How to Create Generic Multidimensional Array in Java?

Question

I have a reference to the type class Class<?>of the generic type Element and I want to create a two dimensional array Element[][] where the second dimension null. Is there a way to do this?

The code I have right now is:

Class<?> type = ...
int length = ...
Element[][] array = (Element[][]) Array.newInstance(type, length, 0);
for (int i=0; i < array.length; i++)
    array[i] = null;

Is there any way to do this without the loop and the extra allocated memory?

Edit ----

The second dimension being null means that its just an array of null references to arrays of Element. I am doing this so I can dynamically allocate the length of the second domension so that the arrays do not need to be the same length. So I can do something like this:

array[0] = (Element[]) Array.newInstance(type, 4);
array[1] = (Element[]) Array.newInstance(type, 1);
array[2] = (Element[]) Array.newInstance(type, 3);
array[3] = null;
array[4] = null;
array[5] = (Element[]) Array.newInstance(type, 8);

etc..

array[i] = null? Maybe you want to put null in each element of the 2nd dimension? What does Class<?> have to do with this? Your question is unclear. — user1803551
– user1803551, Commented Feb 21, 2016 at 3:57

score 2 · Accepted Answer · 2016-02-21 05:20:13Z

2

Try this.

Class<?> type = ...
int length = ...
Class<?> typeOneDimArray = Array.newInstance(type, 0).getClass();
Element[][] array = (Element[][])Array.newInstance(typeOneDimArray, length);

In general, if you want to create an N dimensional array, create an array of N-1 dimensional array.

edited Feb 21, 2016 at 5:20

answered Feb 21, 2016 at 4:22

user4910279

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2 Comments

nikdeapen Over a year ago

This works, thank you. It still feels odd that you have to create another array though.

user4910279 Over a year ago

I think there is no standard API to get array class from element class. So I create an array instance and get class of it.

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