Question

我现在完全失败了。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并更新Balance，因为帐户的利息是累计的：< / p>

对于第一个账户10,002，每月累计利息，年利率为1.2％。
对于第二个账户10,003，每季度累计利息，年利率为4％。

为了做到这一点，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是主类。

在SavingsAccount我有setAnnualInterestRate()中调用的方法SavingsAccountDriver。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。如果有人可以帮我解决这个问题，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;
            }
        }*/
    }
}

SavingsAccount ：

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

您可能希望将getInterest添加为抽象方法，并将SavingsAccount声明为抽象类。那么你将拥有编译器已知的方法来调用，你将被迫在子类中提供正确的实现

Answer 2

如果您要将getInterest()和SavingsAccount声明为saver1类型，则应在父类 - saver2中声明SavingsAccount方法。

您展示的方式，该方法仅适用于声明为FlexibleSavingsAccount的类。

由于您将其声明为SavingsAccount，因此您只能访问该类＆＃39;方法

子类可以访问父类的方法，但不能反过来。

Answer 3

您已将实例化的储蓄帐户声明为SavingsAccount类型。他们无法访问getInterest()方法，因为它位于子级类FlexibleSavingsAccount中。

您需要将它们实例化为您希望它们实际存在的实际储蓄帐户：

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

现在saver1将能够访问getInterest()。

额外的想法：

将父SavingsAccount编码为接口可能更好。然后，您将在此界面中声明您的getInterest()方法，同时将方法内容的详细信息留给您的子类。

SavingsAccount：

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，这有一个额外的好处，即您将实例编码为SavingsAccount接口，这对于将来验证代码总是一个好主意。

将变量传递给扩展类和调用方法

3 个答案: