Question on Multidimensional Array

[Yadrif Rifkins]

While studying multidimensional arrays in the K&B book I am having difficultly understanding this example (Page 228).

In the following code scores is three dimensional array (derived from the number of items (comma-separated) between the outer curly braces)

public class ArrayTest
{

  static void main(String... args) {

    int[][] scores = {{5,2,4,7}, {9,2}, {3,4}};

  }
}

But scores is only declared to be a two dimensional array so I can accept that the dimensions are being set by the list but when the declaration is changed to:

    int[][][] scores = {{5,2,4,7}, {9,2}, {3,4}};  // Added an extra dimension to the array to make it three

the code does not compile.

I am missing something here. Can someone please explain?

Thanks.

[Justin Allen]

Yadrif, I was having some problems with this and then I wrote this little test program to help:

import java.util.Arrays;

public class ArrayTest3
{

  public static void main(String... args) {

    int[][] scores = {{5,2,4,7}, {9,2}, {3,4}};
    
    for(int a =0; a<3; a++) 
    System.out.println(Arrays.toString(scores[a]));
 
    System.out.println("This number should be 3: " + scores[2][0]);
  }
}

So this is how it breaks down:
scores[0] is {5,2,4,7}, scores[1] is {9,2}, and scores[2] is {3,4}.
Then scores[0][0] is 5, scores [0][1] is 2, scores[2][0] is 3 and so on.

The key is that the first dimension of a multi-dimensional array is an array of objects, and the second dimension is the object's themselves in this case, ints.

[Yadrif Rifkins]

Thanks for the example.

Here's a sample that shows where I am still confused.

public class ArrayTest
{

  static void main(String... args) {

    // One dimensional array decaled using int[]
    int[] scores1 = {1,2,3}; 

    // Two dimensional array declared using int[][]
    int[][] scores2 = { {1,2,3}, {4,5,6} };

    // Attempt to declare and initialize a three dimensional array
    // using int[][][] causes compile errors
    //int[][][] scores3 = { {1,2,3}, {4,5,6}, {7,8,9} };

    // Using int[][][] compiles okay without the initialization
    int[][][] scores4;
  }
}

When I declare and initialize the array as (line 14):
int[][][] scores3 = { {1,2,3}, {4,5,6}, {7,8,9} };

The compile complains as follows:
ArrayTest.java:16: incompatible types
found : int
required: int[]
int[][][] scores3 = { {1,2,3}, {4,5,6}, {7,8,9} };
^
ArrayTest.java:16: incompatible types
found : int
required: int[]
int[][][] scores3 = { {1,2,3}, {4,5,6}, {7,8,9} };
.
.
. ^
9 errors


When I declare without the initialization I can use "int[][][]" but why am I not able to use "int[][][]" when I declare and initialize the array?

This only seems to be an issue with three dimensional arrays.

Thanks for the help.

[Henry Wong]

Try....

int[][][] scores3 = {{ {1,2,3}, {4,5,6}, {7,8,9} } , 
                     { {10,11,12}, {13,14,15}, {16,17,18} }, 
                     { {19,20,21}, {22,23,24}, {25,26,27} } }; 

A three dimensional array, or more correctly, an array of arrays of arrays needs to be assigned as such. In your example, you just assigned it to an array of arrays, where the outer array happens to have three elements.

Henry

[Andreas Svenkson]

As Henry said.

If you're still confused, think of it like this:

int [] = array of ints
int[][] = array of arrays of ints
int[][][] = array of arrays of arrays of ints

// Andreas

[Ikpefua Jacob-Obinyan]

Hey Guys, permit me add some more codes lets see if its clearer. @Andreas I precisely want to add to your code.

int[]      = {1,2,3};                                   // array of ints

int[][]    = { {1,2,3} };                               // array of array of ints

int[][][]  = { { {} } };                                // array of array of array 

int[][][]  = { { {1,2,3} } };                           // array of array of array of ints.


int[][][]  = { { {1,2,3}, {1,2,3}, {1,2,3} } };         // array of array of array(S) of ints.

@Yadrif, lines 5, 7 and 10 are SIMILAR, if you take a CLOSE look at line 7 you will notice that the SECOND array holds ONE array of ints.

In line 10 the SECOND array holds THREE arrays of ints. (1) {1,2,3}, (2) {1,2,3}, (3) {1,2,3}

I hope this helps.