In Java, you can define an array of multi-dimensional arrays. Before learning about multi-dimensional arrays.

In that tutorial, you learned how to create and use an array of primary data types (such as Double, int, etc.), a string array, and an object array. An array of arrays can also be created. For example,

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

A is a two-dimensional array that holds up to 12 integer elements.

Note that the array starts from 0, not 1.

You can also define a three-dimensional array. For example:

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

PersonalInfo is a 3D array that holds up to 24 string elements.

In Java, the components of a multi-dimensional array are also arrays.

If you are familiar with C++ / C, you may feel that multi-dimensional arrays work similarly in Java and C++ / C. Well, it is not. In Java, rows can have different lengths.

You will notice the difference when initializing.

How do you initialize a 2D array in Java?

Here is an example of how to initialize a 2D array in Java.

int [] [] a = {

{1, 2, 3},

{4, 5, 6, 9},

{7},

};

As mentioned, each array component a is an array in itself, and the length of each row is different.

Let’s write a program to prove it.

1. class MultidimensionalArray {
2. public static void main (String [] args) {
3. int [] [] a = {
4. {1, 2, 3},
5. {4, 5, 6, 9},
6. {7},
7. };
9. System.out.println (“Length of row 1:” + a [0] .length);
10. System.out.println (“Length of row 2:” + a [1] .length);
11. System.out.println (“Length of row 3:” + a [2] .length);
12. }
13. }

Output

Length of row 1: 3

Length of row 2: 4

Length of row 3: 1

Since each component of a multi-dimensional array is also an array ([a [0], a [1, and [a [2 are also arrays), You can use the length property to find the length of each row.

Example: Print all the elements of a 2D array using a loop

1. class MultidimensionalArray {
2. public static void main (String [] args) {
3. int [] [] a = {
4. {1, -2, 3},
5. {-4, -5, 6, 9},
6. {7},
7. };
9. for (int i = 0; i <a.length; ++ i) {
10. for (int j = 0; j <a [i] .length; ++ j) {
11. System.out.println (a [i] [j]);
12. }
13. }
14. }
15. }

Output

It may be best to use the for… each loop at all times. You can do the same with the for… each loop:

1. class MultidimensionalArray {
2. public static void main (String [] args) {
3. int [] [] a = {
4. {1, -2, 3},
5. {-4, -5, 6, 9},
6. {7},
7. };
9. for (int [] innerArray: a))
10. for (int data: innerArray) {
11. System.out.println (data);
12. }
13. }
14. }
15. }

Output

1

-2

3

-4

-5

6

9

7

How do you initialize a 3D array in Java?

You can set the 3D array in the same way as a 2D array. Consider the following example:

// test is a 3d array

int [] [] [] test = =

{

{1, -2, 3},

{2, 3, 4}

},

{

{-4, -5, 6, 9},

{1},

{2, 3}

}

};

In essence, a three-dimensional array is an array of two-dimensional arrays.

Similar to 2D arrays, rows of 3D arrays can have different lengths.

Example: A program for printing 3D array elements using loops

1. class ThreeArray {
2. public static void main (String [] args) {
3. // test is a 3d array
4. int [] [] [] test = =
5. {
6. {1, -2, 3},
7. {2, 3, 4}
8. },
9. {
10. {-4, -5, 6, 9},
11. {1},
12. {2, 3}
13. }
14. };
16. // for..each loop to iterate through elements of 3d array
17. for (int [] [] array2D: test) {
18. for (int [] array1D: array2D) {
19. for (int item: array1D) {
20. System.out.println (item);
21. }
22. }
23. }
24. }
25. }

Output

1

-2

3

2

3

4

-4

-5

6

9

1

2

3

Loop Through a Multi-Dimensional Array

You can also use a for loop inside another for loop to get the elements of a two-dimensional array (we still have to point to the two indexes):

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