Java：将多个值返回给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，对于我正在寻找的最重要的东西，总 kg CO2 排放量，我不断得到 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，即使用以下内容打印的值： System.out.println(trans); System.out.println(elec);和 System.out.println(food);

总数应该是 25040 或其他值，具体取决于用户提供的输入值，但我不断得到总数 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办。我应该如何解决这个问题？非常感谢所有帮助！

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，一切都很好。

从这里：

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

到这里：

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

Answer 2

这里弹出的第二个问题与没有正确地将 Scanner 参数传递给多个方法有关。

我通过在 main 方法中添加以下内容来解决此问题：

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);
}

因为我有三个扫描器对象，每个方法一个，我只是删除了每个扫描器，现在可以将一个扫描器从我的主要方法传递给其他每个。