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

Sara picture Sara · Mar 20, 2013 · Viewed 182.7k times · Source

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);
        }
    }

Answer

ddmps picture ddmps · Mar 20, 2013

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();
}