Distance converter

The problem

Write a program that asks the user to enter a distance in meters. The program will then present the following menu of selections:

Convert to kilometers
Convert to inches
Convert to feet
Quit the program

The program will convert the distance to kilometers, inches, or feet, depending on the user’s selection. Here are the specific requirements:

Write a method named calculateKilometers, which accepts the number of meters as an argument. The method should return the argument converted to kilometers. Convert the meters to kilometers using the following formula: kilometers = meters * 0.001
Write a method named calculateInches, which accepts the number of meters as an argument. The method should retrun the argument converted to inches, Convert the meters to inches using the following formula: inches = meters * 39.37
Write a method named calculateFeet, which accepts the number of meters as an argument. The method should return the argument converted to feet. Convert the meters to feet using the following formula:feet = meters * 3.281
Write a method named menu that returns a list of menu of selections. This method should not accept any arguments.
The program should continue to display the menu until the user enters 4 to quit the program.
If the user selects an invalid choice from the menu, the program should display an error message.

Breaking it down

Create calculateKilometers method

/**
 * The calculateKilometers method displays the kilometers that are equivalent to
 * a specified number of meters.
 *
 * @param meters
 * @return the number of kilometers
 */
static double calculateKilometers(double meters) {

    double kilometers = meters * 0.001;

    return kilometers;
}

Create calculateInches method

/**
 * This method should calculate inches that are equivalent to a specified
 * number of meters.
 *
 * @param meters
 * @return the number of inches
 */
static double calculateInches(double meters) {

    double inches = meters * 39.37;

    return inches;
}

Create calculateFeet method

/**
 * This method should calculate the feet that are equivalent to a specified
 * number of meters.
 *
 * @param meters
 * @return The number of feet.
 */
static double calculateFeet(double meters) {

    double feet = meters * 3.281;

    return feet;
}

/**
 * This method should return a collection of menu items.
 *
 * @return
 */
static List<String> getMenu() {

    List<String> menuItems = new ArrayList<String>();
    menuItems.add("Convert to kilometers");
    menuItems.add("Convert to inches");
    menuItems.add("Convert to feet");
    menuItems.add("Quit the program");

    return menuItems;
}

Create variables, scanner for keyboard input

int selection; // Menu selection
double distance; // Distance in meters

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

Ask user for input, calculate selection

// Get a distance.
System.out.print("Enter a distance in meters: ");
distance = keyboard.nextDouble();

// Display the menu and process the user's
// selection until 4 is selected.
List<String> menuItems = getMenu();
do {

    // Display the menu.
    for (int x = 0; x < menuItems.size(); x++) {
        System.out.println((x + 1) + ". " + menuItems.get(x));
    }

    // Get the user's selection.
    System.out.print("\nEnter your choice: ");
    selection = keyboard.nextInt();

    // Validate the user's selection.
    while (selection < 1 || selection > 4) {
        System.out.print("Invalid selection. Enter your choice: ");
        selection = keyboard.nextInt();
    }

    // Process the user's selection.
    switch (selection) {
        case 1:
           System.out.println(distance + " meters is " +
                   calculateKilometers(distance) + " kilometers.");
            break;
        case 2:
           System.out.println(distance + " meters is " +
                   calculateInches(distance) + " inches.");
            break;
        case 3:
           System.out.println(distance + " meters is " +
                   calculateFeet(distance) + " feet.");
            break;
        case 4:
            System.out.println("Bye!");
    }

    System.out.println();

} while (selection != 4);

Output

Enter a distance in meters: 100
1. Convert to kilometers
2. Convert to inches
3. Convert to feet
4. Quit the program

Enter your choice: 1
100.0 meters is 0.1 kilometers.

1. Convert to kilometers
2. Convert to inches
3. Convert to feet
4. Quit the program

Enter your choice: 2
100.0 meters is 3936.9999999999995 inches.

1. Convert to kilometers
2. Convert to inches
3. Convert to feet
4. Quit the program

Enter your choice: 3
100.0 meters is 328.1 feet.

1. Convert to kilometers
2. Convert to inches
3. Convert to feet
4. Quit the program

Enter your choice: 4
Bye!

Unit tests

@Test
public void test_getMenu () {

    assertNotNull(DistanceConversion.getMenu());
    assertEquals(4, DistanceConversion.getMenu().size());
}

@Test
public void test_calculateKilometers () {

    double kilometers = DistanceConversion.calculateKilometers(10000);

    assertEquals(10, kilometers, 0);
}

@Test
public void test_calculateInches () {

    double inches = DistanceConversion.calculateInches(1000);

    assertEquals(39370, inches, 0);
}

@Test
public void test_calculateFeet () {

    double feet = DistanceConversion.calculateFeet(1000);

    assertEquals(3281, feet, 0);
}

Level Up

Adjust the program so it doesn't accept negative numbers for the distance in meters.
Format numbers in output