Java Arraylist程序

我做了一个程序，但输出显示

0

。你能看出我做错了什么吗？ 我的评估说明要求这样做

package snippet;

import java.util.ArrayList;

public class CO2FromElectricity {
    // declaration of private instance variables

    /**
     * Default constructor to create an object from the CO2FromElectricity class.
     */
    CO2FromElectricity() {
    }

    /**
     * A mutator method which calculates the average annual electricity bill.
     * 
     * @param monthlyBill
     *            an ArrayList containing the monthly bills for home electricity use.
     * @return the average monthly electricity bill.
     */
    public double calcAverageBill(ArrayList<Double> monthlyBill) {
        monthlyBill.add(279.41);
        monthlyBill.add(238.03);
        monthlyBill.add(248.64);
        monthlyBill.add(258.73);
        monthlyBill.add(395.48);
        monthlyBill.add(419.91);
        monthlyBill.add(431.15);
        monthlyBill.add(407.56);
        monthlyBill.add(417.14);
        monthlyBill.add(308.35);
        monthlyBill.add(337.91);
        monthlyBill.add(320.77);
        double sum = 0.0;
        double monthlyTotal = 0.0;

        for (int i = 0; i < monthlyBill.size(); i++) {
            sum += monthlyBill.get(i);
        }

        return monthlyTotal / monthlyBill.size();
    }

    /**
     * A mutator method which calculates the average annual price of electricity.
     * 
     * @param monthlyPrice
     *            an ArrayList containing the monthly price of electricity per kilowatthour.
     * @return the average monthly price of electricity.
     */
    public double calcAveragePrice(ArrayList<Double> monthlyPrice) {
        monthlyPrice.add(0.1117);
        monthlyPrice.add(0.1107);
        monthlyPrice.add(0.1110);
        monthlyPrice.add(0.1113);
        monthlyPrice.add(0.1135);
        monthlyPrice.add(0.1138);
        monthlyPrice.add(0.1217);
        monthlyPrice.add(0.1215);
        monthlyPrice.add(0.1216);
        monthlyPrice.add(0.1228);
        monthlyPrice.add(0.1209);
        monthlyPrice.add(0.1192);
        double sum = 0.0;
        double monthlyTotal = 0.0;

        for (int i = 0; i < monthlyPrice.size(); i++) {
            sum += monthlyPrice.get(i);
        }
        return monthlyTotal / monthlyPrice.size();
    }

    /**
     * A mutator method which calculates the annual home CO2 emission from electricity.
     * 
     * @param avgBill
     *            the average monthly home electricity bill.
     * @param avgPrice
     *            the average monthly price of home electricity.
     * @return the annual home CO2 emission from home electricity use.
     */
    public double calcElectricityCO2(double avgBill, double avgPrice) {
        return (avgBill / avgPrice) * 1.37 * 12;
    }
}

---

每月总计始终为0.0。因此，您的函数返回0.0/sum

输出为0，因为您写入：

double monthlyTotal = 0.0;

我想你想

 return  sum/monthlyPrice.size();

---

您的输出方法在哪里？你做了大量的计算，但从来没有做过任何事情来显示它们。如何调用这些方法？看起来您提供了一个片段。这是您编写的完整代码吗？您没有提供调用此方法并执行输出的代码。我确实返回了（avgBill/avgPrice）*1.37*12；是这样吗？或者显示输出是我做错的部分？是的，这是我做的整个程序。这是一个问题，但我不确定OP在说输出为0时所指的是什么。由于没有调用输出方法，我猜0只是程序的返回代码。你完全正确。我以为在某个地方会有一份打印的声明，然后在数学上有了一个隧道式的视野。

 return  sum/monthlyPrice.size();