java swing program converter km to miles and vice versa

I have created a program in java using swing and ActionListener the program simply to converter km to miles and vice versa. at the actionPerformed i am trying to return value to the output variable but I can not get the value back in the JTextArea.
the code attached below:

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class Converter extends JFrame implements ActionListener {
    JLabel label = new JLabel("Distance : ");
    JTextField input = new JTextField(10);
    JButton button = new JButton("Convert");
    JTextArea output = new JTextArea(10,15);
    CheckboxGroup cbg = new CheckboxGroup();
    Checkbox cb1 = new Checkbox("Convert MILES to KM", cbg, true);
    Checkbox cb2 = new Checkbox("Convert KM to MILES", cbg, false);

    public static void main(String args[]){
        Converter s = new Converter();
        s.setVisible(true);
    }

    public Converter(){
        setLayout(null);
        setSize(300,400);  
        //left-down-width-hegiht
        cb1.setBounds(60,30,150,30);
        cb2.setBounds(60,60,150,30);
        label.setBounds(30,90,120,30);
        input.setBounds(90,95,170,20);
        button.setBounds(100,130,90,30);
        output.setBounds(45,168,200,165);
                
        add(cb1);
        add(cb2);
        add(label);
        add(input);
        add(button);
        add(output);
    }

    public void actionPerformed(ActionEvent e){
        if (cb1 .equals(true) ) {
            if (e.getSource() == button ){
                double d = Double.parseDouble(input.getText());
                double d2 =  d* 0.62;
                String str2 = String.valueOf(d2); 

                output.setText(str2);
            }
            else { 
            }
        }
    }		 
}

2 things:

1. the check on the checkbox is wrong. It should be:

   if (cb1.getState()) {...}
   

2. you have to register the actionlistener in the button: in the constructor add:

   button.addActionListener(this);