Initialize an Array of List Objects

Question

I want to store 4 Lists of Strings to an array within index 0-3 and be able to check wether the index is filled (!=null) or not.

For that reason I need to initialize an Array of Type List, which fails in eclipse with message "Cannot create a generic array of List":

// Does not work
List<String>[] myArray = new List<String>[4];

// Does not work
List<String>[] myArray = new ArrayList<String>[4];

Doing it like promoted at Convert an ArrayList to an object array :

ArrayList<List<String>> myArrayList = new ArrayList<List<String>>();
myArrayList.add(new ArrayList<String>());
myArrayList.add(new ArrayList<String>());
myArrayList.add(new ArrayList<String>());
myArrayList.add(new ArrayList<String>());

// Does not work
List<String>[] myArray = myArrayList.toArray(new List<String>[myArrayList.size()]);

// Does not work
List<String>[] myArray = myArrayList.toArray(new ArrayList<String [myArrayList.size()]);

But why is this not working?

possible duplicate of [Initialize an Array of ArrayList](http://stackoverflow.com/questions/10227201/initialize-an-array-of-arraylist) — Kuba Spatny, Jan 21 '14 at 13:47
Because "you cannot create a generic array" in Java. This was a design choice which has to do with the mismatch between the reifiability of array types vs. non-reifiability of generic type parameters. — Marko Topolnik, Jan 21 '14 at 13:47
only Cuck Norris can initiate Interfaces: new List[myArrayList.size()]!!! :-) — nano_nano, Jan 21 '14 at 13:47
@StefanBeike There's nothing wrong with an array of interface type: `List[]`. — Marko Topolnik, Jan 21 '14 at 13:48
@Marko Topolnik: with "new List" I am able to create a List object??? — nano_nano, Jan 21 '14 at 13:51
@StefanBeike Noone here has mentioned intantiating the `List` type. — Marko Topolnik, Jan 21 '14 at 13:52
Here's a possible good [answer](http://stackoverflow.com/a/5662447/1320072)! — rockybean, Jan 21 '14 at 14:59

score 0 · Answer 1 · answered Jan 21 '14 at 13:49

0

ArrayList is generic class in Java. You cannot create an array of generic type. It is not allowed. What you can do is create a list of generic type

ArrayList<ArrayList<String>> listOfStringList = new ArrayList<ArrayList<String>>();

answered Jan 21 '14 at 13:49

Keerthivasan

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Thanks for the answer! Despite of this it does not come in my head, why Java is disallowing that. – Martin Figel Jan 21 '14 at 14:12
That is going to be design choice, it causes problems with backward compatibility, type casting issues etc. – Keerthivasan Jan 21 '14 at 14:41
Did it help you understand? – Keerthivasan Jan 22 '14 at 07:14

Initialize an Array of List Objects

1 Answers1