How can I calculate BMI in Java Where the weight and height is an array

Question

I have an assignment in Java, where I have to calculate the BMI of a particular user, in an array of users, an array of heights and an array of weights.

Below is the assignment:

  String[] names; // users names
                String[] familyNames; // familyNames
                int[] weight; // users weights in kilograms (kg)
                double[] height; // users height in meter (m)


                names = new String[] { "Alex", "Maria", "Anna", "Adam", "Sara", "Johan", "Frederik"};
                familyNames = new String[] {"Andersson", "Johansson", "Nordin", "Holmgren", "Svensson"};
                weight = new int[] {70, 50, 60, 50, 60, 87, 130 };
                height = new double[] { 1.80, 1.70, 1.57, 1.80, 1.69, 1.85, 1.85 };

        public static void calculateBMI(String name, String[] names, int[] weight, double[] height) {


                /*
                 * This method should be changed
                 * 
                 * Calculate and print out BMI (body mass index) for each user 
                 * BMI = weight in kg/height in meter * height in meter 
                 * 
                 * Check if the user is Underweight, Normal, Overweightor or Obese based on the BMI
                 * Underweight, when bmi is less than 18.5 
                 * Normal, when bmi is between 18.5 and 24.9 
                 * Overweight, when bmi is between 25 and 29.9
                 * Obese, when bmi is more than 30
                 * 
                 * 
                 * To check if a string is equal to another string use:
                 * stringVariable.equalsIgnoreCase(anotherStringVariable)
                 * 
                 */

            }

public static void calculateWeight(String name, String[] names, int[] weight, double[] height) {

        /*
         * This method should be changed
         * 
         * Calculate and print out the weight that the user has to loose or gain
         * 
         * Let's consider that the formula for ideal body weight is (Broca Index:):
         * Ideal Body Weight (kg) = (Height (cm) - 100) - ((Height (cm) - 100) x 10%)
         * 
         * 1 meter = 100 cm
         * 
         * 
         */
        //Your code starts here


    }// end calculateWeightLoss

I have tried doing this:

double userBMI = 0;
   for(int i = 0; i < weight.length; i++){
                for(int j = 0; j < height.length; j++){
                    userBMI = weight[i]/height[j] * height[j];
                }
            }

But I feel I am not on track, because the method when in use will be:

calculateBMI("Frederik",names, weight,height); // calculate user BMI
        calculateWeight("Frederik", names, weight, height); // calculate the weight loss or gain for the user
        System.out.println("");

So I have to find for example "frederik" in the array of names, and calculate his BMI. Any ideas will be aappreciated.

First of all userBMI = weight[i]/height[j] * height[j]; is not a correct way to calculate BMI — Rafał Sokalski, Nov 07 '18 at 07:48
What exactly should do method calculateBMI because it says that it should calculate BMI for each user but you pass name to this method ? — Rafał Sokalski, Nov 07 '18 at 07:54
You should study [Classes and Objects](https://docs.oracle.com/javase/tutorial/java/javaOO/index.html) from the Java Lessons. You should not put all these data into a bunch of arrays, but use a class like `Person` instead. See [László Stahorszki's answer](https://stackoverflow.com/a/53185522/507738). It looks like the `calculateWeight` method is defined by the assignment, but it's bad design. — MC Emperor, Nov 07 '18 at 08:35

Rafał Sokalski · Accepted Answer · 2018-11-07T08:38:09.367

It print the BMI when passed to the method name match with the name in "names" array

public static void calculateBMI(String name, String[] names, int[] weight, double[] height) {

    for (int i = 0; i < names.length; i++) {
        if(names[i].equalsIgnoreCase(name))
            System.out.println(weight[i] / height[i] / height[i]);
    }
}

But it is risky because if the length of names array is bigger than weight or height it will throw ArrayIndexOutOfBoundsException but I assume that arrays have always properly length. If there is possibility that the length of these arrays might be different I suggest to add some conditions

And the second method:

public static void calculateWeight(String name, String[] names, int[] weight, double[] height) {

    for (int i = 0; i < names.length; i++) {
        if (names[i].equalsIgnoreCase(name)) {
            double perfectWeight = ((height[i] * 100) - 100) - (((height[i] * 100) - 100) / 10);
            System.out.println("Perfect weight for that height is : " + perfectWeight);
            if(weight[i] == perfectWeight)
                System.out.println("Person has perfect weight");
            else if(weight[i] > perfectWeight)
                System.out.println("Person should lose: " + (weight[i] - perfectWeight));
            else
                System.out.println("Person should gain: " + (perfectWeight - weight[i]));
        }

    }
}

First it calculate the perfect weight and then it is compared to Person weight and print if the person should lose or gain some kg

score 0 · Answer 2 · answered Nov 07 '18 at 08:05

I'd suggest you to write a class, let's call it Person. In each instance of this class, you can store the name, the height and weight of a given person.

class Person {
    private String name;
    private String familyName;
    private int weight;
    private double height;
}

In this class, it's really simple, to write a method which returns the BMI. To create these instances, you can use a method similar to the answer above, however, I'd recommend you do addiditonal checks, whether the arrays are of the same size.

MC Emperor · Answer 3 · 2018-11-07T09:10:04.103

First, I'm not going to write that code for you, I think you should eventually do it on your own.

Here are some hints:

The assignment is not quite accurate. It says "calculate and print out BMI (body mass index) for each user", but then it requires you to implement a method accepting a specific name as the first argument. The fact that the description mentions the equalsIgnoreCase method, suggests that you need to display the BMI only of that given user.
So you need a sort of loop, perhaps a for loop. Within the loop, check if the name is correct. You don't need a nested loop, why do you want to use a nested loop?
You may assert that all given arrays are equal of length, since the assignment does not mention array lengths. You might want to re-check the length of familyNames, since it's shorter than the other arrays.

You might want to create a new method which does the actual BMI calculation, and refer to it from the calculateBMI method:

private static double calculateActualBmi(int weigth, double height) {
    return ...; // perform calculation
}

And separate the actual calculation from describing the BMI.

private static String describeBmi(double bmi) {
    if (bmi < 18.5) {
        return "Underweight";
    }
    else if ...
        ...
    else {
        return "Obese";
    }
}

The other method kind of works the same way.

Further notes

I'm surprised that the assignment requires you to write the method calculateBMI(String name, String[] names, int[] weight, double[] height) like this. This design misses the whole point of object-oriented programming. See László Stahorszki's answer.

You could declare and initialize the arrays at once, i.e.

String[] names = new String[] { "Alex", ..., "Frederik" };

How can I calculate BMI in Java Where the weight and height is an array

3 Answers3