Write Array to File

Question

I am trying to do an exercise in the book that asks to write the contents of the array list to a text file, can someone give me some ideas on what I am doing wrong opposed to full solutions, do I need to make a method that returns a single string then write that?

import java.util.ArrayList;
import java.io.FileWriter;
import java.util.Iterator;

/**
 * A class to maintain an arbitrarily long list of notes.
 * Notes are numbered for external reference by a human user.
 * In this version, note numbers start at 0.
 * 
 * @author David J. Barnes and Michael Kolling.
 * @version 2008.03.30
 */
public class Notebook {
    // Storage for an arbitrary number of notes.
    private ArrayList<String> notes;

    /**
     * Perform any initialization that is required for the
     * notebook.
     */
    public Notebook() {
        notes = new ArrayList<String>();
    }

    /**
     * Store a new note into the notebook.
     * @param note The note to be stored.
     */
    public void storeNote(String note) {
        notes.add(note);
    }

    /**
     * @return The number of notes currently in the notebook.
     */
    public int numberOfNotes() {
        return notes.size();
    }

    /**
     * Remove a note from the notebook if it exists.
     * @param noteNumber The number of the note to be removed.
     */
    public void removeNote(int noteNumber) {
        if(noteNumber < 0) {
            // This is not a valid note number, so do nothing.
        } else if(noteNumber < numberOfNotes()) {
            // This is a valid note number.
            notes.remove(noteNumber);
        } else {
            // This is not a valid note number, so do nothing.
        }
    }

    /**
     * List all notes in the notebook.
     */
    public void listNotes() {
        for(String note : notes) {
            System.out.println(note);
        }
    }

    /**
     * 
     */
    public void writeToFile() {
        try{
            FileWriter writer = new FileWriter("file.txt");

            for(String str : notes){
                writer.write(str.toString());
            }
        }
        catch(Exception e ){
            System.out.println("some error...");
        }
    }
}

edit: the problem I am having now is that I can't get each string on a new line even if I use the writer.write('\n'), I realized I forgot the writer.close(); ;)

What happens when you create a Notebook, add some notes to it, then call your writeToFile() method? — Bill the Lizard
– Bill the Lizard, Commented Mar 29, 2009 at 15:44
nothing happened until i realised i missed out writer.close after the loop :p the problem i am having now is that i cant get each string on a new line even if i use the writer.write('\n') — Simion
– Simion, Commented Mar 29, 2009 at 15:53
Don't forget that depending on your platform, you may need a carriage return and/or a line feed.... — Brian Agnew
– Brian Agnew, Commented Mar 29, 2009 at 16:57

Maurice Perry · Accepted Answer · 2009-03-29 15:46:41Z

2

Things that look wrong to me:

calling toString() on a string is pure waste
the writer is never closed
notes are written in the file without any separator between them. The file might be hard to read.

answered Mar 29, 2009 at 15:46

Maurice Perry

32.8k9 gold badges72 silver badges97 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Brian Agnew · Accepted Answer · 2009-03-29 16:55:26Z

1

You want to have a look at closing the FileWriter on completion. Otherwise, what forces the FileWriter to complete its operation ?

edited Mar 29, 2009 at 16:55

answered Mar 29, 2009 at 15:42

Brian Agnew

273k38 gold badges342 silver badges443 bronze badges

Comments

dsr · Accepted Answer · 2009-03-29 17:18:35Z

1

Get the system newline property in a string variable.

String newline = System.getProperty("line.separator");

Then in the file write module append newline to the end of each line.

writer.write(str.toString() + newline);

edited Mar 29, 2009 at 17:18

answered Mar 29, 2009 at 17:02

dsr

1,3162 gold badges14 silver badges22 bronze badges

Comments

TofuBeer · Accepted Answer · 2009-03-29 20:13:47Z

1

Without altering your code very much...

try{
    PrintWriter writer = new PrintWriter(new FileWriter("file.txt"));

    for(String str : notes){
        writer.println(str.toString());
    }

answered Mar 29, 2009 at 20:13

TofuBeer

61.6k18 gold badges120 silver badges163 bronze badges

Comments

Paul Tomblin · Accepted Answer · 2009-03-29 15:48:29Z

0

You don't have any way to delimit the strings, so when you read them back in, you won't know where one string ends and the next begins. Since Java Strings are Unicode, there are very few things you could write to the file that would not legitimately be in your strings. So what I would recommend doing is to write an int representing the length of the string, and then the string so you know how much to read. Conversely, you could look into using Java's serialization methods and just serialize the whole List into a file.

But then again, I'm a database guy, and am most comfortable with PreparedStatements and ResultSets, so I'd probably just do it all as an SQLite database.

answered Mar 29, 2009 at 15:48

Paul Tomblin

184k59 gold badges324 silver badges412 bronze badges

Collectives™ on Stack Overflow

Write Array to File

5 Answers 5

Comments

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

Comments

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related