// 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 Group by Even and Odd System.out.println(intSet.stream().collect(Collectors.groupingBy(p->((Integer)p)%2))); Prints {0=[2, 4], 1=[1, 3]}