Question

我有三个问题。

1）我正在尝试打印一系列电子书。该阵列长25个元素，我已经在其中放置了6个电子书。当我打印时，它打印每个电子书25次，而不是只打印一次。

2）我的程序结束时输出的是在我想要的打印语句之前打印一个大的十进制数

3）如何实现JOptionPane或其他类，将ALL输出打印到一个对话框中？

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

我认为问题出在addEbook课程中的EbookLibrary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，您还要递增total_cost和count。我假设您只想将一次添加到数组并在执行此操作之前验证数组是否已满。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
}

Answer 2

十进制数是由于这一行： System.out.printf（＆＃34;％d％f％s％n＆＃34;，aLibrary.getCount（），aLibrary.getCost（），aLibrary.toString（））;

%d显示一个整数，但%f显示一个浮点数;删除它，这部分将工作。

你的addEbook功能也错了;它用一个电子书填充整个数组，并每次显示它（导致它显示25次）。

打印数组和toString时输出问题

2 个答案: