How would I make an entire row in an array one value in Java?

Question

How would I make an entire row (or column) one value in an array? For example, I have a row of all random numbers, and I want to set all of these values to 0.

Here is what I have so far:

public class Assignment12 {
    public static void main(String args[]) {
        int[][] timestable = new int[10][10];
        printSquare(timestable);
        zeroRow(timestable, 5);
        printSquare(timestable);
        int[] arr = timestable[0];
    }

    public static void printSquare(int[][] arr) {
        for (int row = 0; row < 10; row++)
            for (int col = 0; col < 10; col++)
                arr[row][col] = (row + 1) * (col + 1);

        System.out.println();
        for (int row = 0; row < 10; row++) {
            for (int col = 0; col < arr.length; col++)
                System.out.printf("%4d", arr[row][col]);
            System.out.println();
        }
    }

    public static void zeroRow(int[][] arr, int M) {
        for (int col = 0; col < M; col++) {
            if (arr[M][col] != 0) {
                arr[M][col] = 0;
            }
        }
    }
}

Answer 1

1. Arrays of primitives are filled with default values ( 0 for integer types, 0.0 / 0.0f for floating-point types, false for boolean ) and null for objects upon creation .

2. To populate a single row in a 2D array, it's recommended to use Arrays.fill method:

public static void fillRow(int[][] arr, int row, int value) {
    if (row < arr.length && row >= 0 && null != arr[row]) {
        Arrays.fill(arr[row], value);
    }
}

public static void zeroRow(int[][] arr, int row) {
    fillRow(arr, row, 0);
}

3. Specific columns can be filled using loops:

public static void fillColumn(int[][] arr, int col, int value) {
    for (int[] row : arr) {
        if (null != row && col >= 0 && col < row.length) {
            row[col] = value;
        } 
    }
}

public static void zeroColumn(int[][] arr, int col) {
    fillColumn(arr, col, 0);
}

Answer 2

How would I make an entire row in an array one value in Java?

By default, primitive int arrays of a fixed length are initialized to 0's. To fill them with other values you can do the following.

Use the Arrays.fill method.

int[] tens = new int[5];
Arrays.fill(tens,10);

System.out.println(Arrays.toString(tens));

Prints

[10, 10, 10, 10, 10]

Or you can write a lambda and call it when you need to fill an array. It will also create the array for you since you supply the length.

BiFunction<Integer, Integer, int[]> fill =
        (val, len) -> {
                  int[] temp = new int[len];
                  Arrays.fill(temp, val);
                  return temp;};
        
int[] twos = fill.apply(2,10);
int[] threes = fill.apply(3,4);

System.out.println(Arrays.toString(twos));
System.out.println(Arrays.toString(threes));

prints

[2, 2, 2, 2, 2, 2, 2, 2, 2, 2]
[3, 3, 3, 3]

Or, in a pinch, generate one from an IntStream . For an array of 5's with length of 7 do the following:

int[] fives = IntStream.generate(()-> 5).limit(7).toArray();

Note: Once you have your linear array you can also assign it to any row in a 2D array. Consider the previous examples of twos and threes .

int[][] b = new int[2][];
b[0] = twos;
b[1] = threes;

Answer 3

You can process an array as follows:

public static void fillRow(int[][] arr, int row, int val) {
    Arrays.fill(arr[row], val);
}

public static void fillColumn(int[][] arr, int column, int val) {
    Arrays.stream(arr).forEach(row -> row[column] = val);
}

public static void main(String[] args) {
    int[][] arr = new int[5][5];
    fillRow(arr, 3, 3);
    fillColumn(arr, 2, 2);

    // output
    Arrays.stream(arr).map(Arrays::toString).forEach(System.out::println);
}

---

[0, 0, 2, 0, 0]
[0, 0, 2, 0, 0]
[0, 0, 2, 0, 0]
[3, 3, 2, 3, 3]
[0, 0, 2, 0, 0]