将变量传递给扩展类和调用方法

Question

我现在完全不知所措。 我正在尝试开发一个程序，该程序将显示两个储蓄帐户的Months ， Account #和Balance ，并在应计利息时更新Balance ：

• 对于第一个帐户，每月应计10,002利息，年利率为1.2％。
• 对于第二个帐户，每季度应计利息10,003，年利率为4％。

为此，我必须设计四个单独的类。 SavingsAccount ， SavingsAccountDriver ， FlexibleSavingsAccount和CDSavingsAccount 。 SavingsAccount是FlexibleSavingsAccount和CDSavingsAccount的父类。 SavingsAccountDriver是Main类。

在SavingsAccount我有一个方法setAnnualInterestRate()在SavingsAccountDriver调用。 此方法设置每个帐户的利率。 我遇到的问题是将此值传递给扩展类FlexibleSavingsAccount和CDSavingsAccount以便我可以通过添加每个帐户的利率来更新余额。 如果有人可以帮助我完成这项工作，我将不胜感激。

SavingsAccountDriver ：

public class SavingsAccountDriver {
    public static void main (String[] args) {
        SavingsAccount saver1 = new SavingsAccount(10002, 2000); //create new SavingsAccount object
        SavingsAccount saver2 = new SavingsAccount(10003, 3000); //create new SavingsAccount object

        saver1.setAnnualInterestRate(.012); //sets AnnualInterestRate for 'saver1' object
        saver2.setAnnualInterestRate(.04); //sets AnnualInterestRate for 'saver2' object

        System.out.println("\nMonthly balances:\n");
        System.out.println("Month " + " Account# " + " Balance " + "      " + " Month " + " Account# " + " Balance ");
        System.out.println("----- " + " -------- " + " ------- " + "      " + " ----- " + " -------- " + " ------- ");


        System.out.println(saver1.getAccountNumber() + " / " + saver1.getBalance() + " / " + saver1.getInterest());
        System.out.println(saver2.getAccountNumber() + " / " + saver2.getBalance() + " / " + saver2.getInterest());

        /*for(int month = 0; month <= 12; month++) {
            switch(month) { // switch that outputs month, account number, and balance for both accounts (Some non-needed cases used to make output look cleaner)
                case 0:
                    System.out.println(month + "      " + saver1.getAccountNumber() + "     " + saver1.getBalance() + "         " + month + "      " + saver2.getAccountNumber() + "     " + saver2.getBalance());
                    break;
                case 4: 
                    saver1.addInterest();
                    //saver2.addInterest();

                    System.out.println(month + "      " + saver1.getAccountNumber() + "     " + saver1.getBalance() + "         " + month + "      " + saver2.getAccountNumber() + "     " + saver2.getBalance());
                    break;
                case 10:
                    saver1.addInterest();
                    //saver2.addInterest();

                    System.out.println(month + "     " + saver1.getAccountNumber() + "     " + saver1.getBalance() + "        " + month + "     " + saver2.getAccountNumber() + "     " + saver2.getBalance());
                    break;
                case 11:
                    saver1.addInterest();
                    //saver2.addInterest();

                    System.out.println(month + "     " + saver1.getAccountNumber() + "     " + saver1.getBalance() + "        " + month + "     " + saver2.getAccountNumber() + "     " + saver2.getBalance());
                    break;
                case 12:
                    saver1.addInterest();
                    //saver2.addInterest();

                    double totalBalance = saver1.getBalance() + saver2.getBalance();
                    System.out.println(month + "     " + saver1.getAccountNumber() + "     " + saver1.getBalance() + "        " + month + "     " + saver2.getAccountNumber() + "     " + saver2.getBalance());
                    break;
                default:
                    saver1.addInterest();
                    //saver2.addInterest();

                    System.out.println(month + "      " + saver1.getAccountNumber() + "     " + saver1.getBalance() + "        " + month + "      " + saver2.getAccountNumber() + "     " + saver2.getBalance());
                    break;
            }
        }*/
    }
}

储蓄账户 ：

public class SavingsAccount {
    // variables specific to SavingsAccount class
    public double annualInterestRate;
    private final int ACCOUNT_NUMBER;
    public double balance;

    //constructor with account number and balance parameters
    public SavingsAccount(int account_number, double balance) {
        this.ACCOUNT_NUMBER = account_number;
        this.balance = balance;
    }

    //returns account number
    public int getAccountNumber() {
        return this.ACCOUNT_NUMBER;
    }

    //returns balance
    public double getBalance() {
        return this.balance;
    }

    //sets interest rate
    public void setAnnualInterestRate (double interestRate) {
        this.annualInterestRate = interestRate;
    }
}

FlexibleSavingsAccount ：

public class FlexibleSavingsAccount extends SavingsAccount{

        public FlexibleSavingsAccount(int account_number, double balance) {
            super(account_number, balance);
        }

        //returns interest
        public double getInterest() {
            return annualInterestRate;  
        }
}

Answer 1

您可能需要将getInterest添加为抽象方法，并将SavingsAccount声明为抽象类。 那么您将拥有编译器已知的方法来调用，并且您将被迫在子类中提供正确的实现

Answer 2

如果要将saver1和saver2声明为SavingsAccount类型， saver2在父类SavingsAccount声明您的getInterest()方法。

按照您显示的方式，该方法仅适用于声明为FlexibleSavingsAccount类。

由于您将它们声明为SavingsAccount您只能访问该类的方法。

子类可以访问父类的方法，但不能相反。

Answer 3

您已将实例化的储蓄帐户声明为SavingsAccount类型。 他们将无法访问方法getInterest()因为该方法位于子类FlexibleSavingsAccount 。

您需要将它们实例化为希望它们实际成为的实际储蓄帐户：

FlexibleSavingsAccount saver1 = new FlexibleSavingsAccount(10002, 2000); //create new FlexibleSavingsAccount object

现在saver1将能够访问getInterest() 。

额外的主意：

更好的方法是将父SavingsAccount编码为接口。 然后，您将在此接口中声明getInterest()方法，同时将方法中的详细信息留给子类。

储蓄账户：

public interface SavingsAccount {
    public int getAccountNumber();
    public double getBalance();
    public void setAnnualInterestRate (double interestRate);
 }

然后实例化您的帐户：

SavingsAccount saver1 = new FlexibleSavingsAccount(10002, 2000); //create new FlexibleSavingsAccount object

请注意，这样做还有一个好处，就是您可以将实例声明为已编码到SavingsAccount接口，这对于将来验证代码始终是一个好主意。