How to initialize an array of lists with a specific type?

Question

I have a method that needs to return List<'MyClass>[] and need to set up a local variable to do so, but am having trouble with initialization.

I tried:

List<MyClass>[] lists = new List<MyClass>[5];

Which gave me an error of "Cannot create a generic array of List"

I tried casting an array of Objects:

List<MyClass>[] lists = (List<MyClass>[]) new Object[5];

Which gave me a casting error in runtime.

I also tried:

List<MyClass>[] lists = (List<MyClass>[]) new List[5];

Which resulted in a null pointer exception.

Anyone know what needs to be done to get this to work?

Thanks.

Nico · Accepted Answer · 2013-04-21 01:59:15Z

3

You declare a list like so (for example ArrayList):

List<MyClass> list = new ArrayList<MyClass>();

To create an array of this list you do:

List<?>[] listArray = new List<?>[]{list};

This will put your list in an array. I'm assuming that's what you want and not simply items from the list.

answered Apr 21, 2013 at 1:59

Nico

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4 Comments

That does get it to work. Thanks. Do you know of any way around having to individually create each list before adding it to the array?

How about using Arrays.asList(...) inline to avoid intermediate variables?

Honestly, no. I don't usually put my lists in an array either.

There is no way; that's basically deliberate. All arrays are always initialized to null.