Java Multidimensional Arrays

Before we learn about the multidimensional array, make sure you know about Java array.

A multidimensional array is an array of arrays. Each element of a multidimensional array is an array itself. For example,

int[][] a = new int[3][4];

Here, we have created a multidimensional array named a. It is a 2-dimensional array, that can hold a maximum of 12 elements,

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

Let’s take another example of the multidimensional array. This time we will be creating a 3-dimensional array. For example,

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

Here, data is a 3d array that can hold a maximum of 24 (3*4*2) elements of type String.

How to initialize a 2d array in Java?

Here is how we can initialize a 2-dimensional array in Java.

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

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

Example: 2-dimensional Array

class MultidimensionalArray {
    public static void main(String[] args) {

        // create a 2d array
        int[][] a = {
            {1, 2, 3}, 
            {4, 5, 6, 9}, 
            {7}, 
        };
      
        // calculate the length of each row
        System.out.println("Length of row 1: " + a[0].length);
        System.out.println("Length of row 2: " + a[1].length);
        System.out.println("Length of row 3: " + a[2].length);
    }
}

Output:

Length of row 1: 3
Length of row 2: 4
Length of row 3: 1

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

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

Example: Print all elements of 2d array Using Loop

class MultidimensionalArray {
    public static void main(String[] args) {

        int[][] a = {
            {1, -2, 3}, 
            {-4, -5, 6, 9}, 
            {7}, 
        };
      
        for (int i = 0; i < a.length; ++i) {
            for(int j = 0; j < a[i].length; ++j) {
                System.out.println(a[i][j]);
            }
        }
    }
}

Output:

1
-2
3
-4
-5
6
9
7

We can also use the for…each loop to access elements of the multidimensional array. For example,

class MultidimensionalArray {
    public static void main(String[] args) {

        // create a 2d array
        int[][] a = {
            {1, -2, 3}, 
            {-4, -5, 6, 9}, 
            {7}, 
        };
      
        // first for...each loop access the individual array
        // inside the 2d array
        for (int[] innerArray: a) {
            // second for...each loop access each element inside the row
            for(int data: innerArray) {
                System.out.println(data);
            }
        }
    }
}

Output:

1
-2
3
-4
-5
6
9
7

In the above example, we are have created a 2d array named a. We then used for loop and for...each loop to access each element of the array.

How to initialize a 3d array in Java?

Let’s see how we can use a 3d array in Java. We can initialize a 3d array similar to the 2d array. For example,

// test is a 3d array
int[][][] test = {
        {
          {1, -2, 3}, 
          {2, 3, 4}
        }, 
        { 
          {-4, -5, 6, 9}, 
          {1}, 
          {2, 3}
        } 
};

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

Example: 3-dimensional Array

class ThreeArray {
    public static void main(String[] args) {

        // create a 3d array
        int[][][] test = {
            {
              {1, -2, 3}, 
              {2, 3, 4}
            }, 
            { 
              {-4, -5, 6, 9}, 
              {1}, 
              {2, 3}
            } 
        };

        // for..each loop to iterate through elements of 3d array
        for (int[][] array2D: test) {
            for (int[] array1D: array2D) {
                for(int item: array1D) {
                    System.out.println(item);
                }
            }
        }
    }
}

Output:

1
-2
3
2
3
4
-4
-5
6
9
1
2
3