Mutually Exclusive Radio Buttons

I am trying to create a JFrame where I have two radio buttons (choose one room or two rooms), but they need to be mutually exclusive. I know there is a lot missing from my code, but I'm trying to work through one issue at a time

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
 
public class JCottageFrame extends JFrame //implements ActionListener
{
final int ONE_ROOM = 600;
final int TWO_ROOMS = 850;
final int ROWBOAT = 60;
int price;
 
[code]....

I believe the errors are because I am trying to add the radio buttons to the button group and making them mutually exclusive, but I'm struggling to follow the textbook on how to properly do this. When I remove the two lines of code that are causing the errors, my code compiles and the JFrame shows correctly. The only issue is that it is allowing me to select "One room" and "Two rooms" at the same time.