Maps, Lambda and Stream API - Exercise - Courses

package com.company;

import java.util.*;

public class Main {

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

       String input = "";
       Map<String, List<String>> data = new LinkedHashMap<>();



        System.out.println();
       while (!"end".equals(input = scanner.nextLine())){
           String[] list = input.split(":");
           String courseName = list[0];
           String studentName = list[1];

           data.putIfAbsent(courseName,new ArrayList<>());
           data.get(courseName).add(studentName);
       }

       data.entrySet()
               .stream()
               .sorted((a,b) -> Integer.compare(
                       b.getValue().size(),
                       a.getValue().size()))
               .forEach(e -> {
                   System.out.printf("%s: %d\n",e.getKey().trim(),e.getValue().size());
                   e.getValue()
                           .stream()
                           .sorted((a1,a2) -> a1.compareTo(a2))
                           .forEach(u -> System.out.printf("-- %s\n",u.trim()));
               });


    }
}