将文本文件读入二维数组

Question

I need to read a text file into a 2D array, I can read files into the program perfectly fine (see my code below) however I cannot get my head around how to read them into a 2D array. The array the function is reading into is a global array hence why it's not in the function.

Also I won't know the amount of rows the array has at first (currently set at 300 as it won't be over this) and I know this could cause a problem, I've seen some people suggest using ArrayLists however I have to have a 2D array so I was also wondering if there was a way to change an ArrayList to a 2D array and if this would be more effective?

 public static String readMaze(String fileName) {
        String line = null;

        try {
            FileReader fileReader = new FileReader(fileName);

            BufferedReader bufferedReader = new BufferedReader(fileReader);

            while ((line = bufferedReader.readLine()) != null) {
                System.out.println(line);

                for (int i = 0; i < mazeNew.length; i++) {

                    for (int j = 0; j < mazeNew[i].length; j++) {
                        // mazeNew[i][j] = ; - this is where I think something needs to be added
                    }
                }
            }

            bufferedReader.close();

        }

        catch (FileNotFoundException ex) {
            System.out.println("Unable to open file: " + fileName);
        }

        catch (IOException ex) {
            System.out.println("Error reading file: " + fileName);
        }

        return fileName;

    }

example text file:

11 4
5 6
4 6
0 5
3 5
8 7
1 4

Answer 1

There's a few options here, but generally you'll want to use the JavaScanner class as it's designed for exactly this kind of thing. Alternatively, use an existing structured data format (like JSON or XML) and an existing parser to go with it - the advantage being you can make use of a vast amount of tools and libraries which deal with those formats and don't have to re-invent anything.

However, following through with the scanner approach, it would be like so:

public static ArrayList<int[]> readMaze(String fileName) {

    // Number of ints per line:
    int width=2;

    // This will be the output - a list of rows, each with 'width' entries:
    ArrayList<int[]> results=new ArrayList<int[]>();

    String line = null;

    try {
        FileReader fileReader = new FileReader(fileName);

        BufferedReader bufferedReader = new BufferedReader(fileReader);

        Scanner mazeRunner = new Scanner(bufferedReader);

        // While we've got another line..
        while (mazeRunner.hasNextLine()) {

            // Setup current row:
            int[] row = new int[width];

            // For each number..
            for (int i = 0; i < width; i++) {

                // Read the number and add it to the current row:
                row[i] = mazeRunner.nextInt();

            }

            // Add the row to the results:
            results.add(row);

            // Go to the next line (optional, but helps deal with erroneous input files):
            if ( mazeRunner.hasNextLine() ) {

                // Go to the next line:
                mazeRunner.nextLine();

            }

        }

        mazeRunner.close();

    }

    catch (FileNotFoundException ex) {
        System.out.println("Unable to open file: " + fileName);
    }

    catch (IOException ex) {
        System.out.println("Error reading file: " + fileName);
    }

    return results;

}

Answer 2

If you have fixed no. of columns you can use this, but make sure input file must follow the same no of coulmns.

FileReader fileReader = new FileReader(fileName);

        Scanner sc = new Scanner(fileReader);
        int row=0, col=0;
        while ((sc.hasNext()) != null) {
            if(col < colSize){   //colSize is size of column
                mazeNew[row][col]= sc.nextInt();
            }
            else{
                col=0;
                row++;
            }
        }

Answer 3

Below is the core logic, you would probably also like to to handle some errors, such as how many elements is a line split into, are there empty lines, etc.

List<String[]> list = new ArrayList<>();
Pattern pattern = Pattern.compile("\\s+");
while ((line = bufferedReader.readLine()) != null) {
    list.add(pattern.split(line, -1));
}
String[][] mazeNew = list.toArray(new String[0][0]);

Answer 4

Something like this would work

it wont only read 2d text files .. it should work fine with any dimensions

public class Utile{
    public static ArrayList<int[]> readMaze(String path){
        ArrayList<int[]> result = new ArrayList<>();
        try{
            Scanner sc = new Scanner(new File(path));
            String[] temp;
            String line;
            while(sc.hasNextLine()){
                line = sc.nextLine();
                if (line.length() != 0){ //if the line is empty it will cause NumberFormatException
                    temp = line.split(" ");
                    int[] val = new int[temp.length];
                    for(int i = 0;i < temp.length;i++){
                        val[i] = Integer.pareseInt(temp[i]);
                    }
                    result.add(val);
                }
            }
            
            sc.close();
            
        }catch(Exception e){
            e.printStackTrace(); //just log it for now
        }
        return result;
    }
}

Answer 5

I am not a java expert, but in PHP I would do it with explode() . But I found an example how to do the same in java using string.split(). The result is the same ... an 2D Array of the content. If possible you should try to add an delimiter to the rows inside that text document. But you could split the rows on the space character either.

Example:

String foo = "This,that,other";
String[] split = foo.split(",");
StringBuilder sb = new StringBuilder();
for (int i = 0; i < split.length; i++) {
    sb.append(split[i]);
    if (i != split.length - 1) {
        sb.append(" ");
    }
}
String joined = sb.toString();