Multi-Dimensional arrays are the arrays of arrays i.e elements of these arrays store the reference of another array. E.g. [[1,2,3],[3,4,5],[6,7,8]] is an array of length 3 and at 0th index there is an reference to another array [1,2,3] likewise at 1th and 2th index are reference to arrays [3,4,5] and [6,7,8] respectively.

• Syntax:-

  • data_type[1st Dimension][2nd Dimension][]...[nth Dimension] array_name = new int[size 1D][size 2D]..[size nthD];
  • data_type - Type of data to be stored i.e int,char,class etc;
  • dimension - The dimension of array i.e 1D, 2D, 3D..etc.
  • array_name - Name of the array.
  • sizes - size of the dimensions respectively. Must be int or short.

• Examples :-

int[][] twoD_arr = new int[2][2]; // 2D array
int[][] threeD-arr = new int[3][3][3]; //3D array

• Size of multi dimensional array can be calculated by multiplying the size of all the dimension. i.e int [][] arr = new int[3][3]; can store total of (3x3) i.e 9 elements. int[][][] arr = new int[3][4][6]; can store total of (3x4x6) i.e 72 elemnets.

• We have discuss 2d array in Arrays. How to declare and instantiate them. How to access the elements of 2D array.
• e.g

int[][] arr = new int[2][2];
a[0][0] = 1;
a[0][1] = 2;
a[1][0] = 3;
a[1][1] = 4;
for(int i = 0; i<arr.length; i++){
    for(int j =0; j < arr.length; j++){
        System.out.print(a[i][j]);
    }
    System.out.println(); //next line after printing one row
}

Output :-

1 2
3 4

Three Dimensional array

• It's an complex form of an multi-dimension array.
• For better understanding, three dimension array are arrays of 2D arrays.
• { Array Index[0,1,2] { row index[0,1,2] { columnindex[0,1,2] } }

}

• Indirect Method :-

• Declaration and Instantiation :-

  •       For example : int[][][] arr = new int[10][20][30
          ```
    
    

• Initialization :-

  • array_name[array_index][row_index][column-index] = value;
  • array_name[0][0][0] = 1;

• Direct Method of Declaration :-

• Declaration and Instantiation :-

  data_type[][][] array_name = {
      {
          {valueA1R1C1, valueA1R1C2, valueA1R1C3,..},
          {valueA1R2C1, valueA1R2C2, valueA1R2C3,..}
      },
      {
          {valueA2R1C1, valueA2R1C2, valueA2R1C3,..}
          {valueA2R2C1, valueA2R2C2, valueA2R2C3,..}
  
      }
  }
  

• For Example :-

int[][][] arr = {
    {
        {1,2,3},
        {4,5,6},
        {7,8,9}
    },
    {
        {10,20,30},
        {40,50,60},
        {70,80,90}
    }
} //array of 2D arrays.

• Accessing the 3D Array :-
  • For Example :-

  int [][][] arr = {
      {
          {1,2,3},
          {4,5,6},
          {7,8,9}
      },
      {
          {10,20,30},
          {40,50,60},
          {70,80,90}
      }
  };
  int len = arr.length;
  // accessing the index of 3D array
  for(int i = 0; i<len; ++i){ 
      // accessing the index of 2D array
      // 2D arraya are at index of 3D array therefore arr[i].length
      // gives the length of 2D array
      for(int j = 0; j<arr[i].length; ++j){
          // accesing the index of array
          // arrays are at index of 2D array therefore
          // arr[j].length gives the length of array
          for(int k = 0; k<arr[i][j].length; ++k){
              System.out.println("arr["+i+"]["+j+"]["+k+"] is : "+arr[i][j][k] );
          }
      }
  }

  Output :-

  arr[0][0][0] is : 1
  arr[0][0][1] is : 2
  arr[0][0][2] is : 3
  arr[0][1][0] is : 4
  arr[0][1][1] is : 5
  arr[0][1][2] is : 6
  arr[0][2][0] is : 7
  arr[0][2][1] is : 8
  arr[0][2][2] is : 9
  arr[1][0][0] is : 10
  arr[1][0][1] is : 20
  arr[1][0][2] is : 30
  arr[1][1][0] is : 40
  arr[1][1][1] is : 50
  arr[1][1][2] is : 60
  arr[1][2][0] is : 70
  arr[1][2][1] is : 80
  arr[1][2][2] is : 90
  

  • If want to print in a tabular format just use print instead of println and in the print method write arr[i][j][k]+" " and write empty println method after 2nd and 3rd loop. See code of ThreeDimArray.java.