boolean () { // More efficient implementation than default size() == 0 // we use resync() to accomplish the task. If there is an // element 0 in this FilterList, then it is not empty! // we may already have resync'd 0, which will be a fast return then, // or, if we have not resync'd 0, then we only have to filter up to // the first matching element to get a result (or the whole list // if isEmpty() is true). return resync(0) == size; }