Question

我有一个名为Person的类，基本上看起来像：

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所做的是正确的吗？（egthis.client = client）

（b）我可以在方法中拨打超级两次吗？我必须从CarLoan类的构造函数中设置Loan类的两个属性，我认为这是一种方法。

（c）您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类中得到（this.length = length）错误，我不确定应该如何设置枚举值。谢谢！

Answer 1

好的，按顺序：

setClient看起来很好。它没有错。但是，您希望避免直接在this.client构造函数中设置CarLoan - 您已经在调用setClient（感谢@Gabriel和@Aeth）。
当然，您可以根据需要使用super访问父类方法。你需要注意的是调用超类'构造函数，你只能做一次并在子类'构造函数的开头。 super != super()。
不，this.length = length没问题。问题是您没有名为length的字段。您可能想要添加其中一个。

Answer 2

1）在构造函数和方法之前放置类的属性的声明是常规的。

2）this.client = client;类中的语句CarLoan将给出编译错误，因为client类中Loan字段被声明为私有。（而且这个陈述无论如何都是多余的，因为你刚刚使用setter初始化了相同的字段......虽然期望你已经知道了。）

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，并且不依赖于执行该作业的各种子类构造函数。（如果向Loan添加一个额外字段并将相应参数添加到Loan构造函数，编译器会提醒您修改所有子类构造函数以在super中提供初始值如果子类负责在初始化期间设置基类中的字段，那么编译器将不会注意到您忘记添加新的setter调用。）

4）如果你在构造函数中调用方法，最好确保它们不能在子类中重写。（不......重写方法并不完全错误，但有些事情可能会出现严重错误。在构造函数中调用潜在的可覆盖方法会使代码变得脆弱。）

5）如果这是生产代码，使用float或double代表货币价值将是一个很大的禁忌！

Answer 3

回答问题（c），我认为你得到了错误，因为你需要在那里定义长度以及你已经定义的变量。

Getter / Setter（组合，Java，HW）

3 个答案: