java - 为什么这个方法的返回值总是0？

Question

因此，无论该方法的输入如何，我都会不断收到 0 的答案。当我输入 6 个月、100 储蓄金额和 0.05 利率时，它应该给我 608.81 但响应是0。我觉得这可能是我的 for 循环或我设置的参数弄乱了它。我已经尝试了所有我能想到的有关 for 循环的方法。代码如下:

import java.text.DecimalFormat;
import javax.swing.JOptionPane;

public class FifthAssignment2 {

    static double savingAmount = 0.0; // the 2 given static doubles
    static double annualInterestRate = 0.0;
    static int numberOfMonth;
    static double sixthMonth = 0.0;;

    public static double compoundValueMethod(double savingAmount, double annualInterestRate, int NumberOfMonth) {

        {
        DecimalFormat formatter = new DecimalFormat(".00");

        double monthlyInterestRate = annualInterestRate / 12;

        if (savingAmount < 0)
            if (annualInterestRate < 0) {
                JOptionPane.showMessageDialog(null, "Error. Both of your values are negative!");
                System.exit(0);
            }

        if (savingAmount < 0) {
            JOptionPane.showMessageDialog(null, "Error. Your savings amount is negative!");
        }

        else if (annualInterestRate < 0) {
            JOptionPane.showMessageDialog(null, "Error. Your annual interest rate is negative!");
        }

        else {
            for (int i = 0; i < numberOfMonth; i++) {
                sixthMonth = ((savingAmount+sixthMonth) * (1 + monthlyInterestRate));
            }
        }
        return sixthMonth;
        }
    }

    public static void main(String[] args) {

        DecimalFormat formatter = new DecimalFormat(".00");

        int numberOfMonth;                                                  


        String NOM = JOptionPane.showInputDialog("How many months? ");
        numberOfMonth = Integer.parseInt(NOM);

        String SA = JOptionPane.showInputDialog("What is your savings amount? "); 

        savingAmount = Double.parseDouble(SA); 

        String AIR = JOptionPane.showInputDialog("What is the annual interest rate? "); // Window pops up
        annualInterestRate = Double.parseDouble(AIR); 

        {
            JOptionPane.showMessageDialog(null, "Your total compounded value after 6 months is "
                    + compoundValueMethod(savingAmount, annualInterestRate, numberOfMonth));
        }

    }
}

Answer 1

您将以下变量传递给您的方法:

public static double compoundValueMethod(double savingAmount,
                                         double annualInterestRate,
                                         int NumberOfMonth)

请注意，请在方法中使用静态变量 numberOfMonth，而不是传递的 NumberOfMonth 参数(Java 中的变量名称区分大小写)。 numberOfMonth 默认初始化为 0，因此不会进入 for 循环并且该方法返回 0。

您应该消除静态变量并仅使用局部变量。如果您一开始就这样做，您会收到编译错误，这将使您更容易找到错误。