打印陣列時出現輸出問題toString

Question

我有三個問題。

1）我有一組電子書，我試圖打印。該陣列有25個元素，我已經放置了6個電子書。當我打印時，它會打印每個電子書25次，而不是一次。

2）我有我的計劃是我想要的打印語句

3）如何實現的JOptionPane，或者一些其他的課前打印大量的十進制數年底輸出，打印所有輸出到一個對話框？

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

我相信這個問題是在你的EbookLibrary類的addEbook方法。每次添加新的Ebook時，都會用它填充整個ebooks陣列。在每次迭代中，您還將增加total_cost和count。我假設你只想將它添加一次到數組中，並在這樣做之前確認數組未滿。嘗試這個。

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

的十進制數是由於這一行： System.out.printf（ 「％d％F％S％N」，aLibrary.getCount（），aLibrary.getCost（），aLibrary.toString（ ））;

%d顯示一個整數，但%f顯示一個浮點數;刪除它，這部分將工作。

你的addEbook函數也是錯誤的;它使用單個電子書填充整個陣列，並每次顯示（導致顯示25次）。