Java: How to initialize a fixed length List of List?

I have a list of String[] that contains some data returned from a database

List<String[]> x;

Now for each "x" I have to store its relative Ys. (Imagine that "x" contains the elements returned from a "SELECT DISTINCT xColumn1, xColumn2 FROM table" and now for each element I have to store the data from another query).

Y's elements are going to be stored here:

List<List<String[]>> yElements;

I've read that I can declare a fixed length list, but I don't know how. This is what I have done:

yElements = Arrays.asList(new List<String[]>[x.sixe()]);

Netbeans told me "generic array creation" error.

I also want to tell you that I MUST have a fixed lenght list to store a List of String[ ] in a specific index of this List of Lists. (If you can show me how to do with an array it would be great, too!) Thanks.

If you want your lists to be absolutely fixed size, you could use the native arrays. They can be multi-dimensional so for example you can have String[][] x or `String[][][] y'.

Honestly however, your approach is a bit confusing and not that crisp from a design point of view.

Why not, similarly to as was suggested in the comment, have an object which has both columns (xColumn1, xColumn2), and then have the Y elements in a separate object, which can then be associated with the first one?

so:

class XDetails
{
   String xColumn1;
   String xColumn2;

   YDetails relatedY;
   ...
}

class YDetails
{
   ... fields of Y ...

}

Then you can have an array or List<XDetails>