While defining a nested array you have to use a pair of square brackets [] for each level of nesting. And for "3d" array it would be [][][].

Note that there's actually no "2d" or "3d" array in Java. We can create a nested array, i.e. an array that contains other arrays.

While creating a nested array, only the length of the outer (enclosing) array needs to be provided. And you can omit declaring the sizes of the inner arrays, that can useful when inner arrays may differ in length.

I.e. this declaration will also be valid:

int[][][] loc = new int[5][][];

Another important thing about arrays that you need to be aware that although they are objects and inherit all behavior from the Object class, array don't have their own classes. As a consequence of this, if you invoke toString(), hasCode() and equals() on an array, a default implementation from the Object class would be invoked. Therefore, an attempt to print an array will result in strange symbols appearing on the console.

For that reason, Arrays utility class if your friend when need to print or compare arrays.

public static void main(String[] args) {

    int[][][] loc = new int[5][5][2];
    
    for (int row = 0; row < loc.length; row++) {
        for (int col = 0; col < loc[row].length; col++) {
            loc[row][col][0] = (1 + 2 * row) * 10;
            loc[row][col][1] = (1 + 2 * col) * 10;
        }
    }    

    print3DArray(loc);
}

public static void print3DArray(int[][][] arr) {
    for (int row = 0; row < arr.length; row++) {
        for (int col = 0; col < arr[row].length; col++) {
            System.out.print(Arrays.toString(arr[row][col]) + " ");
        }
        System.out.println();
    }
}

Output:

[10, 10] [10, 30] [10, 50] [10, 70] [10, 90] 
[30, 10] [30, 30] [30, 50] [30, 70] [30, 90] 
[50, 10] [50, 30] [50, 50] [50, 70] [50, 90] 
[70, 10] [70, 30] [70, 50] [70, 70] [70, 90] 
[90, 10] [90, 30] [90, 50] [90, 70] [90, 90]