Reading a 2d array from a file in java

Question

I have a text file that is 32x32 in size. For example first two lines:

11111111111111111111111111111111
11111111111111111111111111111000
...

I want to read and store this file in a 2D array. I have the following java code, but can't exactly figure out how to read the file data. I guess I would need two nested for loops?

public static int[][] readFile(){
BufferedReader br = null;
int[][] matrix = new int[32][32];
try {

    String thisLine;
    int count = 0;


    br = new BufferedReader(new FileReader("C:\\input.txt"));

    while ((thisLine = br.readLine()) != null) {

    //two nested for loops here? not sure how to actually read the data

    count++;
    }
    return matrix;                      


} 
catch (IOException e) {
    e.printStackTrace();
} 
finally {
    try {
        if (br != null)br.close();
        } 
    catch (IOException ex) 
        {
        ex.printStackTrace();
        }
}
return matrix;
}

That's simple : how do you convert a String of digits into an array of integers ? — Dici
– Dici, Commented Sep 25, 2014 at 17:53

Barranka · Accepted Answer · 2014-09-25 17:56:36Z

3

Assuming that each line in your file is a row, and, for each row, a character is an entry:

// ...
int i,j;
i = 0;
while((thisLine = br.readLine()) != null) {
    for(j = 0; j < thisLine.lenght(); j++) {
        matrix[i][j] = Character.getNumericValue(thisLine.charAt(j));
    }
    i++;
}
// ...

This is just a starting point... there may be many more efficient and clean ways to do this, but now you have the idea.

answered Sep 25, 2014 at 17:56

Barranka

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Comments

Mshnik · Accepted Answer · 2014-09-25 17:57:42Z

1

You only need one more loop, since the while loop you already have is functioning as the outer loop.

while ((thisLine = br.readLine()) != null) {
    for(int i = 0; i < thisLine.length(); i++){
        matrix[count][i] = Character.getNumericValue(thisLine.charAt(i));;
    }

count++;
}

answered Sep 25, 2014 at 17:57

Mshnik

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2 Comments

Barranka Over a year ago

Identical to my answer ;)

user3247171 Over a year ago

Got it thanks... And to write the 2D array back to file I just change it from BufferedReader to BufferedWriter?

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