Courses

package AssociativeArrays_Exsercise;

import java.util.*;

public class Courses {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        Map<String, List<String>> courses = new LinkedHashMap<>();
        String input = scanner.nextLine();
        while (!input.equals("end")) {
            String[] tokens = input.split(" : ");
            String course = tokens[0];
            String student = tokens[1];
            courses.putIfAbsent(course,new ArrayList<>());
            courses.get(course).add(student);

            input = scanner.nextLine();
        }
        courses.entrySet().stream().sorted((f,s) -> Integer.compare(s.getValue().size(),f.getValue().size())
        ).forEach(c -> {
            System.out.printf("%s: %d%n",c.getKey(),c.getValue().size());
            c.getValue().sort((s,v) -> s.compareTo(v));
            for (Object name : c.getValue()) {
                System.out.println("-- " + name);
            }
        });
    }
}