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javaarraysarraylistmultidimensional-array
Yiqing Rose Chen
Yiqing Rose Chen

Reputation: 73

Can I initialize a array/arraylist<int> of 2D array in Java?

Can I initialize ArrayList of 2D array, is this a thing?

So when I try to initialize this, below is my code

ArrayList<int>[][] suffle = new ArrayList<int>[row][col];

I get an error like this:

Error: Syntax error, insert "Dimensions" to complete ReferenceType

How can I fix this?

Upvotes: 4

Views: 8346

Answers (4)

Dhruv Rai Puri
Dhruv Rai Puri

Reputation: 1375

Wherever you need to use generic types within diamond brackets, you should not use primitive types such as int, double etc. Rather, respective wrapper types such as Integer and Double etc should be used.

After I saw this question being asked in many forums, I have explained this with examples on my blog as well - http://www.javabrahman.com/corejava/how-to-resolve-syntax-error-insert-dimensions-to-complete-referencetype/

(Note/Disclosure - the above link is from a blog owned by me)

Upvotes: 0

Makoto
Makoto

Reputation: 106430

It is a thing, but you have to use an object, not a primitive. This applies to all generic types.

ArrayList<Integer>[][] suffle = new ArrayList[row][col];

You're going to get some compiler warnings about the above declaration, but it is perfectly possible to do.

Depending on what it is you're doing, it might be better to use a list of lists, which will ensure type safety as oppose to the unchecked warning you'd get from the above...

List<List<Integer>> suffle = new ArrayList<>();

...or a standard two-dimensional array:

int[][] suffle = new int[row][col];

Upvotes: 5

La-comadreja
La-comadreja

Reputation: 5755

Yes, you can make a 2-dimensional array of Object types (in this case ArrayList).

But you need to write it as:

ArrayList<Integer>[][] suffle = new ArrayList[row][col];

Also make sure you initialize row and col as integer values, before you initialize the array list.

The individual elements of suffle will be declared as ArrayList types, but not initialized. You'll need to individually initialize them.

Upvotes: 0

Steve B.
Steve B.

Reputation: 57294

You can also stick entirely with primitives, i.e.

 int[][] i = new int[row][col];

Or mix and match a list of int[]

ArrayList<int[]> al = new ArrayList<>();

And almost an array of lists:

/* writing new ArrayList<Integer>[1], which is what 
you'd want to do, is not allowed for array creation.*/
ArrayList<Integer>[] a = new ArrayList[1];

Upvotes: 2

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