Question

在Book类中创建一个作者对象时遇到了麻烦。这确实是Homework，我自己想出了所有的方法，现在已经盯着这个作业2个小时了。任何提示提示将不胜感激。我相信我只允许这个带有3个参数的Author构造函数，否则我只会创建一个没有参数的Author构造函数，问题就会消失。

public class Author {

    protected String name;
    protected String email;
    protected char gender;

    public Author(String name, String email, char gender)
    {
        this.name = name;
        this.email = email;
        this.gender = gender;
    }

    public String getName()
    {
        return name;
    }

    public String getEmail()
    {
        return email;
    }

    public void setEmail(String email)
    {
        this.email = email;
    }

    public char getGener()
    {
        return gender;
    }

    public String toString()
    {
        return ( name + "(" + gender + ")@" + email);
    }


}

public class Book extends Author{

    private String name;
    private Author author;
    private double price;
    private int qtyInStock = 0;

    public Book(String name, Author author,Double price)
    {
        this.author = new author;
        this.name = name;
        this.price = price;

    }

    public Book(String name, Author author, double price, int qtyInStock)
    {

        this.name = name;
        this.author = author;
        this.price = price;
        this.qtyInStock = qtyInStock;
    }

    public String getName()
    {
        return name;
    }

    public Author getAuthor()
    {
        return author;
    }

    public double getPrice()
    {
        return price;
    }

    public void setPrice(double price)
    {
        this.price = price;
    }

    public int getQtyInStock()
    {
        return qtyInStock;
    }

    public void setQtyInStock(int qtyInStock)
    {
        this.qtyInStock = qtyInStock;
    }

    public String toString()
    {
        return (name + " by " + author + "(" + super.gender + ")at" + super.email);
    }
}

Answer 1

如果没有this.author = author;关键字，则应为new。

您正在构造函数中分配Author对象，而不是创建新对象。

顺便说一句，Book继承自Author，这意味着它已具有Author功能。您不必将其保存为成员。

Answer 2

Book extends Author似乎很奇怪。 Book不是Author。

我认为您要做的是创建一个Book对象，其中Author，但您已经将Author传递给Book构造函数，所以有什么问题？

class Book {
    public Book(String title, Author author) {
        this.title = title;
        this.author = author;
    }
}

如果您想知道如何创建Author，只需在将其传递给Book之前创建它。

Author author = new Author("bob", "bob@email.com", 'm');
Book book = new Book("some title", author);

这有意义吗？

Answer 3

您在Author继承Book，继承为is a relationship，意味着Book is a Author在现实世界的情况下不正确，您需要has a relation感觉，Book has a Author。

所以不要在Book中扩展作者，保留一个作者的字段，就像你已经做过的那样。改变你的设计。

Answer 4

您的代码中存在多个错误：

正如@Guy所说，您需要为作者分配this.author = author，而不是new关键字。
您通过在Author类中包含同名变量来隐藏Book类中的name变量。从Book类中删除该变量以及getter和setter方法。
您没有参数构造函数，因此您必须通过调用Book来调用super(name, email, gender);类中的父构造函数。

Answer 5

您应该使用author替换新作者，同样在调用子类型的构造函数时，默认情况下会调用Parent类的默认构造函数。所以你需要在父类中指定一个默认构造函数，或者为了防止它在子类构造函数中显式调用父类的参数构造函数。

Answer 6

除了改为this.author = author。您还需要将super(name, name, 'M');添加到Book类的两个构造函数中。

Answer 7

public class Book extends Author{

private String name;
//private final String email;
// private char gender;
private Author author;// = new Author(name,super.email,super.gender);
private double price;
private int qtyInStock = 0;

public Book(String name, Author author,double price)
{
    //super();
    this.author = author;// new Author(name,super.email,super.gender);
    super.name = author.getName();
    super.gender = author.getGender();
    super.email = author.getEmail();
    this.name = name;
    this.price = price;

}

public Book(String name, Author author, double price, int qtyInStock)
{
    this.author = author;
    super.name = author.getName();
    super.gender = author.getGender();
    super.email = author.getEmail();
    this.name = name;
    this.price = price;
    this.qtyInStock = qtyInStock;
}

public String getName()
{
    return name;
}

public Author getAuthor()
{
    return author;
}

public double getPrice()
{
    return price;
}

public void setPrice(double price)
{
    this.price = price;
}

public int getQtyInStock()
{
    return qtyInStock;
}

public void setQtyInStock(int qtyInStock)
{
    this.qtyInStock = qtyInStock;
}

public String toString()
{
    return (super.name + " by " + this.name + "(" + super.gender + ")at" + super.email);
}

还将此添加到作者类

 public Author()
{

}

java在子类中创建一个对象

7 个答案: