Java question: How do I read a file into an double array; and then write it out to s

[Twyla]

Hi, I am doing this homework where I am suppose to read a .txt file fill with int number into a double array. After which I had to write this double array into another .txt file.
At first I though everything was working as I was able to read the file and display it out as an image, and then save it into a .txt file as double. However when I tried to use the same class file for another lesson (display it in frame I created), I keep getting 0.0 as the value of the output .txt file. Below is the code for my read and write class:

import java.io.*;
import java.util.*;
import java.awt.*;
import java.awt.event.*;
 
public class IO {
    FileDialog fd;
    public double[][] readData() { 
        fd = new FileDialog(new Frame(), "Open Files", FileDialog.LOAD);
        fd.setVisible(true);
        File f = null;
        if ((fd.getDirectory() != null)||( fd.getFile() != null)) {
            f = new File(fd.getDirectory() + fd.getFile());
        }
        FileReader fr = null;
        try {
            fr = new FileReader (f);
        } catch (FileNotFoundException fnfe) {
            fnfe.printStackTrace();
        }
        BufferedReader br = new BufferedReader(fr);
        int lines = -1;
        String textIn = " ";
        String[] file = null;
        try {
            while (textIn != null) {
                textIn = br.readLine();
                lines++;
            }
            file = new String[lines];
            fr = new FileReader (f);
            br = new BufferedReader(fr);
            for (int i = 0; i < lines; i++) {
                file[i] = br.readLine();
            }
            br.close();
        } catch (IOException ioe) {
            ioe.printStackTrace();
        }
        double[][] data = new double [lines][];
        for (int i = 0; i < lines; i++) {
            StringTokenizer st = new StringTokenizer(file[i],",");
            data[i] = new double[st.countTokens()];
            int j = 0;
            while (st.hasMoreTokens()) {
                data[i][j] = Double.parseDouble(st.nextToken());
                j++;
            }
        }
        return data;
    }
 
 
    public void writeData(double[][] dataIn) {
        fd = new FileDialog(new Frame(), "Save Files", FileDialog.SAVE);
        fd.setVisible(true);
        File f = null;
        if ((fd.getDirectory() != null)||( fd.getFile() != null)) {
            f = new File(fd.getDirectory() + fd.getFile());
        }
        FileWriter fw = null;
        try {
            fw = new FileWriter (f, true);
        } catch (IOException ioe) { 
            ioe.printStackTrace();
        }
        BufferedWriter bw = new BufferedWriter (fw);
        String tempStr = "";
        try {
            for (int i = 0; i < dataIn.length; i++) {
                for (int j = 0; j < dataIn[i].length; j++) {
                    tempStr = String.valueOf(dataIn[i][j]);
                    bw.write(tempStr);
                }
                bw.newLine();
            }
            bw.close();
        } catch (IOException ioe) {
            ioe.printStackTrace();
        }
    }
}
 

Any help will be greatly appreciated.