打印阵列时出现输出问题toString

Question

我有三个问题。

1）我有一组电子书，我试图打印。该阵列有25个元素，我已经放置了6个电子书。当我打印时，它会打印每个电子书25次，而不是一次。

2）我有我的计划是我想要的打印语句

3）如何实现的JOptionPane，或者一些其他的课前打印大量的十进制数年底输出，打印所有输出到一个对话框？

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

我相信这个问题是在你的EbookLibrary类的addEbook方法。每次添加新的Ebook时，都会用它填充整个ebooks阵列。在每次迭代中，您还将增加total_cost和count。我假设你只想将它添加一次到数组中，并在这样做之前确认数组未满。尝试这个。

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

的十进制数是由于这一行： System.out.printf（ “％d％F％S％N”，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函数也是错误的;它使用单个电子书填充整个阵列，并每次显示（导致显示25次）。