populate array from txt file

[Kory Perry]

I'm looking to populate a multidimensional array with integers that are read from a txt file by using a method.
For example my array looks like this:    

public static void gameBoard(int[][] M) throws Exception{

}

and my txt file has these numbers with a space between each integer:
0 1
1 1
2 4
3 4
4 4
5 3
5 5
5 6
6 1
6 2
6 4
6 6
7 5
7 7

How would I get these numbers into the arrays?  I've tried using a while loop and hasNext() to read the txt file but I havn't been able to successfully populate the array with anything.  Any advice?

[Paul Clapham]

Before you start writing code to "get these numbers into the arrays" you need to find out what that means. (Writing code for requirements that you don't understand is a bad idea.)

Now, maybe you know what that means already. But I sure don't. Your code fragment implies you have a two-dimensional array, although we have no idea how big it is. And there are 24 integers in the input that you posted; are they supposed to go into the array? If so, what are the rules for putting them in? Or is there something else going on with those numbers?

[Kory Perry]

The integers that I showed are the row and column points in the txt file that have read into my game board.

Here is what I have written so far:

static final int SIZE = 8;

    public static void main(String[] args) throws Exception {

        int[][] board = new int[SIZE][SIZE];
        initBoard(board);


        System.out.println("Game board:\n");
        printBoard(board);
    }

    
    // this will initialize board locations to a 1.
    public static void initBoard(int[][] M) throws Exception {

        File myFile = new File("game.txt");
        Scanner sc = new Scanner(myFile);


    }

    
    public static void printBoard(int[][] M) {
        for (int r = 0; r < SIZE; r++) {
            for (int c = 0; c < SIZE; c++) {
                if (M[r][c] == 1)
                    System.out.print("    *");
                else
                    System.out.print("    .");

            }
            System.out.println();
        }
        System.out.println("\n");
    }

My int [][]initBoard method is where I am having difficulty.  I've tried using hasNext() to read the txt file but my board isnt printing the integers into the row and columns.

[Carey Brown]

"hasNext()" doesn't read the next token, it just returns true if there is one to read. To actually read it you need "next()".

I think you want to read ints though, so use "hasNextInt()" and "nextInt()".

If your file has a row that says
5 6

Does that mean you want to
array[ 5 ][ 6 ] = 1; // ???

[fred rosenberger]

Kory Perry wrote:I'm looking to populate a multidimensional array with integers that are read from a txt file by using a method.

This is more complicated than you make it sound.  it's not one thing, it's many.
1) You need to populate many arrays with integers you get from <somewhere>.
2) you need to populate an array of arrays of integers you get from <somewhere>
3) You need to read from a file
4) you need to parse data from that file
5) you need to validate the data in the file (maybe...it depends on how sure you are your file will only contain ints)

There may even be more steps.  But each of the above could really be a method in and of itself.

One of the hardest things to learn is that a method shouldn't do too much.  It's much better, safer, and easier to write a lot of small methods that each do one thing, and do it well, than to write a single, monolithic method that tries to do everything.  It also makes you program more flexible.  If your method that builds the array doesn't have any logic about getting the data, you can change it later...maybe you'll want to read from a database, or a port on a remote server...if the method for getting the data is completely separate from the method that uses the data, you can change one (or even replace it entirely) without worrying about the other.

[Carey Brown]

Fred, I mostly agree with you except for your step (1). I don't see where you get that from.

[fred rosenberger]

Carey Brown wrote:Fred, I mostly agree with you except for your step (1). I don't see where you get that from.

Java does not have 2-d arrays.  you have an array that holds arrays.  the OP needs to build many small int arrays, that then get put into the int [][].

[Carey Brown]

OP did this with

int[][] board = new int[SIZE][SIZE];

Though  elements are not initialized to zero which would have happened if it was declared as a member variable.
EDIT: I was wrong. Even declared as local variable they are initialized to zero.

[Carey Brown]

Kory, you've got a start there. One change needed right off is to use try-with-resources to open the Scanner. In that way the Scanner will be automatically closed before the method returns.

    public static void initBoard(int[][] M) throws Exception {
 
        File myFile = new File("game.txt");
        try( Scanner sc = new Scanner(myFile) )
        {
             while( true )
             {
                 // if you don't have hasNextInt() then you are done
                 // reading the file and can return

                 // read row
                 // read col
                 M[row][col] = 1;
             }
        }
    }

Also, variable names should begin with a lower case letter.

[Campbell Ritchie]

I think you will have to use while (myScanner.hasNextInt()) ... or similar, otherwise you will suffer an exception when you overrun the end of the file.

[salvin francis]

I have a slightly different thought process here...

Does the 1 say that the board cell is occupied ?
What's the use of having a large array of 0s and having only some of them as 1 ?

I would imagine a simple array like this:

List<BoardPiece> occupiedList = ...

where BoardPiece can be:

class BoardPiece{
  int row, column;
  ...
}

If there is more than one "state" .. you may want to think about an enum here.

