YOLO

src/com/university/Course.java

 package com.university;
 
+import java.util.ArrayList;
+import java.util.List;
+
 public class Course {
 
     String ID;
+    String name;
+    Department department;
+    Professor professor;
+    List<Student> students;
+    int credit;
     public Course(String ID, String name, Department department, Professor professor, int credit) {
-
+        this.ID = ID;
+        this.name = name;
+        this.department = department;
+        this.professor = professor;
+        this.credit = credit;
+        this.students = new ArrayList<>();
     }
 
     public String getID(){
-        return null;
+        return this.ID;
     }
 
     public Department getDepartment(){
-        return null;
+        return this.department;
     }
 
     public String getName() {
-        return null;
+        return this.name;
     }
 
     public Student[] getStudents() {
-        return null;
+        Student[] std = new Student[this.students.size()];
+        for (int i = 0 ; i < this.students.size(); i++)
+            std[i] = this.students.get(i);
+        return std;
     }
 
     public Professor getProfessor() {
-        return null;
+        return this.professor;
     }
 
     public int getCredit() {
-        return 0;
+        return this.credit;
     }
 
     public void enrollStudent(Student student){
-
+        if (student.getDepartment().getName().equals(this.department.getName()))
+            this.students.add(student);
     }
 
 }

src/com/university/Department.java

@@ -25,7 +25,7 @@ public class Department {
     }
 
     public Student[] getStudents(){
-        return (Student[])this.students.toArray();
+        return this.students.toArray(new Student[this.students.size()]);
     }
 
     public void removeStudent(Student student){
@@ -37,7 +37,7 @@ public class Department {
     }
 
     public Course[] getCourses(){
-        return (Course[])this.courses.toArray();
+        return this.courses.toArray(new Course[this.courses.size()]);
     }
 
     public void removeCourse(Course course){
@@ -49,7 +49,7 @@ public class Department {
     }
 
     public Professor[] getProfessors(){
-        return (Professor[])this.professors.toArray();
+        return this.professors.toArray(new Professor[this.professors.size()]);
     }
 
     public void removeProfessor(Professor professor){

src/com/university/Student.java

 package com.university;
 
-public class Student {
+import java.util.ArrayList;
+import java.util.List;
 
+public class Student {
+    String Name;
+    String ID;
+    String major;
+    Department department;
+    List<Course> courses;
     public Student(String name, String ID, String major, Department department) {
-
+        this.Name = name;
+        this.ID = ID;
+        this.major = major;
+        this.department = department;
+        this.courses = new ArrayList<>();
     }
 
     public String getName() {
-        return null;
+        return this.Name;
     }
 
     public String getID() {
-        return null;
+        return this.ID;
     }
 
     public String getMajor() {
-        return null;
+        return this.major;
     }
 
     public Department getDepartment() {
-        return null;
+        return this.department;
     }
 
     public Course[] getCourses() {
-        return null;
+        Course[] crs = new Course[this.courses.size()];
+        for(int i = 0 ; i < this.courses.size(); i++)
+        {
+            crs[i] = this.courses.get(i);
+        }
+        return crs;
     }
 
     public void addCourse(Course course){
-
+        this.courses.add(course);
     }
 }

src/com/university/University.java

@@ -6,7 +6,7 @@ import java.util.List;
 public class University {
     List<Department> departments = new ArrayList<>();
     public Department[] getDepartments(){
-        return (Department[])this.departments.toArray();
+        return this.departments.toArray(new Department[this.departments.size()]);
     }
 
     public void addDepartment(Department department){ this.departments.add(department);}

src/test/CourseTest.java

+package test;
+
+import com.university.Course;
+import com.university.Department;
+import com.university.Professor;
+import com.university.Student;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
 import static org.junit.jupiter.api.Assertions.*;
 
