我如何返回答案？

Question

public class BankAccount {

  private static final double annualInterestRate = 1.5;

  private static double accountBalance = 150;

  private static double MonthlyInterest;

  public static void main(String[] args) {

    // TODO Auto-generated method stub

    calculateMonthlyInterest();   

    System.out.println(MonthlyInterest);

  }

  public static double calculateMonthlyInterest() 

  {

    double MonthlyInterest = (accountBalance * annualInterestRate);

    return MonthlyInterest;

  }

}

这是我的代码，我正在尝试返回MonthlyInterest，但是当我打印出来时，我得到 0 而不是 225

Answer 1

问题您正在以一些非常奇怪的方式混合静态和非静态功能。这是您的代码中发生的事情：private static double MonthlyInterest;您在类上创建一个静态变量。由于它是一个原始的double，它默认为 storage 0。此外，变量名称应以小写字母开头。这应该是monthlyInterest。它不会破坏任何东西，但它是区分类名和变量名的标准 Java 约定。calculateMonthlyInterest();你调用calculateMonthlyInterest()方法。double MonthlyInterest = (accountBalance * annualInterestRate);return MonthlyInterest;您计算每月利息，将其存储在新变量中，然后返回。请注意，此代码不会更新MonthlyInterest您的静态变量。相反，您创建的局部变量会“遮蔽”静态变量，并优先于它。calculateMonthlyInterest();System.out.println(MonthlyInterest)您丢弃从未使用过的返回值，然后打印出MonthlyInterest从未从初始值零改变的静态。您可以采用以下两种不同的方法来使您的代码正常工作：使用静态变量public class BankAccount {    private static final double annualInterestRate = 1.5;    private static double accountBalance = 150;    private static double monthlyInterest;    public static void main(String[] args) {        calculateMonthlyInterest();        System.out.println(monthlyInterest);    }    public static void calculateMonthlyInterest() {        monthlyInterest = (accountBalance * annualInterestRate);    }}使用局部变量public class BankAccount {    private static final double annualInterestRate = 1.5;    private static double accountBalance = 150;    public static void main(String[] args) {        double monthlyInterest = calculateMonthlyInterest();        System.out.println(monthlyInterest);    }    public static double calculateMonthlyInterest() {        return accountBalance * annualInterestRate;    }}

Answer 2

public class BankAccount {private static final double annualInterestRate = 1.5;private static double accountBalance = 150;private static double MonthlyInterest;public static void main(String[] args) {    // TODO Auto-generated method stub    calculateMonthlyInterest();    System.out.println(MonthlyInterest);}public static void calculateMonthlyInterest() {    MonthlyInterest = accountBalance * annualInterestRate ;}}

Answer 3

您正在定义 MonthlyInterest 2 次：在 BankAccount 类上关于 calculateMonthlyInterest 方法这些是两个具有相同名称的不同变量，因为变量范围是您分配的一个（accountBalance * yearInterestRate）是 calculateMonthlyInterest 方法的本地变量，因此这不会影响在 te BankAccount 类上定义的变量您可以解决此问题，将 calculateMonthlyInterest 的返回值分配给类范围上的 MonthlyInterest：private static final double annualInterestRate = 1.5;private static double accountBalance = 150;private static double MonthlyInterest;public static void main(String[] args) {  MonthlyInterest = calculateMonthlyInterest();  System.out.println(MonthlyInterest);}public static double calculateMonthlyInterest() {  return  (accountBalance * annualInterestRate);}或不在方法上定义 MonthlyInterest：private static final double annualInterestRate = 1.5;private static double accountBalance = 150;private static double MonthlyInterest;public static void main(String[] args) {  calculateMonthlyInterest();  System.out.println(MonthlyInterest);}public static double calculateMonthlyInterest() {  MonthlyInterest = (accountBalance * annualInterestRate);}

Answer 4

您不需要返回任何值，因为您将其保存在静态变量中。如果您希望您的方法实际返回一个值，请将其直接分配给MonthlyInterest. 你也不需要MonthlyInterest在你的方法中声明，因为那时值被分配给局部变量，并且 printline 从类静态变量中获取值。private static final double annualInterestRate = 1.5;private static double accountBalance = 150;private static double MonthlyInterest;public static void main(String[] args) {    // TODO Auto-generated method stub    MonthlyInterest = calculateMonthlyInterest();    System.out.println(MonthlyInterest);}public static double calculateMonthlyInterest() {    return  (accountBalance * annualInterestRate);}