Question

我试图在一个对话框中打印书名和isbn。我对java很新，我不能让toString()工作，我需要帮助。

  public class Book
    {
        private String title;
        private String author;
        private String isbn;
        private Double price;
        private Publisher publisher;

    public Book()
    {
        setTitle("");
        setAuthor("");
        setIsbn("");
        setPrice(0.0);
        setPublisher(new Publisher());
    }

    public Book(String t, String a, String i, double p, Publisher n)
    {

        setTitle(t);
        setAuthor(a);
        setIsbn(i);
        setPrice(p);
        setPublisher(n);
    }

    public void setTitle(String t)
    {
        title = t;
    }

    public String getTitle()
    {
        return title;
    }

    public void setAuthor(String a)
    {
        author = a;
    }

    public String getAuthor()
    {
        return author;
    }

    public void setIsbn(String i)
    {
        isbn = i;
    }

    public String getIsbn()
    {
        return isbn;
    }

    public void setPrice(double p)
    {
        price = p;
    }

    public double getPrice()
    {
        return price;
    }

    public void setPublisher(Publisher n)
    {
        publisher = n;
    }

    public Publisher getPublisher()
    {
        return publisher;
    }

    public double calculateTotal(int quantity)
    {
        return(price * quantity);
    }

    public String toString()
    {
        return( "Title" + title + "Author" + author + "Isbn" + isbn
            + "Price" + price + "Publisher" + publisher.toString());
    }

}



import javax.swing. JOptionPane;

public class BookTest
{
    public static void main(String args[])
    {
        String dataArray[][] = {{"Abraham Lincoln Vampire Hunter","Grahame-Smith","978-0446563079","13.99", "Haper", "NY"},
                    {"Frankenstein","Shelley","978-0486282114","7.99","Pearson", "TX"},
                    {"Dracula","Stoker","978-0486411095","5.99","Double Day", "CA"},
                    {"Curse of the Wolfman"," Hageman","B00381AKHG","10.59","Harper", "NY"},
                    {"The Mummy","Rice","978-0345369949","7.99","Nelson", "GA"}}; //book info




        Book bookArray[] = new Book[dataArray.length];

        int quantityArray[] = {12, 3, 7, 23, 5};

        for (int i = 0; i < dataArray.length; i++)
        {
            bookArray[i] = new Book(dataArray[i][0], dataArray[i][1], dataArray[i][2], 
                Double.parseDouble(dataArray[i][3]), new Publisher(dataArray[i][4], dataArray[i][5]));
        }


        for (int i = 0; i < bookArray.length; i++)
        {
            bookArray[i].calculateTotal(quantityArray[i]);



        }


            JOptionPane.showMessageDialog(null, Book.toString());

    }




}

Answer 1

当您通过类的名称限定方法而不是引用该类的实例的变量时，您尝试在类Book上调用名为toString的静态方法。您的Book类中未定义此类方法。

相反，你应该调用的是书籍实例上的toString（），例如bookArray中的那些实例

例如，这里是在循环内调用的字符串：

    for (int i = 0; i < bookArray.length; i++)
    {
        Book b = bookArray[i];
        b.calculateTotal(quantityArray[i]);
        //Using JOptionPane.showMessageDialog here only for an example, this probably isn't the OPs intent
        JOptionPane.showMessageDialog(null, b.toString();); 
    }

有关静态工作方式的参考，请参阅here和here。

有关覆盖toString的额外阅读，我建议您使用short chapter in Effective Java, 2nd Edition.

Answer 2

做的时候

JOptionPane.showMessageDialog(null, Book.toString());

您尝试静态调用toString，Book未定义。{/ p>

您需要从Book实例调用它。

Answer 3

你的代码看起来很模糊。

toString（）的问题在以下代码部分

中

for (int i = 0; i < bookArray.length; i++)
{
    bookArray[i].calculateTotal(quantityArray[i]);
}
JOptionPane.showMessageDialog(null, Book.toString());

当您调用Book.toString（）时，实际上是从类Book调用该方法。要打印书籍的内容，您应该在for循环中插入该代码并使用书籍实例。

for (int i = 0; i < bookArray.length; i++)
{
    bookArray[i].calculateTotal(quantityArray[i]);
    JOptionPane.showMessageDialog(null, bookArray[i].toString());
}

PS：请使用IDE及其AutoFormat实用程序。

对于Eclipse，您可以使用 Control + Shift + F 和Intellij IDEA Control + Alt + L

我如何从另一个类打印我的toString

3 个答案: