ConcurrentLinkedQueue declaration problem

[Kaarthick Ramamoorthy]

Hi,

  ConcurrentLinkedQueue<ArrayList<String>>[] queue = 
new ConcurrentLinkedQueue<ArrayList<String>>[5];  

I would like to have array of queues that contains arrylist of strings. When I tried to declare as mentioned above, I could not.

The error thrown is, "cannot create a generic array of ConcurrentLinkedQueue<ArrayList<String>>"

Please help me.

[Ernest Friedman-Hill]

Yep, you cannot construct an array of a parameterized type. You have to create the array as the unparameterized version, then cast it, and live with the warning:

ConcurrentLinkedQueue<ArrayList<String>>[] queue =
(ConcurrentLinkedQueue<ArrayList<String>>[]) new ConcurrentLinkedQueue[5];

Instead of using an array, use a collection!

[Jim Yingst]

Rather than "live with the warning", you can put the offending code in a small private method, then tell the compiler to ignore that particular warning using the SuppressWarnings annotation:

    public static void main(String... args) throws Exception {
        ConcurrentLinkedQueue<ArrayList<String>>[] queue = makeClqArray(5);
    }
 
    @SuppressWarnings({"unchecked"})
    private static ConcurrentLinkedQueue<ArrayList<String>>[] makeClqArray(int size) {
        return (ConcurrentLinkedQueue<ArrayList<String>>[]) new ConcurrentLinkedQueue[size];
    }

It's also possible to put SuppressWarnings on the entire class, but that's usually not a good idea, as these warnings are a good thing in general, and you don't want to start ignoring all warnings.

But really, you're much better off just following EFH's later advice:

[EFH]: Instead of using an array, use a collection!

Arrays and generics don't mix well. Collections and generics do. If you're using generics at all, prefer collections whenever possible.

[Kaarthick Ramamoorthy]

Thank you Ernest & Jim.