Returns a new collection of the same class as the receiver that contains all the items from the receiver collection and selected items from the argument collection. The resulting CircularQueue object will have a size that is the larger of the receiver's size or the union size of the two collections. This method includes an item from argument in the new collection only if there is no equivalent item in the receiver collection and the method has not already included. The order in which this method selects items in argument is unspecified (the program should not rely on any order.). The argument can be a Collection object or any other object that supports a makeArray method.