 class CourseTest {
-
+    static Department department;
+    static Professor professor;
+    static Course course;
+    static Student student;
+    @BeforeAll
+    public static void createCourse()
+    {
+        department = new Department("Computer");
+        professor = new Professor(department, "Gholam");
+        student = new Student("Roham", "1", "Software Eng", department);
+        course = new Course("1", "AP", department, professor, 0);
+        course.enrollStudent(student);
+    }
+    @Test
+    public void testCourse()
+    {
+        assertEquals("1", course.getID());
+        assertEquals("AP", course.getName());
+        assertEquals(department, course.getDepartment());
+        assertEquals(professor, course.getProfessor());
+        assertEquals(0, course.getCredit());
+        assertEquals(student, course.getStudents()[0]);
+    }
 }
\ No newline at end of file

src/test/DepartmentTest.java

+package test;
+
+import com.university.Course;
+import com.university.Department;
+import com.university.Professor;
+import com.university.Student;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class DepartmentTest {
+    static Department department;
+    static Professor professor;
+    static Course course;
+    static Student student;
+    @BeforeAll
+    public static void createDepartment()
+    {
+        department = new Department("Computer");
+        professor = new Professor(department, "Gholam");
+        student = new Student("Roham", "1", "Software Eng", department);
+        course = new Course("1", "AP", department, professor, 0);
+        department.addStudent(student);
+        department.addCourse(course);
+        department.addProfessor(professor);
+    }
+    @Test
+    public void testDepartment()
+    {
+        assertEquals("Computer", department.getName());
+        assertEquals( course, department.getCourses()[0]);
+        assertEquals( student, department.getStudents()[0]);
+        assertEquals(professor, department.getProfessors()[0]);
+        department.removeCourse(course);
+        department.removeProfessor(professor);
+        department.removeStudent(student);
+        assertEquals( 0, department.getCourses().length);
+        assertEquals( 0, department.getStudents().length);
+        assertEquals(0, department.getProfessors().length);
+    }
+}
\ No newline at end of file

src/test/ProfessorTest.java

+package test;
+
+import com.university.Course;
+import com.university.Department;
+import com.university.Professor;
+import com.university.Student;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class ProfessorTest {
+    static Department department;
+    static Professor professor;
+    static Course course;
+    static Student student;
+    @BeforeAll
+    public static void createProfessor()
+    {
+        department = new Department("Computer");
+        professor = new Professor(department, "Gholam");
+        student = new Student("Roham", "1", "Software Eng", department);
+        course = new Course("1", "AP", department, professor, 0);
+    }
+    @Test
+    public void testProfessor()
+    {
+        assertEquals("Gholam", professor.getName());
+        assertEquals(department, professor.getDepartment());
+    }
+}
\ No newline at end of file

src/test/StudentTest.java

+package test;
+
+import com.university.Course;
+import com.university.Department;
+import com.university.Professor;
+import com.university.Student;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
 import static org.junit.jupiter.api.Assertions.*;
 
 class StudentTest {
-
+    static Student student;
+    static Department department;
+    static Course c1;
+    @BeforeAll
+    public static void createStudent(){
+        department = new Department("Computer and IT Eng");
+        student = new Student("Roham", "1", "Software Eng", department);
+        c1 = new Course("1", "AP", department, new Professor(department, "Gholam"), 0);
+        student.addCourse(c1);
+    }
+    @Test
+    public void testStudentGetName(){
+        assertEquals("Roham", student.getName());
+        assertEquals("1", student.getID());
+        assertEquals("Software Eng", student.getMajor());
+        assertEquals(department, student.getDepartment());
+        assertEquals(c1, student.getCourses()[0]);
+    }
 }
\ No newline at end of file

src/test/UniversityTest.java

+package test;
+
+import com.university.*;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class UniversityTest {
+    static Department department;
+    static University university;
+
+    @BeforeAll
+    public static void createUniversity() {
+        department = new Department("Computer");
+        university = new University();
+        university.addDepartment(department);
+    }
+
+    @Test
+    public void testUniversity() {
+        assertEquals(department, university.getDepartments()[0]);
+        university.removeDepartment(department);
+        assertEquals(0, university.getDepartments().length);
+    }
+}
\ No newline at end of file