public static void main(String[] args) {

String[] names = {"John", "Peter", "Susan", "Kim", "Jen",

"George", "Alan", "Stacy", "Steve", "john"};

Map<String, Long> map1 = Stream.of(names).map(e -> e.toUpperCase()).collect(

Collectors.groupingBy(e -> e, Collectors.counting()));

System.out.println(map1);

Map<Character, Long> map2 = Stream.of(names)

.collect(Collectors.groupingBy(e -> e.charAt(0), TreeMap::new,

Collectors.counting()));

System.out.println(map2);

int[] values = {2, 3, 4, 1, 2, 3, 2, 3, 4, 5, 1, 421};

IntStream.of(values).mapToObj(e -> e)

.collect(Collectors.groupingBy(e -> e, TreeMap::new, Collectors.counting())).

forEach((k, v) -> System.out.println(k + " occurs " + v + (v > 1 ? " times " : " time ")));

MyStudent[] students = {new MyStudent("John", "Lu", "CS", 32, 78),

new MyStudent("Susan", "Yao", "Math", 31, 85.4),

new MyStudent("Kim", "Johnson", "CS", 30, 78.1)};

System.out.printf("%10s%10s\n", "Department", "Average");

Stream.of(students).collect(Collectors.

groupingBy(MyStudent::getMajor, TreeMap::new,

Collectors.averagingDouble(MyStudent::getScore))).

forEach((k, v) -> System.out.printf("%10s%10.2f\n", k, v));

}