Java：将多个值返回主要方法以计算总计

Question

代码如下。该程序根据用户输入的数据运行一系列计算。我的问题是，对于我所需要的最重要的事情，总二氧化碳排放量，我总是得到0.0的答案。我需要的是在每种方法中计算的单个总排放量的总和，即用以下值打印的值：System.out.println（trans）;的System.out.println（ELEC）;和System.out.println（食物）;

根据用户提供的输入值，总数应该是25040之类的东西，但我总是得到总数为0.0，这显然是错误的。可能与我初始化变量的方式有关，或者与从方法返回值的限制有关。我只是不知道该怎么做。我应该如何解决这个问题？所有帮助非常感谢！

import java.util.Scanner; 

public class CarbonCalc { 

    public static void main(String[] args) { 
     double trans = 0; 
     double elec = 0; 
     double food = 0; 

     giveIntro(); 

     determineTransportationEmission(null); 
     determineElecticityEmission(null); 
     determineFoodEmission(null); 

     calculateTotalEmission(trans, elec, food); 

     //printReport(trans, elec, food); 
    } 

    //Gives a brief introduction to the user. 
    public static void giveIntro() { 
     System.out.println("This program will estimate your carbon footprint"); 
     System.out.println("(in metric tons per year) by asking you"); 
     System.out.println("to input relevant household data."); 
     System.out.println(""); 
    } 

    //Determines the user's transportation-related carbon emissions. 
    public static double determineTransportationEmission(Scanner input) { 
     Scanner console = new Scanner(System.in); 
     System.out.println("We will first begin with your transportation-related carbon expenditures..."); 
     System.out.print("How many kilometres do you drive per day? "); 
     double kmPerDay = console.nextDouble(); 
     System.out.print("What is your car's fuel efficiency (in km/litre)? "); 
     double fuelEfficiency = console.nextDouble(); 
     System.out.println("We now know that the numeber of litres you use per year is..."); 
     double litresUsedPerYear = 365.00 * (kmPerDay/fuelEfficiency); 
     System.out.println(litresUsedPerYear); 
     System.out.println("...and the kg of transportation-related CO2 you emit must be..."); 

     //Final calculation of transportation-related kgCO2 emissions. 
     double trans = 2.3 * litresUsedPerYear; 
     System.out.println(trans); 
     System.out.println(""); 
     return trans; 
    } 

    //Determines the user's electricity-related carbon emissions. 
    public static double determineElecticityEmission(Scanner input) { 
     Scanner console = new Scanner(System.in); 
     System.out.println("We will now move on to your electricity-related carbon expenditures..."); 
     System.out.print("What is your monthly kilowatt usage (kWh/mo)? "); 
     double kWhPerMonth = console.nextDouble(); 
     System.out.print("How many people live in your home? "); 
     double numPeopleInHome = console.nextDouble(); 
     System.out.println("The kg of electricity-related CO2 you emit must be..."); 

     //Final calculation of electricity-related kgCO2 emissions. 
     double elec = (kWhPerMonth * 12 * 0.257)/numPeopleInHome; 
     System.out.println(elec); 
     System.out.println(""); 
     return elec; 
    } 

    //Determines the user's food-related carbon emissions. 
    public static double determineFoodEmission(Scanner input) { 
     Scanner console = new Scanner(System.in); 
     System.out.println("We will now move on to your food-related carbon expenditures..."); 
     System.out.print("In a given year, what percentage of your diet is meat? "); 
     double meat = console.nextDouble(); 
     System.out.print("In a given year, what percentage of your diet is dairy? "); 
     double dairy = console.nextDouble(); 
     System.out.print("In a given year, what percentage of your diet is fruits and veggies? "); 
     double fruitVeg = console.nextDouble(); 
     System.out.print("In a given year, what percentage of your diet is carbohydrates? "); 
     double carbs = console.nextDouble(); 

     //Final calculation of food-related kgCO2 emissions. 
     System.out.println("The kg of food-related CO2 you emit must be..."); 
     double food = (meat * 53.1 + dairy * 13.8 + fruitVeg * 7.6 + carbs * 3.1); 
     System.out.println(food); 
     System.out.println(""); 
     return food; 
    } 

    //Calculates total emissions across all sources. 
    public static double calculateTotalEmission(double trans, double elec, double food) { 
     System.out.println("Your total kg of CO2 emitted across all sources is equal to..."); 
     double total = trans + elec + food; 
     System.out.println((double) total); 
     System.out.println(""); 
     return total; 

    } 

} 

Answer 1

啊！非常感谢Lyju。我做了以下，这一切运作良好。

从这：

double trans = 0; 
double elec = 0; 
double food = 0; 

要这样：

double trans = determineTransportationEmission(null); 
double elec = determineElecticityEmission(null); 
double food = determineFoodEmission(null); 

Answer 2

其弹出这里有与不正确地传递扫描参数的多种方法做的第二个问题。

我固定，通过加入以下的主要方法：

public static void main(String[] args) { 
    Scanner console = new Scanner(System.in); 

    double trans = determineTransportationEmission(console); 
    double elec = determineElecticityEmission(console); 
    double food = determineFoodEmission(console); 

    giveIntro(); 

    calculateTotalEmission(trans, elec, food); 
} 

而且因为我有三个扫描器的物体，一个用于每个方法中，我简单地去除在每个扫描仪和现在可以通过一个单一的扫描仪从我的主要方法到其他每个方法。