java - Synced TreeSet Cast? -

i using treeset in java hold list of integers:

treeset<integer> num = new treeset<integer>();

since application has multiple threads, want able access synchronously. i'm using collections.synchronizedsortedset(num); , returns collections$sortedset. problem cannot cast treeset- can cast sortedset. cannot change class of num object, must cast treeset.

does know how might otherwise cast collections$sortedset treeset, or method synchronize treeset?

there no such implementation, can make 1 on. extend treeset, , override it's methods synchronized methods.

for example:

public class mysyncedtreeset extends treeset {     @override     public synchronized boolean isempty() {         return super.isempty();     }      @override     public synchronized boolean contains(object o) {         return super.contains(o);     }      // , same other methods }