读取带有数字的txt文件并将其保存在字符串矩阵中

Question

Im trying to read a txt file with numbers and saving each number in a String matrix but there some things i dont get.
1.-If i run the code in Eclipse i get printed like 16 times everything and the numbers get smaller and smaller..
2.-After beeing printed there is a null value on the bottom . why?
3.-Is it ok that the variable j is beeing defined outside the while loop? or should it be inside?

Thanks fot the help!

I wrote this so far: The text file is contains the following:

0000000000000000
0000000000000000
0000000400000000
0001111111160000
0001115111110000
0001161121510000
0001111511110000
0001110001110000
0000011311000000
0000011111000000
0000000000000000
0000000000000000
0000000000000000
0000000000000000
0000000000000000
0000000000000000

and the programm:

package Tests;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.LinkedList;

public class Test2 {

    public static void main(String [] args){

        try {
        File fil = new File("/Users/MaxRuizTagle/Desktop/AbschlussprojektWiSe1415/Canberra Fox - The Key Huntress/lvl/level0.txt");
        FileReader inputFil = new FileReader(fil);
        BufferedReader in = new BufferedReader(inputFil);

        String s = in.readLine();

        int largo = s.length();

        String [][] matrix = new String [largo][largo];

        String line;

        int j=0;

        while ((line=in.readLine() ) != null){
            for (int i=0;i<16;i++){
                matrix[i][j] = line.substring(i);   
            }
            j++;
        }

        for(int i=0;i<16;i++){
            for( j=0;j<16;j++){
                System.out.println(matrix[i][j]+" ");
            }
            System.out.println("");
        }


        }catch (IOException e1){
            e1.printStackTrace();

        }

    }

}

Answer 1

1) The reason that 16 blocks of numbers are printed is that you print 16 blocks of numbers here:

    for(int i=0;i<16;i++){
        for( j=0;j<16;j++){
            System.out.println(matrix[i][j]+" "); // <-- each one a line.
        }
        System.out.println("");
    }

The reason that they get shorter is that you previously saved ever shorter substrings here:

    for (int i=0;i<16;i++){
        matrix[i][j] = line.substring(i); // <-- substring from pos i to end
    }

You weren't very clear about your requirements, so I have to guess a little; it looks to me as though what you wanted to do was extract strings of one character each:

    for (int i=0;i<16;i++){
        matrix[i][j] = line.substring(i, i + 1); // substring from i to i + 1
    }

And later print each column in a line (transposing the image):

    for(int i=0;i<16;i++){
        for( j=0;j<16;j++){
            System.out.print(matrix[i][j]+" "); // print instead of println
        }
        System.out.println("");
    }

Although I wonder why you bother with an array of String s if you could use a char[][] matrix and line.charAt(i) or save the lines as they come and extract individual characters as lines[j].charAt(i) in the output loop.

2) You discard a line in the beginning:

    String s = in.readLine(); 

    int largo = s.length();

    // s is not used after this

because of this, your matrix shrinks from 16x16 to 15x16, and the loop

while ((line=in.readLine() ) != null){
  ...

doesn't initialize the last column of matrix , which remains filled with null s. The least invasive fix for that would be to, well, treat the first line in the loop like all others, as in

String line = s;

while(line != null) {
  ...

  line = in.readLine();
}

3) I see no problem with that.

4) The way you treat your array dimensions is a bit odd. You appear to read them from the file, but later they're hard-coded. If your code is only going to work with a 16x16 matrix, why do you bother with largo , and if it should work with matrices of other sizes, why is the size of 16 hardcoded everywhere else?

Answer 2

2.-After beeing printed there is a null value on the bottom . why?

Because the first line is not put in the matrix, you only use that for s.length() . Then the while loop will use only the 15 remaining lines, instead of 16. As a result, the last j index will have null values.

3.-Is it ok that the variable j is beeing defined outside the while loop? or should it be inside?

It's not great to be outside and reused. It's better to declare it inside.

Maybe you're looking for something more like this:

    for (int j = 0; j < 16; j++) {
        matrix[0][j] = String.valueOf(s.charAt(j));
    }
    for (int i = 1; (line = in.readLine()) != null; ++i) {
        for (int j = 0; j < 16; j++) {
            matrix[i][j] = String.valueOf(line.charAt(j));
        }
    }

    for (int i = 0; i < 16; i++) {
        for (int j = 0; j < 16; j++) {
            System.out.print(matrix[i][j] + " ");
        }
        System.out.println("");
    }