NaN output in Java OOP

Bella Swan

I just started learning Java and I'm trying to create a simple BMI calculator using the OOP concept.

Here are my codes:

import java.util.Scanner;

class BIM 
{
    int weight;
    double weightKG = weight * 0.45359237;
    int height;
    double heightMETERS = height * 0.0254;
    double BMI = weightKG / (heightMETERS * heightMETERS);
    public void calculateBMI()
    {    
        System.out.print("The BMI is: " + BMI);
    }
}

public class BMI 
{
    public static void main(String args[] ) throws Exception 
    {
        Scanner input = new Scanner(System.in);
        
        System.out.print("Enter weight in pounds: ");
        int weight = input.nextInt();
        
        System.out.print("Enter height in inches: ");
        int height = input.nextInt();
        
        BIM b = new BIM();
        b.calculateBMI(); 
    }
    
    private static void bmiCategory (double BMI)
    {
    
        if (BMI < 18.5)
        {
            System.out.println("Underweight");
        }
        else if (BMI < 25.0)
        {
            System.out.println("Normal");
        }
        else if (BMI < 30.0)
        {
            System.out.println("Overweight");
        }
        else
        {
            System.out.println("Obese");
        }            
    }
}

The output of my codes:

Enter weight in pounds: 100 Enter height in inches: 50 The BMI is: NaN

Why am I getting the output NaN? and also, why is not displaying the category?

Elliott Frisch

Your BIM class does all the math, but you never pass a height or weight to it (and you do the math before you assign those values anywhere). First, fix BIM. Something like,

class BIM {
    public BIM(int weight, int height) {
        this.weight = weight;
        this.height = height;
        this.weightKG = weight * 0.45359237;
        this.heightMETERS = height * 0.0254;
        this.BMI = weightKG / (heightMETERS * heightMETERS);
    }

    int weight;
    double weightKG;
    int height;
    double heightMETERS;
    double BMI;

    public void calculateBMI() {
        System.out.print("The BMI is: " + BMI);
    }
}

Then instead of