Java: Dialog I/O: Kilometers to Miles

// intro-dialog/KmToMiles.java - Convert kilometers to miles.
// Use JOptionPane for input / output.
// Michael Maus, 28 Oct 2004

import javax.swing.*;

public class KmToMiles {
    
    //================================================================= main
    public static void main(String[] args) {
        //... Local variables
        String kmStr;    // String km before conversion to double.
        double km;       // Number of kilometers.
        double mi;       // Number of miles.
        
        //... Input
        kmStr = JOptionPane.showInputDialog(null, "Enter kilometers.");
        km = Double.parseDouble(kmStr);
        
        //... Computation
        mi = km * 0.621;  // There are 0.621 miles in a kilometer.
        
        //... Output
        JOptionPane.showMessageDialog(null, km + " kilometers is " 
                                          + mi + " miles.");
        
        //... Stop
        System.exit(0);  // Stop GUI program
    }
}