Speed of sound

The problem

The following table shows the approximate speed of sound in air, water, and steel.

Medium Speed

Air 1,100 feet per second
Water 4,900 feet per second
Steel 16,400 feet per second

Write a program that displays a menu allowing the user to select air, water, or steel. After the user has made a selection, he or she should ask to enter the distance a sound wave will travel in the selected medium. The program will then display the amount of time it will take (round the answer to 4 decimal places). Input validation: check that the user has selected one of the available choices from the menu.Do not accept distances less than 0.

Breaking it down

Create variables

double distance = 0.0; // Distance
String medium; // To hold "air", "water", or "steel"

// Create a Scanner object for keyboard input.
Scanner keyboard = new Scanner(System.in);

Create distance travelled method

/**
 * Method should return the distance traveled in seconds.
 *
 * @param medium
 * @param distance
 * @throws NullPointerException when medium is null
 *
 * @return distance traveled
 */
static double getDistanceTraveledInSeconds(String medium, double distance) {

    checkNotNull(medium);

    if (medium.equalsIgnoreCase("air")) {
        return distance / 1100.0;
    } else {
        if (medium.equalsIgnoreCase("water")) {
            return distance / 4900.0;
        } else {
            if (medium.equalsIgnoreCase("steel")) {
                return distance / 16400.0;
            }
        }
    }
    return 0.0;
}

Get input from user

// Get the user's medium of choice.
System.out.print("Enter one of the following: air, water, or steel: ");
medium = keyboard.nextLine();

// Get the distance.
System.out.print("Enter the distance the sound wave will travel: ");
distance = keyboard.nextDouble();

Calculate and display output

// calculate 
double distanceTravelled = getDistanceTraveledInSeconds(medium, distance);

// display output
System.out.println("It will take " + distanceTravelled + " seconds.");

Output

Enter one of the following: air, water, or steel: air
Enter the distance the sound wave will travel: 4500
It will take 4.090909090909091 seconds.

Unit tests

@Test(expected=NullPointerException.class)
public void get_distance_travelled_in_seconds_null_medium () {
    SpeedOfSound.getDistanceTraveledInSeconds(null, 333);
}

@Test
public void get_distance_travelled_in_seconds_air () {
    double val = SpeedOfSound.getDistanceTraveledInSeconds("air", 1100);
    assertEquals(1, val, 0);
}

@Test
public void get_distance_travelled_in_seconds_water () {
    double val = SpeedOfSound.getDistanceTraveledInSeconds("water", 4900);
    assertEquals(1, val, 0);
}

@Test
public void get_distance_travelled_in_seconds_steel () {
    double val = SpeedOfSound.getDistanceTraveledInSeconds("steel", 16400);
    assertEquals(1, val, 0);
}


@Test
public void get_distance_travelled_in_seconds_nothing () {
    double val = SpeedOfSound.getDistanceTraveledInSeconds("", 16400);
    assertEquals(0, val, 0);
}

Level Up

Validate the users inputs for air/water/steel
Create ENUM OR constants for air/water/steel, be sure to update the test!
Allow the user to enter have the ability to show the feet per second in time. adjust the getDistanceTraveledInSeconds -> getDistancedTraveled