I don't understand where does $64 comes from

Issue

Assume that a gallon of paint cover's about 350 square feet of wall space, ask a user to enter length, width and height. The methods should do the following:

• Calculate the wall area for a room
• Passes the calculated wall area to another method that calculates and returns the number of gallons of paint needed
• Display the number of gallons needed
• Computes the price based on a paint price $32 per gallon, assuming that the painter can buy any fraction of a gallon of paint at the same price as a whole gallon.
• returns the price to the main method. The main() method displays the final price. Example: the cost to paint a 15-by-20 room with 10-foot ceilings is $64.

Here us what I did, and I'm failing to get that $64

public static void main(String[] args){

    double  l,h,w;
    Scanner sc=new Scanner(System.in);
    System.out.print("Enter the height: ");
    h=sc.nextDouble();
    System.out.print("Enter the width: ");
    w=sc.nextDouble();
    System.out.print("Enter the length: ");
    l=sc.nextDouble();
    disGallons(calArea(h, w, l));
    disPrice(price(calGallon(calArea(h, w, l))));
}

public static double calArea(double h,double w, double l){
    double area=2*((w*h)+(l*w)+(l*h));
    return area;
}
public static double calGallon(double area){
    double gallons= area/350;
    return gallons;
}
public static void disGallons(double gallons){
    System.out.println("Gallons needed: "+gallons);
}
public static double price(double gallon){
    final double gallPrice=32;
    return (int)(gallPrice*gallon);
}
public static void disPrice(double price){
    System.out.println("Total Price is: $"+price);
}

Solution

Here's how I'd do it.

package io.duffymo;

/**
 * Size the amount of paint needed
 * @link <a href="https://stackoverflow.com/questions/72404779/i-dont-understand-where-does-64-comes-from">...</a>
 */
public class PaintSizing {

    public static final double PRICE_PER_GALLON_USD = 32.0;
    public static final double SQ_FEET_PER_GALLON = 350.0;

    public static double area(double h, double w, double l) {
        return 2.0*(w + l)*h;
    }

    public static double gallons(double area) {
        return area / SQ_FEET_PER_GALLON;
    }

    public static double price(double gallons) {
        return gallons * PRICE_PER_GALLON_USD;
    }
}

It's never too soon to learn about JUnit:

package io.duffymo;

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

public class PaintSizingTest {

    @Test
    public void testSizing() {
        // setup
        double l = 15.0;
        double w = 20.0;
        double h = 10.0;
        double expectedArea = 700.0;
        double expectedGallons = 2.0;
        double expectedPrice = 64.0;
        // exercise
        double actualArea = PaintSizing.area(h, w, l);
        double actualGallons = PaintSizing.gallons(actualArea);
        double actualPrice = PaintSizing.price(actualGallons);
        // assert
        Assertions.assertEquals(expectedArea, actualArea, 0.001);
        Assertions.assertEquals(expectedGallons, actualGallons, 0.001);
        Assertions.assertEquals(expectedPrice, actualPrice, 0.001);
    }

}

Answered By - duffymo