In Java you can do this
int[][] i = new int[10][];
Does this just create 10 empty arrays of int? Does it have other implications?
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1It should be int[][] i = new int[10][];Sudhanshu Umalkar– Sudhanshu Umalkar2013-03-20 02:50:05 +00:00Commented Mar 20, 2013 at 2:50
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See this answer: stackoverflow.com/a/7913679/1427124DaoWen– DaoWen2013-03-20 02:53:54 +00:00Commented Mar 20, 2013 at 2:53
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5 Answers
It creates a 10-entry array of int[]. Each of those 10 array references will initially be null. You'd then need to create them (and because Java doesn't have true multidimensional arrays, each of those 10 int[] entries can be of any length).
So for instance:
int i[][] = new int [10][];
i[0] = new int[42];
i[1] = new int[17];
// ...and so on
Comments
Executing your code creates an array of size 10, each element of which can hold a reference to a int[], but which are all initialized to null.
In order to use the int[]s, you would have to create new int[] for each of the element, something like this:
for (int n = 0; n < 10; n++)
i[n] = new int[10]; // make them as large as you need
Comments
Yes, it does; however, each of those arrays are null. You have to then initialize each of those sub-arrays, by saying int[10][0] = new int[MY_SIZE], or something similar. You can have arrays with different lengths inside the main array; for example, this code would work:
int[][] i = new int[10][];
for(int ind = 0; ind<10;ind++){
i[ind]=new int[ind];
}
It is just an array of arrays.
Comments
Here you create ten new int[0] arrays. You have to manually initialize it, it's useful when you don't need square matrix:
int[][] array = new int[10][];
for (int i = 0; i < array.length; i++) {
array[i] = new int[i];
}
If you need square matrix you can do:
int[][] array = new int[10][10];
And it will be initialized with default values.
Comments
That is just the declaration, you need to initialize it. The 10 arrays would be null initially.
3 Comments
DaoWen
Since Java isn't C, it will actually initialize all the slots to 0, or
null, depending on if it's an int or reference type.
T.J. Crowder
@DaoWen: No, it will initialize the slots to
null, as i is an array of int[]. Each of those still needs to be created (and when they are, their slots will be initialized to 0).DaoWen
@T.J.Crowder - You're right, in this case the empty
[] on the end means there are no actual ints present to initialize to 0. I was editing my comment when you replied—thanks for pointing that out though.