YO

src/com/university/Course.java

+package com.university;
+
+public class Course {
+
+    String ID;
+    public Course(String ID, String name, Department department, Professor professor, int credit) {
+
+    }
+
+    public String getID(){
+        return null;
+    }
+
+    public Department getDepartment(){
+        return null;
+    }
+
+    public String getName() {
+        return null;
+    }
+
+    public Student[] getStudents() {
+        return null;
+    }
+
+    public Professor getProfessor() {
+        return null;
+    }
+
+    public int getCredit() {
+        return 0;
+    }
+
+    public void enrollStudent(Student student){
+
+    }
+
+}

src/com/university/Department.java

+package com.university;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Department {
+
+    String name;
+    List<Student> students;
+    List<Course> courses;
+    List<Professor> professors;
+    public Department(String name) {
+        this.name = name;
+        this.students = new ArrayList<>();
+        this.courses = new ArrayList<>();
+        this.professors = new ArrayList<>();
+    }
+
+    public String getName(){
+        return this.name;
+    }
+
+    public void addStudent(Student student){
+        this.students.add(student);
+    }
+
+    public Student[] getStudents(){
+        return (Student[])this.students.toArray();
+    }
+
+    public void removeStudent(Student student){
+        this.students.remove(student);
+    }
+
+    public void addCourse(Course course){
+        this.courses.add(course);
+    }
+
+    public Course[] getCourses(){
+        return (Course[])this.courses.toArray();
+    }
+
+    public void removeCourse(Course course){
+        this.courses.remove(course);
+    }
+
+    public void addProfessor(Professor student){
+        this.professors.add(student);
+    }
+
+    public Professor[] getProfessors(){
+        return (Professor[])this.professors.toArray();
+    }
+
+    public void removeProfessor(Professor professor){
+        this.professors.remove(professor);
+    }
+
+}

src/com/university/Professor.java

+package com.university;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Professor {
+    Department department;
+    String name;
+    List<Course> courses;
+    public Professor(Department department, String name) {
+        this.department = department;
+        this.name = name;
+        this.courses = new ArrayList<>();
+    }
+
+    public Department getDepartment() {
+        return this.department;
+    }
+
+    public String getName() {
+        return this.name;
+    }
+
+    public Course[] getCourses() {
+        return (Course[])this.courses.toArray();
+    }
+}

src/com/university/Student.java

+package com.university;
+
+public class Student {
+
+    public Student(String name, String ID, String major, Department department) {
+
+    }
+
+    public String getName() {
+        return null;
+    }
+
+    public String getID() {
+        return null;
+    }
+
+    public String getMajor() {
+        return null;
+    }
+
+    public Department getDepartment() {
+        return null;
+    }
+
+    public Course[] getCourses() {
+        return null;
+    }
+
+    public void addCourse(Course course){
+
+    }
+}

src/com/university/University.java

+package com.university;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class University {
+    List<Department> departments = new ArrayList<>();
+    public Department[] getDepartments(){
+        return (Department[])this.departments.toArray();
+    }
+
+    public void addDepartment(Department department){ this.departments.add(department);}
+
+    public void removeDepartment(Department department){ this.departments.remove(department);}
+}

src/test/CourseTest.java

+import static org.junit.jupiter.api.Assertions.*;
+
+class CourseTest {
+
+}
\ No newline at end of file

src/test/StudentTest.java

+import static org.junit.jupiter.api.Assertions.*;
+
+class StudentTest {
+
+}
\ No newline at end of file