I need input from my main module into another module created after

Question

Java "Fat Gram Calculator" programming I'm attempting needs to validate input, I get to a point where I need to validate the input from user, taking into consideration a previous input from another module, with a given formula. I am trying this and I don't know how to do that without asking the user to input the same thing again, please help the problem is on this line:

while(input < 0.0 || input < (fatGrams * 9)){

in the code below

import java.util.Scanner;
class fatCalculator {

    public static void main(String[] args) {
        // Local variables
        double fatGrams, calories;

        // Calls getFat
        fatGrams = getFat();
        // Calls getCalories
        calories = getCalories();
        // Calls showPercent
        showPercent(fatGrams, calories);
    }
    public static double getFat() {
        Scanner keyboard = new Scanner(System.in);

        // Local variable
        double input;

        // Get the fat grams  
        System.out.println("Please enter the number of fat grams: ");
        input = keyboard.nextDouble();

        // Valitdate
        while (input < 0.0) {
            System.out.println("The number of fat grams cannot be less than 0.");
            System.out.println("Please enter the number of fat grams.");
            input = keyboard.nextDouble();
        }
        return input;
    }
    public static double getCalories() {
        Scanner keyboard = new Scanner(System.in);

        // Local variable
        double input;
        // call fatGrams


        // Get the calories
        System.out.println("Please enter the number of calories: ");
        input = keyboard.nextDouble();

        // Validate
        while (input < 0.0 || input < (fatGrams * 9)) { // <<<<<< PROBLEM IS HERE
            System.out.println("The number of calories cannot be less than the number of fat grams * 9.");
            System.out.println("Please enter the number of calories.");
            input = keyboard.nextDouble();
        }
        return input;
    }
    public static void showPercent(double fatGrams, double calories) {
        // local varibale
        double finalPercentage;

        // Calculate and display final percentage
        finalPercentage = (fatGrams * 9) / calories;
        System.out.println("The percentage of calories from fat is " + finalPercentage);
        // Banner
        while (finalPercentage < 0.3) {
            System.out.println("That food item is considered" + "low fat.");
        }
    }
}

Answer 1

You need to pass the fatGrams variable as an argument to the getCalories() method, like this:

    // Calls getFat
    fatGrams = getFat();
    // Calls getCalories
    calories = getCalories(fatGrams);
    // Calls showPercent
    showPercent(fatGrams, calories);
}

And change the signature of your getCalories() method like this:

public static double getCalories(double fatGrams) {
    Scanner keyboard = new Scanner(System.in);

Now the class can compile and the following line doesn't have any problem anymore:

    // Validate
    while (input < 0.0 || input < (fatGrams * 9)) { // <<<<<< NO MORE PROBLEM !

Hope it helps.