Replacing rows and columns in a 2d array

Question

I have a 2d array :

1 0 1 1
1 1 1 1
1 1 1 1
1 1 1 1

I have to write a program that checks if there is a 0 in the array and if so replace the row and column with 0's so it looks like this after :

0 0 0 0
1 0 1 1
1 0 1 1
1 0 1 1

This is my code so far :

public class Run {


    public static void main(String[] args){
        //defining 2d array
        int[][] m = { {1,0,1,1}, 
                      {1,1,1,1},
                      {1,1,1,1},
                      {1,1,1,1}}; 
        int[][] newArray = zero(m);
        //looping through the array to get rows and columns for the array
        //rows
        for (int i = 0; i < m.length; i++) {
            //columns
            for (int j = 0; j < m[0].length; j++) { 
                //check if the integer is the last in the row
                if(j== m.length-1){
                    //print the rows and columns of the array(no space)
                    System.out.print(newArray[i][j]);
                }else{
                    //print the rows and columns of the array(w/ space)
                    System.out.print(newArray[i][j] + " ");
                }
            }
            //new line for the new row
        System.out.println("");
        }
    }

    //checks if there is a zero in the row
    public static int[][] zero(int[][] m) {
        //defining row length and column length
        int rows = m.length;
        int columns = m[0].length;
        int[][] tempArray = m;

        //looping through the array to get rows and columns
        //rows
        for (int i = 0; i < rows; i++) {
            //columns
            for (int j = 0; j < columns; j++) {
                //if the number is 0 loop through that row and column again and change everything to 0 
                if(m[i][j] == 0){
                    //columns in that row
                    for(int l = 0; l < rows; l++)
                    {
                        tempArray[l][j] = 0;
                    }
                    //rows in that column
                    for(int l = 0; l < columns; l++)
                    {
                        tempArray[i][l] = 0;
                    }
                }
            }
        }

        //returning the updated array
        return tempArray;
}

}

when I run my code it returns :

0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0

but when I take out either :

    //columns in that row
for(int l = 0; l < rows; l++)
{
    tempArray[l][j] = 0;
}

or

    //rows in that column
for(int l = 0; l < rows; l++)
{
    tempArray[l][j] = 0;
}

it returns :

0 0 0 0
1 1 1 1
1 1 1 1
1 1 1 1

or

1 0 1 1
1 0 1 1
1 0 1 1
1 0 1 1

Answer 1

You detect 0 in a loop, then go and modify the data and continue your loop which is now going to see more zeros and so set even more zeros.

You should either break once you've spotted a 0, or split the detection and "rewriting" - do all the detection first then all of the rewriting.

Answer 2

The problem is the line

int[][] tempArray = m;

This makes tempArray and m the exact same instance, so you only actually have one matrix.

Instead you should do

int[][] tempArray = new int[rows][columns];
for (int i = 0; i < rows; i++)
    for (int j = 0; j < columns; j++)
        tempArray[i][j] = m[i][j];