Getter/Setter（组合、Java、HW）

Question

我有一个名为 Person 的类，基本上如下所示：

public class Person
{
    String firstName;
    String lastName;
    String telephone;
    String email;

    public Person()
    {
       firstName = "";
       lastName = "";
       telephone = "";
       email = "";
    }

    public Person(String firstName, String lastName, String telephone, String email) 
    {
        this.firstName = firstName;
        this.lastName = lastName;
        this.telephone = telephone;
        this.email = email;
    }

    public String getFirstName()
    {
        return firstName;
    }

    public void setFirstName(String firstName)
    {
        this.firstName = firstName;
    }
 ....

使用该类，我设置了一个名为 Loan 的抽象类，如下所示：

public abstract class Loan
{   
    public void setClient(Person client)
    {
        this.client = client;
    }

    public Person getClient()
    {
        return client;
    }

    public void setLoanId(int nextId)
    {
        loanId = nextId;
        nextId++;
    }

    public int getLoanId()
    {
        return loanId;
    }

    public void setInterestRate(double interestRate)
    {
        this.interestRate = interestRate;
    }

    public double getInterestRate()
    {
        return interestRate;
    }

    public void setLoanLength(int loanLength)
    {
        this.loanLength = loanLength;
    }

    public int getLoanLength()
    {
        return loanLength;
    }

    public void setLoanAmount(double loanAmount)
    {
        this.loanAmount = loanAmount;
    }

    public double getLoanAmount(double loanAmount)
    {
        return loanAmount;
    }

    private Person client;
    private int loanId;
    private double interestRate;
    private int loanLength;
    private double loanAmount;
    private static int nextId = 1;

}

我必须使用 CarLoan 扩展 Loan 类，它看起来像：

public class CarLoan extends Loan
{
    public CarLoan(Person client, double vehiclePrice, double downPayment, double salesTax,
                    double interestRate, CAR_LOAN_TERMS length)
    {
        super.setClient(client);
        super.setInterestRate(interestRate);
        this.client = client;
        this.vehiclePrice = vehiclePrice;
        this.downPayment = downPayment;
        this.salesTax = salesTax;
        this.length = length;

    }

    public void setVehiclePrice(double vehiclePrice)
    {
        this.vehiclePrice = vehiclePrice;
    }

    public double getVehiclePrice()
    {
        return vehiclePrice;
    }

    public void setDownPayment(double downPayment)
    {
        this.downPayment = downPayment;
    }

    public double getDownPayment()
    {
        return downPayment;
    }

    public void setSalesTax(double salesTax)
    {
        this.salesTax = salesTax;
    }

    public double getSalesTax()
    {
        return salesTax;
    }

    public String toString()
    {
        return getClass().getName() + "[vehiclePrice = " + vehiclePrice + '\n' 
                                        + "downPayment = " + downPayment + '\n'
                                        + "salesTax = " + salesTax 
                                        + "]";
    }

    public enum CAR_LOAN_TERMS {TWO_YEAR, THREE_YEAR, SIX_YEAR};
    private double vehiclePrice;
    private double downPayment;
    private double salesTax;

几个问题。

(a) 鉴于我在 Person 类中的内容，我在 Loan 类中对 setClient 所做的操作是否正确？ (egthis.client = client)

(b) 我可以在一个方法中调用 super 两次吗？我必须从 CarLoan 类的构造函数中设置 Loan 类的两个属性，我认为这将是一种方法。

(c) 是否必须在构造函数或 getter/setter 方法中以不同方式设置枚举类型的属性？我在 CarLoan 类中收到 (this.length = length) 错误，并且我不确定应如何设置枚举值。谢谢！

Answer 1

好的，按顺序：

1. setClient 看起来非常好。没有什么问题。但是，您希望避免直接在 CarLoan 构造函数中设置 this.client - 您已经在调用 setClient （感谢 @Gabriel 和 @埃斯）。
2. 当然，您可以根据需要使用 super 访问父类方法。您需要小心的是调用超类的构造函数，您只能在子类构造函数的开头执行一次。 超级！=超级()。
3. 不，this.length = length 没问题。问题是您没有名为 length 的字段。您可能想添加其中之一。

Answer 2

1) 按照惯例，将类的属性声明放在​​构造函数和方法之前。

2) CarLoan 类中的语句 this.client = client; 会出现编译错误，因为 client 字段在Loan 类。 （无论如何，该语句是多余的，因为您只是使用 setter 初始化了相同的字段......尽管希望您已经知道这一点。）

3）初始化超类字段的更好方法是将参数传递给超类构造函数。例如：

public abstract class Loan
{   
    private Person client;
    private double interestRate;

    public Loan(Person client, double interestRate) {
        this.client = client;
        this.interestRate = interestRate;
    }
    ...
}

public class CarLoan extends Loan
{   
    ...

    public CarLoan(Person client, double vehiclePrice, double downPayment, double salesTax,
                    double interestRate, CAR_LOAN_TERMS length)
    {
        super(client, interestRate); 
        this.vehiclePrice = vehiclePrice;
        ...
    }
}

这种方法更好的原因是 Loan 类负责其初始化，并且不依赖于各种子类构造函数来完成这项工作。 （如果您向 Loan 添加额外的字段，并将相应的参数添加到 Loan 构造函数中，编译器会提醒您修改所有子类构造函数以提供初始值super 构造函数链接。如果子类负责在初始化期间设置基类中的字段，则编译器不会注意到您忘记添加新的 setter 调用。）

4) 如果您这样做在构造函数中调用方法时，最好确保它们不能在子类中被重写。 （不……重写方法并非完全错误，但有些事情可能会出现严重错误。在构造函数中调用可能可重写的方法会使您的代码变得脆弱。）

5) 如果这是生产代码，请使用float 或 double 来表示货币值将是一个很大的禁忌！

Answer 3

回答问题（c），我认为您收到错误，因为您需要在那里定义长度以及已经定义的变量。