how to insert a new line character in a string to PrintStream then use a scanner to re-read the file

Question

I have several classes designed to simulation a book catalog. I have a book class (isbn, title, etc...), a BookNode class, a BookCatalog which is a LinkedList of books and a driver class (gui). My problem is that I have a toString() method in BookCatalog that supposed to return a String representation of all the books. The Book class also overrides toString(). I'm supposed to have each field of the book separated by a "tab" and each book separated by a "new line". When I try to use PrintStream to print the book catalog to a .txt file, the \n doesn't register.

I've tried to change it to System.getProperty(line.separator) which displays the bookcatalog correctly. But now, I have a problem where the Scanner will not read the file correctly and throws a "NoSuchElementException". How do I get the scanner to 1) Ignore the line.separator or 2) have printStream use \n?

Book.java

public String toString(){
        return isbn+"\t"+lastName+"\t"+firstName+"\t"+title+"\t"+year+"\t"+
            String.format("%.2f",price);

BookCatalog.java

public String toString() {
        BookNode current = front;
        String s="";
        System.out.println(s);
        while (current!=null){
            //each book is listed on separate line
            s+=current.getData().toString()+"\n ";//System.getProperty("line.separator")
            current = current.getNext();
        }
        return s;
    }

Driver.java

public void loadDirectory() throws FileNotFoundException {
        if (f.exists()){
            Scanner input = new Scanner(f);
            while (input.hasNextLine()){
                String bookLine = input.nextLine();
                processBookLine(bookLine);
            }
        }
    }

public void processBookLine(String line){
        Scanner input = new Scanner(line);
        String isbn = input.next();
        String lastName = input.next();
        String firstName = input.next();

        String title = input.next();
        while (input.hasNext() && !input.hasNextInt()){//while next token is not an integer
            title += " "+input.next();
        }
        int year = input.nextInt();
        double price = input.nextDouble();
        Book book = Book.createBook(isbn, lastName, firstName, title, year, price);
        if (book!=null){
            catalog.add(book);
        }
    }

If you're claiming that `PrintStream` suppresses the `\r` you are mistaken. The remainder of your question is not clear. — user207421, Mar 19 '13 at 23:30
I used the System.getProperty("line.separator") instead of \n so when i open the newly created file (from PrintStream) and tried to reread it (scanner), it will not process the line. I'm assuming that the "line.separator" is the reason why so I tried to save the character in another variable to bypass it but that didn't work either. — Sara, Mar 20 '13 at 20:38

score 31 · Accepted Answer · edited Mar 22 '13 at 05:02

31

The linefeed character \n is not the line separator in certain operating systems (such as windows, where it's "\r\n") - my suggestion is that you use \r\n instead, then it'll both see the line-break with only \n and \r\n, I've never had any problems using it.

Also, you should look into using a StringBuilder instead of concatenating the String in the while-loop at BookCatalog.toString(), it is a lot more effective. For instance:

public String toString() {
        BookNode current = front;
        StringBuilder sb = new StringBuilder();
        while (current!=null){
            sb.append(current.getData().toString()+"\r\n ");
            current = current.getNext();
        }
        return sb.toString();
}

edited Mar 22 '13 at 05:02

user207421

305,947
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answered Mar 19 '13 at 23:29

ddmps

4,350
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I don't see any reason why this should make any difference. Scanner handles \n, \r, and \r\n as line terminators already, and several others as well. – user207421 Mar 22 '13 at 05:07
@EJP Scanner yes, but if you open a .txt on notepad with only \n in Windows, it will not register. – ddmps Mar 30 '14 at 00:15
@ddmps It inserts an extra line at the end! Please suggest how to handle it! – AVA Oct 15 '15 at 09:38
2

@AVA I do not see the issue with the "extra" line. See http://stackoverflow.com/a/729795/1690982. – ddmps Oct 15 '15 at 19:18
@ddmps Thanks for clarification with reference! – AVA Oct 26 '15 at 07:49
Using "\r\n" instead of "\n" work just fine for me. Thanks alot. Upped!. – iamjoshua Jan 15 '18 at 16:32

how to insert a new line character in a string to PrintStream then use a scanner to re-read the file

1 Answers1