Java Multidimensional Arrays

In this tutorial, we will learn about the Java Multidimensional array. We will see how to declare, initialize, and work with 2-dimensional arrays and 3-dimensional arrays with the help of examples.

Before we learn about the multidimensional array, make sure to learn about Jara array.

Multidimensional Arrays

A multidimensional array is an array of arrays. Each element of a multidimensional array is another array.

In the following example, we will create a multidimensional array named m. It's a 2-dimensional array of 3 * 5 that can hold a maximum of 3 * 5 = 15 elements.

int[][] m = new int[3][5];

The elements in a multidimensional array are represented in rows and columns.

Java uses zero-based indexing, so indexing of arrays in Java starts with 0 and not 1.

Let us take another example of the multidimensional array. In the following example, we will create a 3-dimensional array.

String[][][] d = new String[2][4][3];

Here above, d is a 3d array that can hold a maximum of 2 * 4 * 3 = 24

How to initialize a 2-dimensional array in Java?

We can initialize a 2-dimensional array in Java as follows.

int[][] m = {
    {1, 3, 2},
    {4, 6, 5, 8, 10},
    {9, 7}
};

As we can see above, each element of the multidimensional array is an array itself. Unlike C/C++ in Java, each row of the multidimensional array can be of different lengths.

Example of a 2-dimensional Array

In the following example, we will create a multidimensional array named m. Since each component of a multidimensional array is also an array (m[0], m[1], and m[2] are also arrays).

class TwoDimensionalArray{
    public static void main(String[] args) {
        // 2d array 
        int[][] m = {
            {1, 3, 2},
            {4, 6, 5, 8, 10},
            {9, 7}
        };

        // showing the length of each row
        System.out.println("Length of row 1: " + m[0].length);
        System.out.println("Length of row 1: " + m[1].length);
        System.out.println("Length of row 1: " + m[2].length);
    }
}

Output:

Length of row 1: 3
Length of row 1: 5
Length of row 1: 2

Here above, we are using the length attribute to calculate the length of each row.

How to access a 2-dimensional Array in Java?

To access elements of a 2-dimensional array, specify two indexes: one for the array, and one for the element inside that array.

In the following example, we will access the second element in the third array of the m multidimensional array.

int[][] m = {
    {1, 2},
    {3, 4, 5, 6},
    {7, 8}
};

int x = m[2][1];
System.out.println("The second element in the third array of 'm' is " + x);

Output:

The second element in the third array of 'm' is 8

Example: Printing all elements of a 2-dimensional array Using Loop

In the following example, we will print all elements of a 2-dimensional using a for loop.

class TwoDimensionalArray{
    public static void main(String[] args) {
        int[][] m = {
            {1, 3},
            {4, 6, 5},
            {9, 7}
        };
    
        for (int i = 0; i < m.length; ++i) {
            for (int j = 0; j < m[i].length; ++j) {
                System.out.println(m[i][j]);
            }
        }
      }
}

Output:

1
3
4
6
5
9
7

We can also use a for-each loop to access elements of the multidimensional array.

class twoDimensionalArray{
    public static void main(String[] args) {
        int[][] m = {
            {1, 3},
            {4, 6, 5},
            {9, 7}
        };

        // first for...each loop access the individual array
        for (int[] innerArray: m) {
            // second for...each loop access each element inside the row
            for (int data: innerArray) {
                System.out.println(data);
            }
        }
    }
}

Output:

1
3
4
6
5
9
7

In the above example, we have created a 2-dimensional array named m. Then we used a for...each loop inside another one to access the element of the array.

How to initialize a 3-dimensional array in Java?

We can initialize a 3-dimensional array similar to the 2-dimensional array. For example,

int[][][] three_dim = {
    {
        {1, -3, 4},
        {4, 5}
    },
    {
        {-3, 9, 6},
        {1, 2},
        {7, 8, 9}
    }
}

Basically, a 3-dimensional array is an array of 2-dimensional arrays. The rows of a 3-dimensional array can also vary in length, just like a 2-dimensional array.

Example of 3-dimensional Array

class ThreeDimensionalArray {
    public static void main(String[] args) {
        
        // create a 3d array
        int[][][] three_dim = {
            {
                {1, -3, 4},
                {8, 5}
            },
            {
                {-3, 9},
                {1, 2},
                {9}
            }
        };

        // for...each loop to iterate through elements of 3-dimensional array 
        for(int[][] arr2d: three_dim) {
            for(int[] arr1d: arr2d) {
                for(int item: arr1d) {
                    System.out.println(item);
                }
            }
        }
    }
}

Output:

1
-3
4
8
5
-3
9
1
2 
9