void (String[] args) { // Downcast examples final Collection<Number> numbers1 = new ArrayList<Number>(1); Collection<Integer> integers1 = CollectionHelper.convertDown(numbers1); integers1.hashCode(); // Upcast example final Collection<Integer> integers4 = new ArrayList<Integer>(1); final Collection<Number> numbers4 = CollectionHelper.<Number>convertUp(integers4); numbers4.hashCode(); }