Practice with a simple file

Take baby steps. First, be sure you are opening a file successfully.

Modern Java offers the Path, File, and Files classes to make handling files on storage much easier.

Example:

package work.basil.example;

import java.io.BufferedWriter;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class Csver
{
    public static void main ( String[] args )
    {
        Csver app = new Csver() ;
        app.writeDummyFile() ;
    }

    private void writeDummyFile ()
    {
        Path path = Paths.get( "/Users/basilbourque/dummy.txt" ) ;
        // Use try-with-resources to auto-close the file if successfully opened.
        try ( 
            BufferedWriter writer = Files.newBufferedWriter( path ) ;  // Will be automatically closed if successfully opened.
        )
        {
            writer.write( "Bonjour le monde!" ) ;
        } catch ( IOException e )
        {
            e.printStackTrace() ;
        }
    }

}

Use a library for CSV

Next, for CSV or Tab-delimited files or such, use a library. I use Apache Commons CSV. Search Stack Overflow for many examples of using this and other such libraries to read and write these kinds of files.

Use CSVFormat to define the type of file. Here we use standard CSV as defined by RFC 4180. Note that standard CSV uses CRLF (CARRIAGE RETURN LINE FEED) to denote line breaks rather then LF (LINE FEED) seen commonly in Unix-like platforms.

When opening the file, we specify UTF-8 character encoding. UTF-8 is generally the best encoding to use; it covers all the Unicode characters, and is a superset of US-ASCII.

The CSVPrinter::print method adds a field at a time when outputting a row. We terminate the row by calling CSVPrinter::println.

I renamed your i & j variables to be meaningful.

I added column names at the top of the file. You may want to keep or discard that feature, up to you.

Notice how we are using try-with-resources syntax to auto-close our file.

package work.basil.example;

import org.apache.commons.csv.CSVFormat;
import org.apache.commons.csv.CSVPrinter;
import org.apache.commons.csv.CSVRecord;

import javax.swing.*;
import javax.swing.table.TableModel;
import java.io.BufferedWriter;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class Csver
{
    public static void main ( String[] args )
    {
        Csver app = new Csver();

        // Practice writing a simple file.
        app.writeDummyFile();

        // Write out the data in a JTable to standard CSV file.
        JTable jtable = app.newJTable();
        app.writeCSV( jtable.getModel() );

        System.out.println( "« fin »" );
    }

    private void writeCSV ( final TableModel model )
    {
        CSVFormat format = CSVFormat.RFC4180;
        Path path = Paths.get( "/Users/basilbourque/animals.csv" );
        try (
                BufferedWriter writer = Files.newBufferedWriter( path , StandardCharsets.UTF_8 ) ;
                CSVPrinter printer = new CSVPrinter( writer , format ) ;
        )
        {
            // Print column headers, if you want.
            for ( int columnIndex = 0 ; columnIndex < model.getColumnCount() ; columnIndex++ )
            {
                printer.print( model.getColumnName( columnIndex ) );
            }
            printer.println();

            // Print rows.
            for ( int rowIndex = 0 ; rowIndex < model.getRowCount() ; rowIndex++ )
            {
                for ( int columnIndex = 0 ; columnIndex < model.getColumnCount() ; columnIndex++ )
                {
                    printer.print( model.getValueAt( rowIndex , columnIndex ) );
                }
                printer.println();
            }
        } catch ( IOException e )
        {
            e.printStackTrace();
        }
    }

    private JTable newJTable ()
    {
        String[] columnNames = { "Species" , "Name" };
        Object[][] data = {
                { "Dog" , "Delilah" } ,
                { "Cat" , "René" } ,
                { "Bird" , "Jordan" }
        };
        JTable table = new JTable( data , columnNames );
        return table;
    }

    private void writeDummyFile ()
    {
        Path path = Paths.get( "/Users/basilbourque/dummy.txt" );
        // Use try-with-resources to auto-close the file if successfully opened.
        try ( BufferedWriter writer = Files.newBufferedWriter( path ) )
        {
            writer.write( "Bonjour le monde!" );
        } catch ( IOException e )
        {
            e.printStackTrace();
        }
    }

}

Make sure you call csv.flush() before closing the file. :)