Question

正如您在代码末尾看到的那样，我使用调用printLink方法的“list.printList”。它应该输出“书名：...书籍作者：......等”，它显示原始文本文件数据。我究竟做错了什么？此外，欢迎任何建议。感谢

编辑：这是文本文件的内容：

antrea ggfg 65 64
antrea ggfg 65 64
antrea ggfg 65 64
antrea ggfg 65 64

这是输出：

antrea ggfg 65 64
antrea ggfg 65 64
antrea ggfg 65 64
antrea ggfg 65 64

另外我认为令牌化器有问题。根据您的经验，我们应该如下所述做什么？

import java.io.* ;
import java.util.* ;

class Link
{
    public String isbn ;
    public String bookName ;
    public String bookAuthor ; 
    public String publicYear;
    public Link nextLink;

    public Link ()
    {

    }
    //Link constructor
    public Link(String bookNameIn, String bookAuthorIn, String isbnIn, String publicYearIn) 
    {
        setIsbn (isbnIn) ;
        setBookName (bookNameIn) ;
        setBookAuthor (bookAuthorIn) ;
        setPublicYear (publicYearIn) ;
        //isbn = isbnIn ;
        //bookAuthor = bookAuthorIn ;
        //publicYear = publicYearIn ;
    }

  // Set Methods
    public void setIsbn(String isbnIn)
    {
        isbn = isbnIn ;
    }

    public void setBookName(String bookNameIn)
    {
        bookName = bookNameIn ;
    }

    public void setBookAuthor(String bookAuthorIn)
    {
        bookAuthor = bookAuthorIn ;
    }

    public void setPublicYear(String publicYearIn)
    {
        publicYear = publicYearIn ;
    }

  // Get Methods
    public String getIsbn()
    {
        return isbn ;
    }

    public String getBookName()
    {
        return bookName;
    }

    public String getBookAuthor()
    {
        return bookAuthor ;
    }

    public String getPublicYear()
    {
        return publicYear ;
    }   

    //Print Link data
    public void printLink()
    {
            System.out.print("Book Name: " + getBookName() + "\n" + "Book's Author: " + getBookAuthor() + "\n" + "Year Published: " + getPublicYear() + "\n" + "ISBN: " + getIsbn() +"\n");
            System.out.println("") ;
    }
}

class LinkList 
{

    private Link first;

    //LinkList constructor
    public LinkList()
    {
            first = null;
    }

    //Returns true if list is empty
    public boolean isEmpty() 
    {
            return first == null;
    }

    //Inserts a new Link at the first of the list
    public void insert(String bookNameIn, String bookAuthorIn, String isbnIn, String publicYearIn) 
    {
            Link link = new Link(bookNameIn, bookAuthorIn, isbnIn, publicYearIn) ;
            link.nextLink = first;
            first = link;
    }

    //Deletes the link at the first of the list
    public Link delete() 
    {
            Link temp = first;
            first = first.nextLink;
            return temp;
    }

    //Prints list data
    public void printList()
    {
            Link currentLink = new Link() ;
            currentLink = first;
            while(currentLink != null) {
                    currentLink.printLink();
                    currentLink = currentLink.nextLink;
            }
            System.out.println("");
    }
}  

public class TheList 
{
    public static void main(String[] args) throws Exception
    {
            //Scanner kb = new Scanner (System.in); 
            LinkList list = new LinkList();
            File outputFile ;
            //int numberOfBooks = 0 ;

         // Create the new text file. If exists, it will continue to the next commands
            do
            {
                outputFile = new File("db.txt") ;

                    if(!outputFile.exists())
                    {
                        outputFile.createNewFile ();                    
                        System.out.println("The file was created as db.txt");
                        System.out.println("");
                    }

            }while (!outputFile.exists()) ;

            try
            {
                // Define which file to stream in from

                FileInputStream fileIn = new FileInputStream("db.txt") ;
                DataInputStream input = new DataInputStream (fileIn) ;
                BufferedReader br = new BufferedReader (new InputStreamReader (input)) ;
                String line ;

                // Read each line of the file

                while ((line = br.readLine()) != null)
                {
                    // insert code to break input to pieces
                    StringTokenizer tokenizer = new StringTokenizer(line) ;
                    while (tokenizer.hasMoreElements())
                    {
                        Link record = new Link() ;
                        record.setBookName(tokenizer.nextToken()) ;
                        record.setBookAuthor(tokenizer.nextToken()) ;
                        record.setIsbn(tokenizer.nextToken()) ;
                        record.setPublicYear(tokenizer.nextToken()) ;
                    }
                    System.out.println (line) ;
                }

                input.close() ;
            }catch (Exception e){
                System.err.println("Error. Could not read the file") ;
            }
            list.printList();


            /**list.insert(123456, "kostis", "kostis", 1900);
            list.insert(123456, "kostis", "kostis", 1900);
            list.insert(123456, "kostis", "kostis", 1900);
            list.insert(123456, "kostis", "kostis", 1900);
            list.insert(123456, "kostis", "kostis", 1900);
            **/



    }
}

Answer 1

我没有看到你在列表中添加任何内容，因此我假设printList()方法只打印一个空行。

原始文本文件数据似乎来自这一行：

System.out.println (line) ;

我认为你希望你的阅读代码是这样的（虽然我怀疑内在的同时会/应该是必要的）：

while ((line = br.readLine()) != null)
{
   // insert code to break input to pieces
   StringTokenizer tokenizer = new StringTokenizer(line) ;
   while (tokenizer.hasMoreElements())
   {
     String bookName = tokenizer.nextToken();
     String author = tokenizer.nextToken();
     String isbn = tokenizer.nextToken();
     String year = tokenizer.nextToken();

     list.insert(bookName, author, isbn, year) ;
   }
   System.out.println (line) ;
}

此外，这似乎很奇怪：

Link currentLink = new Link() ;
currentLink = first;

为什么不只是以下？

Link currentLink = first;

还有其他风格问题，但我暂时没有对这些问题发表评论。

Answer 2

你刚刚打印

System.out.println (line) ;

您永远不会将记录添加到列表中，因此行

list.printList();

什么都不做。在while循环中，您应该将记录添加到列表中。

以下内容：

while (tokenizer.hasMoreElements())
{
      Link record = new Link() ;
      record.setBookName(tokenizer.nextToken()) ;
      record.setBookAuthor(tokenizer.nextToken()) ;
      record.setIsbn(tokenizer.nextToken()) ;
      record.setPublicYear(tokenizer.nextToken()) ;
}

应该是：

    while (tokenizer.hasMoreElements())
   {
       list.insert(values go here);
    }

Answer 3

你的问题在这里：

                while ((line = br.readLine()) != null)
                {
                    // insert code to break input to pieces
                    StringTokenizer tokenizer = new StringTokenizer(line) ;
                    while (tokenizer.hasMoreElements())
                    {
                        Link record = new Link() ;
                        record.setBookName(tokenizer.nextToken()) ;
                        record.setBookAuthor(tokenizer.nextToken()) ;
                        record.setIsbn(tokenizer.nextToken()) ;
                        record.setPublicYear(tokenizer.nextToken()) ;
                    }
                    System.out.println (line) ;
                }

您正在为每条记录创建new Link()，填充它，从不将其添加到列表中。它打印原始数据，因为那里有System.out.println(line);。

Java程序：不使用方法打印

3 个答案: