Question

I’m using BufferedReader to read a .csv file. I have no problem reading the file and extracting the data. However, the problem that I do have is that I have to hard-code my array declaration. For example:

        String[][] numbers=new String[5258][16];

The .csv file I was using had 5258 rows and 16 columns. I’d like to be able to do something like this though:

        String[][] numbers=new String[rowsInFile][16];

In other words, I want the variable ‘rowsInFile’ to be equivalent to the amount of rows in the file (I don’t want to count the columns, because every .csv file I will be running through this program has 16 columns).

Here’s the code I have so far:

        int row = 0;
        int col = 0;

        String fileInput = JOptionPane.showInputDialog(null, 
                "Please enter the path of the CSV file to read:");

        File file = new File(fileInput);

        BufferedReader bufRdr;
        bufRdr = new BufferedReader(new FileReader(file));
        String line = null;

        //get rows in the file
        int rowsInFile = 0;
        while(bufRdr.readLine() != null) {
            rowsInFile++;
            row++;
        }
        String[][] numbers=new String[rowsInFile][16];

        //read each line of text file
        row = 0;
        while((line = bufRdr.readLine()) != null) {
            StringTokenizer st = new StringTokenizer(line,",");
            col=0;

            while (st.hasMoreTokens()) {
                //get next token and store it in the array
                numbers[row][col] = st.nextToken();
                col++;
            }
            row++;
        }

However, I’m getting a null pointer exception. Any ideas of what I should do?

P.S. Yes, this code is surrounded by a try/catch statement.

Answer 1

The problem is, once you go through the BufferedReader once, you can’t go back through it again. In other words, you have to use a new BufferedReader.

bufRdr = new BufferedReader(new FileReader(file));
row = 0;
while((line = bufRdr.readLine()) != null) {

Alternatively, you could use a dynamic array structure like an ArrayList<String[]> or a LinkedList<String[]> to store the rows.

LinkedList<String[]> numbers = new LinkedList<String[]>();

while( (line = bufRdr.readLine()) != null ) {
    numbers.add(line.split(","));
}

Then instead of doing numbers[i][j], you use numbers.get(i)[j].