[Kory Perry]

My post was just a smaller version of what I actually have below.  I was just trying to see if I could get that text file into the arrays and then use that logic with my final code.  The integers in the text file are just coordinates that need to be displayed as *s on the grid.  The M[][] arrays that I have commented out were just coordinate tests to see if everything works.  Since they do work, I'm trying to replace them with the integers in my txt file instead.  I've been scratching my brain for days trying to figure out how to read that text file into the grid and display the *s.  Hopefully that makes more sense to the people that have been trying to help.

import java.util.*;
import java.io.*;

public class MultiGameFile {
    static final int SIZE = 8;

    public static void main (String [] args) throws Exception {


        boolean playAgain = true;
        Scanner sc = new Scanner(System.in);

        int numGen = 0;
        int [][] board = new int [SIZE][SIZE];
        int [][] nextBoard = new int [SIZE][SIZE];
        initBoard(board);

        System.out.println("Here's the initial board:\n");
        printBoard(board);

        do {
            // count Generation and print
            numGen++;
            System.out.println("Generation # " + numGen);

            for(int r = 1; r <= SIZE - 2; r++){
                for(int c = 1; c <= SIZE-2; c++){

                    int neighbors = numNeigh(board,r,c);
                    nextBoard[r][c] = 0;

                    if(board[r][c]==1){
                        if(neighbors == 2 || neighbors ==3){
                            nextBoard[r][c] = 1;
                        }
                    }
                    else{
                        if(neighbors ==3){
                            nextBoard[r][c] = 1;
                        }
                    }
                }
            }

            copyFromNextBoard(board, nextBoard);
            printBoard(board);
        } while (playAgain());

        System.out.println("Game over.");

    }
    
    
    public static int numNeigh(int[][] M, int r, int c) {
        // this should return the number of neighbors.
        int total = M[r-1][c-1] + M[r-1][c] + M[r-1][c+1];
            total+= M[r][c-1]               + M[r][c+1];
            total+= M[r+1][c-1] + M[r+1][c] + M[r+1][c+1];
            return total;
    }

    // this will initialize board locations to a 1.
    public static void initBoard(int[][] M) throws Exception {


        File myFile = new File("game.txt");
        Scanner sc = new Scanner(myFile);


        int numbers = 0;
        while(sc.hasNextInt() ){
            numbers = sc.nextInt();  // reading the txt file


        }
    }

//        M[0][2] = M[1][1] = M[1][2] = M[2][3] = M[1][5] =
//                M[4][4] = M[4][5] = M[5][4] = M[5][5] = M[5][6] =
//                        M[6][6] = M[6][7] = M[7][6] = M[7][4] = 1;


    public static void copyFromNextBoard(int [][] board, int [][] nextBoard) {

        for(int r = 1; r <SIZE - 1; r++) {
            for (int c = 1; c <SIZE - 1; c++) {
                board[r][c] = nextBoard[r][c];
            }
        }
    }


    public static void printBoard(int [][] M) {
        for (int r=0; r<SIZE; r++) {
            for (int c=0; c<SIZE; c++) {
                if (M[r][c] == 1)
                    System.out.print("    *");
                else
                    System.out.print("    .");

            }
            System.out.println();
        }
        System.out.println("\n");
    }

    public static boolean playAgain() {
        Scanner sc = new Scanner (System.in);
        char c;
        System.out.print("Keep playing?  (y or n): " );
        c = sc.next().charAt(0);
        if (c == 'y' || c == 'Y') {
            return true;
        }
        return false;

    }
}

[Campbell Ritchie]

I suggest you start by removing the keyword static everywhere except the main() method and constant declarations. Things static do have their place, but that place is the exception not the rule.
Don't call variables anything like M. It isn't clear what that means, and anyway, only constants should have upper‑case names. Don't put spaces before the [] in array types: int[][] please not int [][].
Don't write if (something) return true; else return false;
Write return c == 'y' || c == 'Y';

As Salvin says, why are you using numbers when you mean a cell is occupied or vacant?
Please provide some explanation of your algorithms; how are you counting neighbours to a square?
Please tell us what problems you are suffering.

[Kory Perry]

After tinkering around with my while loop, I was able to get everything working.  Thanks everyone for all the help.

[Campbell Ritchie]

Please show us what you have got.

[Kory Perry]

First I changed my variables like suggested.  Then I called the coordinates and set my rows and columns to 1.

    // this will initialize board locations to a 1.
    public static void initBoard(int[][] coordinates) throws Exception {


        File myFile = new File("game.txt");
        Scanner sc = new Scanner(myFile);

//        M[0][2] = M[1][1] = M[1][2] = M[2][3] = M[1][5] =
//                M[4][4] = M[4][5] = M[5][4] = M[5][5] = M[5][6] =
//                        M[6][6] = M[6][7] = M[7][6] = M[7][4] = 1;

       int rows = sc.nextInt();
        int columns = sc.nextInt();

        int [][] matrix =  new int [rows][columns];

        while(sc.hasNextInt() ){
            int row = sc.nextInt();
            int col = sc.nextInt();

            coordinates[row][col] = 1;
        }

    }

Here's the game board after the txt file has been read into the grid.

[Campbell Ritchie]

Not bad
You still have everything static, which I told you yesterday isn't correct.
You are neither opening nor closing your Scanner correctly. Look at the Java™ Tutorials and also find the basic IO section. This is how it should be done:-

try (Scanner fileScan = new Scanner(Paths.get("myFile")))
{
   while (fileScan.hasNext())
   {
      something(fileScan.nextInt());
   }
}
catch (IOException ex)
{
   // ...
}

Use a Path rather than a File object. Don't write close();. You may prefer to rethrow the exception and handle it elsewhere. If so, write a throws instead of a catch.

[Campbell Ritchie]

To continue from what Salvin said earlier, why are you using numbers and printing them as *s? Why not use an enum?