[Dúvida] Materiais bons para aprender List<> - Iniciando POO

import java.util.List;
import java.util.Map;

public class School
{

	//all teachers of a school
	private List<Teacher> teachers;

	/**
	 * Given a teacher's name, list all his lessons.
	 * 
	 * @param teacherName
	 * 			  the teacher's name, whose lessons should be listed.
	 * 			  If null, returns an empty list.
	 * 
	 * @return List<Lesson> empty, if no existent teacher matched with the given name, or
	 * 						empty, if the teacher has no lessons, otherwise
	 *         				a list with all lessons of the teacher.
	 */
	public List<Lesson> getLessons(String teacherName)
	{
		//TODO
		return null;
	}

	/**
	 * Lists all students of a given lesson.
	 * 
	 * @param lessonName
	 * 			  the lesson's name,
	 * 			  If null, returns an empty list.
     *
	 * @return List<Student> empty, if no existent lesson matched with the given name, or
	 * 						 empty, if the lesson has not students, otherwise
	 *         				 a list with all students of the lesson.
	 */
	public List<Student> getStudents(String lessonName)
	{
		//TODO
		return null;
	}

	/**
	 * Finds all classmates of a given student, that is, all other students
	 * with whom the given student attends lessons with. 
	 * 
	 * @param student
	 * 			  a student to have the classmates listed.
	 * 			  If null, returns an empty list.
	 * 
	 * @return List<Student> empty, if the given student has no classmates, otherwise
	 * 						 a list containing all classmates of the student.
	 */
	public List<Student> classmates(Student student)
	{
		//TODO
		return null;
	}

	/**
	 * For each lesson of the school, finds all students that have failed, that is, 
	 * the ones that have not achieved the minimum grade established for the lesson.
	 * 
	 * The lessons, which all students have been approved, should not be shown in the
	 * returning map.
	 * 
	 * @return Map<Lesson, List><Student>> empty, if all students of the school have been approved, or
	 *         						      empty, if the school has no lessons, otherwise
	 *         						      a map containing all students that have failed, indexed by lesson.
	 */
	public Map<Lesson, List><Student>> failed()
	{
		//TODO
		return null;
	}

	/**
	 * Lists, in descending order, the ranking of teachers calculated by the arithmetic mean of the 
	 * grades of all their students. That is, the first place of the ranking goes to the teacher, 
	 * whose arithmetic mean of the sum of the grades of all his students (considering all the teacher's lessons)
	 * is the highest among all teachers.
	 * 
	 * Only teachers, whose students have been graded, should appear in the ranking.
	 * 
	 * @return Set<Teacher> empty, if there are no teachers in the school yet, or
	 * 						empty, if all teachers have no students/lessons yet, otherwise
	 *         				a set containing teachers ordered by the arithmetic mean of the sum of the
	 *         				grades of their students.
	 */
	public List<Teacher> teachersRanking()
	{
		//TODO
		return null;
	}

	public static class Person
	{
		private String name;
	}

	public static class Teacher extends Person
	{
		//all lessons of a teacher
		private List<Lesson> lessons;
	}

	public static class Student extends Person
	{
		//only one grade per lesson
		private Map<Lesson, Double> grades;
	}

	public static class Lesson
	{
		private String name;

		private Teacher teacher;

		//the minimum grade for a student to be approved in the lesson
		private Double minimumGrade;

		private List<Student> students;
	}

}