Java Multidimensional Arrays

Learn Java multidimensional arrays with examples. Understand 2D arrays, 3D arrays, initialization, and accessing elements in nested 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,

[2-dimensional array in Java] 2-dimensional Array

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 (342) 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.

[2d array example in Java with variable length] Initialization of 2-dimensional Array

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:

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:

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:

Java Multidimensional Arrays

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