Read data from a file into a 2D array

[sony vijay]

Hi,

Say, I have a file like so:

3
4
1,2,3,4
5,6,7,8
9,10,11,12

The first line represents the number of rows and the second line represents the number of columns. Thereafter, each line represents the data of a 2D array. I am using the following code to create a 2D array from the input file in Java.

import java.io.BufferedReader;
import java.io.FileReader;

/**
 * Creates a 2D matrix 
 */ 
public class CreateMatrix {
    private static BufferedReader in = null;
    private static int rows = 0;
    private static int columns = 0;
    private static int [][] matrix = null;
    public static void main(String []args) throws Exception {
        try {
            String filepath = args[0];
            int lineNum = 0;
            int row=0;
            in = new BufferedReader(new FileReader(filepath));
            String line = null;
            while((line=in.readLine()) !=null) {
                lineNum++;
                if(lineNum==1) {
                    rows = Integer.parseInt(line);
                } else if(lineNum==2) {
                    columns = Integer.parseInt(line);
                    matrix = new int[rows][columns];
                } else {
                    String [] tokens = line.split(",");
                    for (int j=0; j<tokens.length; j++) {
                        matrix[row][j] = Integer.parseInt(tokens[j]);
                    }
                    row++;
                }
            }
        } catch (Exception ex) {
            System.out.println("The code throws an exception");
            System.out.println(ex.getMessage());
        } finally {
            if (in!=null) in.close();
        }
    }
}

The above code works. But, my task is to modify the code in order to create a 2D array from the array data directly without having to specify the rows/columns in the input file. The input file would now look like so:
1,2,3,4
5,6,7,8
9,10,11,12

My code should be able to read this file and dynamically create a 3*4 array. I am not sure how to do that. Thank You!

[fred rosenberger]

One way or another, you're going to have to read the whole file first so you know how big your array has to be.

Whether you do multiple passes through it, store it all in memory, use some other data structure as an intermediary, or something else, you HAVE to know the dimensions of the array before you can declare it.

[Wendy Gibbons]

does it have to be an array, is there any reason you couldn't use an ArrayList?

[Joshi Nirav]

Hi all,

I think we can do it by this way.... This is a general Algorithm.

take some initial size of the No_Of_row = 2;
int oldData[] [] = null;
intialCounter = 0;
While(Read the File till EOF){
str := first line of the file.
col[] := split the 'str' by using the specific operator (In Our case its ',')
oldData = new int[No_Of_row][col.length];
initialCounter++;
if(initialCounter > No_Of_row){
int newData[][] = new int[initialCounter][col.length];
System.arrayCopy(oldata,0,newData,0,initialCounter - 1);
}else{
oldData[initialCounter - 1] = col;
}
}


Thanks and Regards
Nirav Joshi