Question

想法是打印出一条简单的行，说明书名，作者和价格。但是，即使构造了Book对象，我似乎也无法返回任何值。

我正在构建Book类，Author类，并使用测试器来运行程序。

这是我在看的东西：

package book;

public class Book {

    String title;
    Author author;
    double price;

    public Book(String title, Author author, double price){}

    public Book(){}

    public void setbookTitle(String title) {
        this.title = title;
    }

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

    public String getTitle() {
        return title;
    }

    public Author getAuthor() {
        return author;
    }

    public double getPrice() {
        return price;
    }

}

package book;

public class Author {

    String name;
    String email;
    char gender;

    public Author(String name, String email, char gender){
    }

    public String getName() {
        return name;
    }

    public String getEmail(){
        return email;
    }

    public char getGender(){
        return gender;
    }

    public void setName(String name) {
        this.name = name;
    }

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

    public void setGender(char gender) {
        this.gender = gender;
    }

    @Override
    public String toString(){
        return name;
    }



}

package book;

public class BookTester {

    public static void main(String[] args) {

    Author author1 = new Author("Horstmann", "horstmann@gmail.com", 'm');
    Book book1 = new Book("Big Java", author1, 60);

    Double number = book1.getPrice();
        System.out.println(number);

    System.out.println ("The Book information is: ");
    System.out.println(book1.getTitle() + book1.getAuthor() + book1.getPrice());


    }

}

任何建议将不胜感激！

Answer 1

它为null，因为您没有在Book＆Author的构造函数中做任何事情：

public Author(String name, String email, char gender){
}

public Book(String title, Author author, double price){
}

您需要设置值并将其更新为对象的值：

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

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

Answer 2

您应该将构造函数更改为

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

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

值始终在构建对象后返回null

2 个答案: