Finding length of all arrays multidimensional array, Java

Question

I would like to use a multidimensional array to store a grid of data. However, I have not found a simple way to find the length of the 2nd part of the array. For example:

boolean[][] array = new boolean[3][5];
System.out.println(array.length);

will only output 3.

Is there another simple command to find the length of the second array? (i.e. output 5 in the same manner)

`System.out.println(array[0].length);` – Daniel Fischer Sep 19 '12 at 21:04 — Daniel Fischer, Sep 19 '12 at 21:04

score 11 · Accepted Answer · answered Sep 19 '12 at 21:05

11

Try using array[0].length, this will give the dimension you're looking for (since your array is not jagged).

answered Sep 19 '12 at 21:05

arshajii

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+1 for hinting that not all multi-dimensional arrays are necessarily square. – Brian Sep 19 '12 at 21:10

score 7 · Answer 2 · answered Sep 19 '12 at 21:57

boolean[][] array = new boolean[3][5];

Creates an array of three arrays (5 booleans each). In Java multidimensional arrays are just arrays of arrays:

array.length

gives you the length of the "outer" array (3 in this case).

array[0].length

gives you the length of the first "inner" array (5 in this case).

array[1].length

and

array[2].length

will also give you 5, since in this case, all three "inner" arrays, array[0], array[1], and array[2] are all the same length.

score 1 · Answer 3 · answered Sep 19 '12 at 21:06

1

array[0].length would give you 5

answered Sep 19 '12 at 21:06

PermGenError

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score 1 · Answer 4 · answered Sep 19 '12 at 21:06

1

int a = array.length;

if (a > 0) {
  int b = array[a - 1].length;
}

should do the trick, in your case a would be 3, b 5

answered Sep 19 '12 at 21:06

user28061

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This will cause an `IndexOutOfBounds` exception. – arshajii Sep 19 '12 at 21:08
Except that this will give you an `ArrayIndexOutOfBoundsException` since `a` is the length of `array`. You probably just meant to use `0` – Brian Sep 19 '12 at 21:08
@Brian fixxed it - it's too late for me -.- – user28061 Sep 19 '12 at 21:11
Well, I +1'd because of your bounds check with `a > 0`, but Idk who downvoted, sorry. – Brian Sep 19 '12 at 21:12
@Brian I am not even sure if it is necessary, because new boolean[0][5] wouldn't work anyway, right? – user28061 Sep 19 '12 at 21:15
1

@user28061 Sure it would (and does). You can make 0-length arrays, and that's exactly what `new boolean[0][5]` does. – Brian Sep 19 '12 at 21:27
Why use `array[a - 1].length` when you could use `array[0].length`? – arshajii Sep 19 '12 at 21:49
1

@A. R. S. If `new boolean[0]` works, `array [0]` is out of bounds. – user28061 Sep 19 '12 at 21:56
Yes I understand, but you could just do `if (array.length > 0) { int b = array[0].length; }` instead of defining that `a` variable right? – arshajii Sep 19 '12 at 22:06

score 0 · Answer 5 · answered Nov 12 '16 at 22:48

You want to get the length of the inner array in a 3 dimensional array

e.g.

int ia[][][] = new ia [4][3][5];
System.out.print(ia.length);//prints 4
System.out.print(ia[0].length);//prints 3
System.out.print(ia[0].[0].length); // prints 5 the inner          array in a three  D array

By induction: For a four dimensional array it's:

ia[0].[0].[0].length

......

Finding length of all arrays multidimensional array, Java

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