Determine the Upper Bound of a Two Dimensional Array in Java

Multidimensional arrays in Java are common and can be termed as an array of arrays. Data in a two-dimensional array in Java is stored in 2D tabular form. A two-dimensional array is the simplest form of a multidimensional array. A two-dimensional array can be seen as an array of the one-dimensional array for easier understanding. A two-dimensional array is declared with two dimensions that are also referred to as their bounds. 

Syntax of an Array of Arrays:

data_type[][] array_name = new data_type[x][y];

For example: int[][] arr = new int[20][30];    // 20 X 30 array of arrays

Direct Declaration of an Array of Arrays:

data_type[][] array_name = {
{valueR1C1, valueR1C2, ....},
{valueR2C1, valueR2C2, ....}
};

For example: int[][] arr = {{1, 2}, {3, 4}};

Allocation of values in an Array of Arrays

Java

// Allocation of values in an Array of Arrays
class GFG {
    public static void main(String[] args)
    {

        int[][] arr = new int[20][30];
        arr[0][0] = 100;

        System.out.println("arr[0][0] = " + arr[0][0]);
    }
}

Output

arr[0][0] = 100

Printing complete Array of Arrays

Java

// Printing complete Array of Arrays
class GFG {
    public static void main(String[] args)
    {

        int[][] arr = { { 1, 2 }, { 3, 4 } };

        for (int i = 0; i < 2; i++)
            for (int j = 0; j < 2; j++)
                System.out.println("arr[" + i + "][" + j
                                   + "] = " + arr[i][j]);
    }
}

Output

arr[0][0] = 1
arr[0][1] = 2
arr[1][0] = 3
arr[1][1] = 4

An array of Arrays in java is actually an array of a one-dimensional array. Each row of a two-dimensional array has a length field that holds the number of columns. However, we can get both the row upper bound and the column dimensions using:

int row_bound = array_name.length;
int column_bound = array_name[0].length;

Determine the Dimension of an Array of Arrays

Java

// Determine the Dimension of an Array of Arrays
class GFG {
    public static void main(String args[])
    {
        int[][] arr = new int[10][20];
        int row_bound = arr.length;
        int column_bound = arr[0].length;
        System.out.println("Dimension 1: " + row_bound);
        System.out.println("Dimension 2: " + column_bound);
    }
}

Output

Dimension 1: 10
Dimension 2: 20

Note: It is important to understand that Java doesn’t really have two-dimensional arrays. Java arrays are inherently jagged. It has arrays of arrays. So there is no one upper bound/length of the column level.

Example:

Java

// row bound and column bounds
class GFG {
    public static void main(String args[])
    {
        int[][] arr = { { 1, 2 },
                        { 3 },
                        { 4 },
                        { 5, 6, 7, 8 },
                        { 9, 10, 11, 12, 13, 14, 15 } };
        int row_bound = arr.length;
        int column_bound1 = arr[0].length;
        int column_bound2 = arr[1].length;
        int column_bound5 = arr[4].length;
        System.out.println("Dimension 1: " + row_bound);
        System.out.println("Dimension 2: " + column_bound1);
        System.out.println("Dimension 3: " + column_bound2);
        System.out.println("Dimension 4: " + column_bound5);
    }
}

Output

Dimension 1: 5
Dimension 2: 2
Dimension 3: 1
Dimension 4: 7