Thread: Problem Calculating emmisions

I get NaN for all the values when I run the code. Not sure why? Here is the code.

import java.util.ArrayList;
class CO2FromElectricity
 
{
   CO2FromElectricity()
   {
   	//default constructor to be used
   }
 
   public double calcAverageBill(ArrayList<Double> monthlyBill)
   {
       // **** insert code for method here ****//
       monthlyBill = new ArrayList<Double>();
       double aveBill = 0;
       double bIS = 0;
       for(int i = 0; i < monthlyBill.size(); i++)
       bIS += monthlyBill.get(i);
       aveBill = bIS / monthlyBill.size();
       return aveBill;
   }
 
   public double calcAveragePrice (ArrayList<Double> monthlyPrice)
   {
        // **** insert code for method here ****//
        monthlyPrice = new ArrayList<Double>();
       double avePrice = 0;
       double pS = 0;
       for(int i = 0; i < monthlyPrice.size(); i++)
       pS += monthlyPrice.get(i);
       avePrice = pS / monthlyPrice.size();
       return avePrice;
   }
 
   public double calcElectricityCO2 (double avgBill, double avgPrice)
   {
        // **** insert code for method here ****//
         double emmisions = ((avgBill / avgPrice)*1.37*12);
         return emmisions;
   }
}

And for the tester.

import java.util.ArrayList;
public class CO2FromElectricityTester
{
   public static void main(String[] args)
   {
       	CO2FromElectricity CO2 = new CO2FromElectricity();
 
       	ArrayList<Double> monthlyBill = new ArrayList<Double>();
       	ArrayList<Double> monthlyPrice = new ArrayList<Double>();
 
       	//Values to add to the monthly bill or use your own:
       	monthlyBill.add(209.60);
        monthlyBill.add(249.68); 
        monthlyBill.add(222.59);
        monthlyBill.add(209.60);
        monthlyBill.add(249.68); 
        monthlyBill.add(222.59);
        monthlyBill.add(209.60);
        monthlyBill.add(249.68); 
        monthlyBill.add(222.59);
        monthlyBill.add(209.60);
        monthlyBill.add(249.68); 
        monthlyBill.add(222.59);
 
       	// Values to add to the monthly Price or use your own:
		// 
 
		monthlyPrice.add(209.70 / 2464);
		monthlyPrice.add(249.68 / 2948);
		monthlyPrice.add(222.59 / 2621);
		monthlyPrice.add(209.70 / 2464);
		monthlyPrice.add(249.68 / 2948);
		monthlyPrice.add(222.59 / 2621);
		monthlyPrice.add(209.70 / 2464);
		monthlyPrice.add(249.68 / 2948);
		monthlyPrice.add(222.59 / 2621);
		monthlyPrice.add(209.70 / 2464);
		monthlyPrice.add(249.68 / 2948);
		monthlyPrice.add(222.59 / 2621);
 
       double avgBill = CO2.calcAverageBill(monthlyBill);
       double avgPrice = CO2.calcAveragePrice(monthlyPrice);
 
       double emissions = CO2.calcElectricityCO2(avgBill, avgPrice);
 
       System.out.printf("Average Monthly Electricity Bill: %6.2f%n", avgBill);
       System.out.printf("Average Monthly Electricity Price: %4.2f%n", avgPrice);
       System.out.printf("Annual CO2 Emissions from Electricity Usage:   %7.1f pounds", emissions);
   }
}

You're not using the values passed to the CO2 methods, but creating empty/null values to use instead:

   public double calcAverageBill(ArrayList<Double> monthlyBill)
   {
       // **** insert code for method here ****//
       monthlyBill = new ArrayList<Double>();
       double aveBill = 0;
       double bIS = 0;
       for(int i = 0; i < monthlyBill.size(); i++)
       bIS += monthlyBill.get(i);
       aveBill = bIS / monthlyBill.size();
       return aveBill;
   }

If you delete or comment out the line,

monthlyBill = new ArrayList<Double>();

all should be well. Do you understand why? If not, please ask.

Wait why?
Also should I do the same thing for Monthly Price.

I realized it worked but don't understand why the value would be null.

--- Update ---

Oh now I see it's because its already initialized in param, so when you reinitialize in the subcode itself it is null, I suppose , because Java is sequential, it takes the null value. Thanks.

Maybe you get it, but I can't tell from your choice of words. I'm not sure about the sequential part.

I would say it differently: The values passed from the main() method to the CO2FromElectricity methods in the argument variables were replaced by new local variables of the same name (that's why they are replaced) that are initialized empty/null.