java - 打印数组和 toString 时的输出问题

Question

我有三个问题。

1) 我有一系列电子书想要打印。该数组有 25 个元素长，我在其中放置了 6 本书。当我打印时，它会打印每本电子书 25 次，而不是只打印一次。

2)我在程序末尾有输出，在我想要的打印语句之前打印一个大的十进制数字

3) 如何实现 JOptionPane 或其他一些类，以将所有输出打印到一个对话框上？

import javax.swing.JOptionPane; // dialog box

public class Ebook
{
    private String author = "";
    private String title = "";
    private double price = 0.0;
    private String isbn = "";


        public Ebook(String author, String title, double price, String isbn) // ebook constructor 
        {
            this.author = author;
            this.title = title;

            if (price > 0) // validate non-negative price
                this.price = price;

            else 
            {   
                this.price = 0.0; 
                    System.out.println("Invalid price");
            }

            if (isbn.length() == 10 || isbn.length() ==  13) // isbn length must be exactly 10 or 13
                this.isbn = isbn;

            else
                this.isbn = "None";
        }   

        public void setPrice(double price)
        {
            if (price < 0) // vallidate
            {
                System.out.println("Invalid price");
            }

            else
                this.price = price;
        }

        public double getPrice()
        {
            return price;
        }

        public void setAuthor(String theAuthor)
        {
            this.author = theAuthor;
        }

        public String getAuthor()
        {
            return author;
        }

        public void setIsbn(String isbn)
        {
            if (isbn.length() == 10 || isbn.length() ==  13) // validate
            {
                this.isbn = isbn;
            }
            else 
                isbn = "None";
        }

        public String getIsbn()
        {
            return isbn;
        }

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

        public String getTitle()
        {
            return title;
        }

        public String toString()
        {
            return String.format("Author: %s%nTitle: %s%nPrice: $%.1f%nISBN: %s%n",
                author,title,price,isbn);
        } 
} // This was made by ------

import javax.swing.JOptionPane; // dialog box

public class EbookLibrary
{
    private int count = 0;
    private double total_cost = 0.0;


    Ebook[] ebooks = new Ebook[25]; // array of ebook objects

    public EbookLibrary() // no argument constructor for ebooklibrary object in library test
    {

    }
    public int getCount() // total number of ebooks
    {
        return count;
    }
    public double getCost() // sum of all ebooks
    {
        return total_cost;
    }
    public String toString() // formatted string with the number and cost of all ebooks
    {
        return String.format("Ebook count: %d%nTotal Cost: $%.1f", count, total_cost);
    }
    public void addEbook(String author, String title, double price, String isbn) // adds ebooks to the array
    {
        Ebook anEbook = new Ebook(author,title,price,isbn); // not sure if this is a "constructor", but I think it is

        for (int counter = 0; counter < ebooks.length; counter++) // for the length of the array, add ebook
        {
            ebooks[counter] = anEbook; // for each counter, add the ebook 
                total_cost += price;
                    count++; // used to find the total number of ebooks
                        System.out.printf("%s%n", ebooks[counter]);

        }


    } 



} // This was made by -----

import javax.swing.JOptionPane; // dialog box

public class EbookLibraryTest
{
    public static void main(String[] args)
    {

        EbookLibrary aLibrary = new EbookLibrary(); // EbookLibrary object for calling addEbook

        //ebook objects, more can be added to test set, get methods
        aLibrary.addEbook("Blah", "What", 88.8, "1234567891");
        aLibrary.addEbook("Thing Do", "What What", 45.0, "1234567891111");
        aLibrary.addEbook("Stephen King","The Thing",1.1, "1234567891");
        aLibrary.addEbook("Robert","A Title", -1.0, "1234567891"); // test invalid price, should return 0.0 and "invalid price"
        aLibrary.addEbook("Tom","Bad Title", 33.1, "1234567891111");
        aLibrary.addEbook("Bob", "FML and Other Acronyms", 25.0, "1"); // test ISBN value, should return "None"




        System.out.printf("%d%f%s%n", aLibrary.getCount(), // call methods, print with toString
            aLibrary.getCost(), aLibrary.toString());

        System.out.println("Programmed by -----");

    }
}

Answer 1

我相信问题出在 EbookLibrary 类中的 addEbook 方法。每次添加新的 Ebook 时，都会用它填充整个 ebooks 数组。在每次迭代中，您还会增加 total_cost 和 count。我假设您只想将其添加到数组中一次，并在执行此操作之前验证数组未满。试试这个。

public void addEbook(String author, String title, double price, String isbn) // adds ebooks to the array
{
    if(count==ebooks.length-1) {
        return;
    }
    Ebook anEbook = new Ebook(author,title,price,isbn);

    ebooks[count] = anEbook;
    total_cost += price;
    System.out.printf("%s%n", anEbook);
    count++; // used to find the total number of ebooks
}