java - Fix Future Unchecked Assignment Warning -

i have code pings ip addresses in given sub network. using concurrency improve performance since waiting timeout every ip address take longer otherwise:

/**  * @param subnetwork subnet scan  * @return list of internet protocol addresses reachable  * @throws ioexception  * @throws executionexception  * @throws interruptedexception  */ public static list<string> getrespondinginternetprotocoladdresses(final string subnetwork) throws ioexception,         executionexception,         interruptedexception {     final list<string> activeinternetprotocoladdresses = new arraylist<>();     int startingindex = 1;     int upperbound = 256;     int poolsize = upperbound - 1; // query concurrently best time savings     executorservice threadpool = executors.newfixedthreadpool(poolsize);     list<future<runnable>> tasks = new arraylist<>();      (int currentsubnetindex = startingindex; currentsubnetindex < upperbound;          currentsubnetindex++)     {         final int subnetindex = currentsubnetindex;          // query each internet protocol address concurrently speed purposes         future task = threadpool.submit(new thread(() ->         {             string currentinternetprotocoladdress = subnetwork + "." + subnetindex;              try             {                 if (ping.isreachable(currentinternetprotocoladdress))                 {                     activeinternetprotocoladdresses.add(currentinternetprotocoladdress);                 }             } catch (ioexception exception)             {                 exception.printstacktrace();             }         }));          tasks.add(task); // todo fix unchecked assignment warning     }      (future<runnable> task : tasks)     {         task.get();     }      threadpool.shutdown();      return activeinternetprotocoladdresses; } 

when adding new task tasks list, i'm getting unchecked assignment warning:

tasks.add(task); 

i tried generify future replacing future<runnable> created compile error instead since submit() returns future<?>.

what can fix warning?

to solve can declare tasks list<future<?>> , task future<?>.