If you want to select  one of your JRadioButton you need toadd them in one group.ButtonGroup class will do it for you. Look at the sample:
public class RadioButtonDemo{
JFrame f = new JFrame();
Container c = f.getContentPane();
c.setLayout();
//Instances RaidioButtons
JRadioButton btn1 = new JRadioButon();
JRadioButton btn2 = new JRadioButon();
JRadioButton btn3 = new JRadioButon();

ButtonGroup group = new ButtonGroup();
group.add(btn1);
group.add(btn2);
group.add(btn3);

c. add(btn1);
c. add(btn2);
c. add(btn3);

f.pack();
f.setVisible(true);


}