo();
    f.setTitle("OOPG");
    f.setSize(300, 300);
    f.setVisible(true);

  } //end main
} //end class