How to read in a file of numbers into an array list in Java

Question

I want to be able to read in a map from a file that looks something like:

0, 0, 0, 0, 0

0, 0, 1, 0, 0

0, 1, 1, 1, 1

0, 1, 1, 1, 0

0, 0, 1, 1, 0

And create an array list that looks like:

{[0, 0, 0, 0, 0],

[0, 0, 1, 0, 0],

[0, 1, 1, 1, 1],

[0, 1, 1, 1, 0],

[0, 0, 1, 1, 0]}

I have tried using br.readLine() but it appears to be getting stuck but not throwing an error in the middle.

public static int[][] loadFile() throws IOException{

    FileReader in = new FileReader(Main.currentFilePath + Main.currentFile);
    BufferedReader br = new BufferedReader(in);
    String line;
    int [] intArray = {};
    int [][] fileArray = {};
    int j = 0;
    while ((line = br.readLine()) != null) {
        List<String> stringList = new ArrayList<String>(Arrays.asList(line.split(",")));
        String[] stringArray = stringList.toArray(new String[0]);
        List<Integer> intList = new ArrayList<Integer>();
        System.out.println("RRRRR");
        for(int i = 0; i < stringList.size(); i++) {
            Scanner scanner = new Scanner(stringArray[i]);
            System.out.println("GGGGG");
            while (scanner.hasNextInt()) {
                intList.add(scanner.nextInt());
                intArray = intList.parallelStream().mapToInt(Integer::intValue).toArray();
                System.out.println("FFFF");
            }
            System.out.println(fileArray[j][i]);
            fileArray[j][i] = intArray[i];
        }
        j++;
    }
    return fileArray;
    
}

It throws Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0 because your fileArray has a length of 0, it's impossible for you to add any new rows/columns to it — MadProgrammer
– MadProgrammer, Commented Apr 20, 2016 at 2:03
@HovercraftFullOfEels I think you misread it, I'm mysteriously getting no error, but the use of print statements tells me the program simply stops at fileArray[j][i] = intArray[i]; — cbbcbail
– cbbcbail, Commented Apr 20, 2016 at 2:05

MadProgrammer · Accepted Answer · 2016-04-20 02:09:54Z

The basic problem is, you're declaring an array of 0 length (no elements), which makes it impossible to add any elements to it.

int [][] fileArray = {};

Unless you know in advance EXACTLY the number of rows/columns you need, arrays are not very helpful, instead, you could make use of a List of some kind, for example...

List<int[]> rows = new ArrayList<>(5);
int maxCols = 0;
try (BufferedReader br = new BufferedReader(new FileReader(new File("Test.txt")))) {
    String text = null;
    while ((text = br.readLine()) != null) {
        System.out.println(text);
        String[] parts = text.split(",");
        int[] row = new int[parts.length];
        maxCols = Math.max(maxCols, row.length);
        for (int col = 0; col < parts.length; col++) {
            row[col] = Integer.parseInt(parts[col].trim());
        }
        rows.add(row);
    }
} catch (IOException ex) {
    ex.printStackTrace();
}

int[][] map = new int[rows.size()][maxCols];
for (int row = 0; row < rows.size(); row++) {
    map[row] = rows.get(row);
}

My "personal" gut feeling is simply not to bother with the arrays at all and simply make use of compound Lists...

List<List<Integer>> rows = new ArrayList<>(5);
try (BufferedReader br = new BufferedReader(new FileReader(new File("Test.txt")))) {
    String text = null;
    while ((text = br.readLine()) != null) {
        System.out.println(text);
        String[] parts = text.split(",");
        List<Integer> row = new ArrayList<>(parts.length);
        for (String value : parts) {
            row.add(Integer.parseInt(value.trim()));
        }
        rows.add(row);
    }
} catch (IOException ex) {
    ex.printStackTrace();
}

11thdimension · Accepted Answer · 2016-04-20 02:48:31Z

0

Here's the same with Java 8 magic

String filePath = "input.txt";
List<Integer[]> output = new ArrayList<>();

try(Stream<String> stream = Files.lines(Paths.get(filePath)) ) {

    stream.filter(line -> line != null && !line.isEmpty())
    .forEach(line->output.add(
        Arrays.stream(line.split(", "))//assuming that 2 numbers are separated by a comma followed by a white space
        .map(Integer::parseInt)
        .toArray(size -> new Integer[size])
    ));

} catch(Exception ex) {
    ex.printStackTrace();
}

output.forEach(s -> System.out.println(Arrays.toString(s)));

Output

[0, 0, 0, 0, 0]
[0, 0, 1, 0, 0]
[0, 1, 1, 1, 1]
[0, 1, 1, 1, 0]
[0, 0, 1, 1, 0]

answered Apr 20, 2016 at 2:48

11thdimension

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