// Declare and Initialize the Collection Set<Integer> intSet = new HashSet<Integer>(); // Add Elements intSet.add(1); intSet.add(2); intSet.add(3); intSet.add(4); // Use the stream and Collector to find the average of all elements. System.out.println(intSet.stream().collect(Collectors.averagingInt(p->((Integer)p)))); Prints 2.5