SpeedConverter.java

public class SpeedConverter {

    /*
    Speed Converter

    1. Write a method called toMilesPerHour that has 1 parameter of type double
    with the name kilometersPerHour. This method needs to return the rounded value
    of the calculation of type long.
    If the parameter kilometersPerHour is less than 0,
    the method toMilesPerHour needs to return -1 to indicate an invalid value.
    Otherwise, if it is positive, calculate the value of miles per hour,
    round it and return it. For conversion and rounding,
    check the notes in the text below.

    Examples of input/output:
    toMilesPerHour(1.5); → should return value 1
    toMilesPerHour(10.25); → should return value 6
    toMilesPerHour(-5.6); → should return value -1
    toMilesPerHour(25.42); → should return value 16
    toMilesPerHour(75.114); → should return value 47

    2. Write another method called printConversion with 1 parameter of type double with the name kilometersPerHour.
    This method should not return anything (void) and it needs to calculate milesPerHour from the kilometersPerHour parameter.
    Then it needs to print a message in the format "XX km/h = YY mi/h".
    XX represents the original value kilometersPerHour.
    YY represents the rounded milesPerHour from the kilometersPerHour parameter.
    If the parameter kilometersPerHour is < 0 then print the text "Invalid Value".

    Examples of input/output:
    printConversion(1.5); → should print the following text
    (into the console - System.out): 1.5 km/h = 1 mi/h
    printConversion(10.25); → should print the following text
    (into the console - System.out): 10.25 km/h = 6 mi/h
    printConversion(-5.6); → should print the following text
    (into the console - System.out): Invalid Value
    printConversion(25.42); → should print the following text
    (into the console - System.out): 25.42 km/h = 16 mi/h
    printConversion(75.114); → should print the following text
    (into the console - System.out): 75.114 km/h = 47 mi/h

    Use method Math.round to round the number of calculated miles per hour(double).
    The method round returns long.

    TIP: In the method printConversion, call the method toMilesPerHour instead of duplicating the code.
    NOTE: All methods should be defined as public static like we have been doing so far in the course.
    NOTE: 1 mile per hour is 1.609 kilometers per hour.
     */

    public static void main(String[] args) {
        System.out.println(toMilesPerHour(1.5));
        System.out.println(toMilesPerHour(10.25));
        System.out.println(toMilesPerHour(-5.6));
        System.out.println(toMilesPerHour(25.42));
        System.out.println(toMilesPerHour(75.114));

        System.out.println("");

        printConversion(1.5);
        printConversion(10.25);
        printConversion(-5.6);
        printConversion(25.42);
        printConversion(75.114);
    }

    public static double toMilesPerHour(double kilometerPerHour) {
        if (kilometerPerHour < 0) {
            return -1;
        } else {
            //Calculate the value of miles per hour.
            //1 mile per hour is 1.609 kilometers per hour.
            double convertedNumber = kilometerPerHour / 1.609;
            //Rounding the value.
            double roundedConvertedNumber = Math.round(convertedNumber);
            //Returning the value.
            return roundedConvertedNumber;
        }
    }

    public static void printConversion(double kilometersPerHour){
        if (kilometersPerHour < 0){
            System.out.println("Invalid Value");
        }
        //km/h = how many mi/h?
        double kilometersToMPH = kilometersPerHour * .621;
        double roundedKilometersToMPH = Math.round(kilometersToMPH);
        //Printing the result.
        System.out.println(kilometersPerHour + " km/h = " + roundedKilometersToMPH + " mi/h");
    }
}