Conversion Program

import java.util.Scanner;

public class Main {


    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);

        System.out.print("Podaj odległość w metrach: ");
        double meters = input.nextDouble();

        if(meters < 0)
        {
            System.out.println("BLAD");
            System.exit(0);
        }


       do
        {
            menu();
            int choice = input.nextInt();
            switch (choice)
            {
                case 1:
                    showKilometres(meters);
                    break;

                case 2:
                    showInches(meters);
                    break;

                case 3:
                    showFeet(meters);
                    break;

                case 4:
                    System.exit(0);
                    break;

                default:
                    System.out.println("BLAD");
            }
        } while (true);

    }

    public static void showKilometres(double meters)
    {
        System.out.println("Kilometry = " + (meters * 0.001));
    }

    public static void showInches(double meters)
    {
        System.out.println("Cale = " + (meters * 39.37));
    }

    public static void showFeet(double meters)
    {
        System.out.println("Stopy = " + (meters * 3.281));
    }

    public static void menu()
    {
        System.out.println("1. Przelicz na kilometry");
        System.out.println("2. Przelicz na cale");
        System.out.println("3. Przelicz na stopy");
        System.out.println("4. Zamknij program");
    }
}