Person

Learner
Student
Teacher
Instructor
People
Students
Instructors
Classroom

demo/src/main/java/com/example/demo/Classroom.java

@@ -0,0 +1,16 @@
+package com.example.demo;
+
+public class Classroom {
+    private Instructors instructors;
+    private Students students;
+
+    Classroom(Instructors instructors, Students students){
+        this.instructors = instructors;
+        this.students = students;
+    }
+
+    public void hostLecture(Teacher teacher, double numberOfHours){
+        teacher.lecture(students, numberOfHours);
+    }
+
+}

demo/src/main/java/com/example/demo/Instructor.java

@@ -20,7 +20,6 @@ public class Instructor extends Person implements Teacher{
 
     @Override
     public void lecture(Iterable<? extends Learner> learners, double numberOfHours) {
-        // int numberOfLearners = lengthOfIterable(learners);
         long numberOfLearners = learners
                 .spliterator()
                 .getExactSizeIfKnown();
@@ -29,11 +28,4 @@ public class Instructor extends Person implements Teacher{
         learners.forEach(o -> o.learn(numberOfHoursPerLearner));
     }
 
-//    private int lengthOfIterable(Iterable iterable){
-//        int counter = 0;
-//        for (Object o: iterable) {
-//            counter++;
-//        }
-//        return counter;
-//    }
 }

demo/src/main/java/com/example/demo/Instructors.java

@@ -0,0 +1,27 @@
+package com.example.demo;
+
+import java.util.Iterator;
+import java.util.List;
+import java.util.Spliterator;
+import java.util.function.Consumer;
+
+public class Instructors<Instructor> extends People {
+    Instructors(List instructorList) {
+        super(instructorList);
+    }
+
+    @Override
+    public Iterator iterator() {
+        return null;
+    }
+
+    @Override
+    public void forEach(Consumer action) {
+
+    }
+
+    @Override
+    public Spliterator spliterator() {
+        return null;
+    }
+}

demo/src/main/java/com/example/demo/People.java

@@ -1,12 +1,13 @@
 package com.example.demo;
 
 import java.util.ArrayList;
+import java.util.List;
 
 public abstract class People<PersonType extends Person> implements Iterable<PersonType> {
-    ArrayList<PersonType> personList;
+    List<PersonType> personList;
 
-    People(){
-        personList = new ArrayList<>();
+    People(List<PersonType> personTypeList){
+        personList = personTypeList;
     }
 
     public void add(PersonType pt){
@@ -41,7 +42,7 @@ public abstract class People<PersonType extends Person> implements Iterable<Pers
         return null;
     }
 
-    public ArrayList<PersonType> findAll(){
+    public List<PersonType> findAll(){
         return personList;
     }
 }

demo/src/main/java/com/example/demo/Students.java

@@ -1,22 +1,29 @@
 package com.example.demo;
 
+import java.util.ArrayList;
 import java.util.Iterator;
+import java.util.List;
 import java.util.Spliterator;
 import java.util.function.Consumer;
 
-public class Students extends People<Person> {
+public class Students<Student> extends People {
+
+    public Students(List<Student> students) {
+        super(students);
+    }
+
     @Override
-    public Iterator<Person> iterator() {
+    public Iterator iterator() {
         return null;
     }
 
     @Override
-    public void forEach(Consumer<? super Person> action) {
+    public void forEach(Consumer action) {
 
     }
 
     @Override
-    public Spliterator<Person> spliterator() {
+    public Spliterator spliterator() {
         return null;
     }
 }