Update src/main/java/Main.java

src/main/java/Main.java

@@ -70,7 +70,12 @@ public class Main {
         boolean success;
         switch (choice) {
             case 1:
-                //TODO
+                success = school.registerStudent(username, password);
+                if (success) {
+                    System.out.println(" Student registered successfully!");
+                } else {
+                    System.out.println(" Username already exists!");
+                }
                 break;
             case 2:
                 success = school.registerTeacher(username, password);
@@ -103,7 +108,12 @@ public class Main {
 
         switch (choice) {
             case 1:
-                //TODO
+                Student student = school.loginStudent(username, password);
+                if (student != null) {
+                    studentMenu(student);
+                } else {
+                    System.out.println(" Invalid username or password!");
+                }
                 break;
             case 2:
                 Teacher teacher = school.loginTeacher(username, password);
@@ -141,7 +151,7 @@ public class Main {
                     enrollInCourse(student);
                     break;
                 case 3:
-                    //System.out.print(student.getMyCoursesDisplay());
+                    System.out.print(student.getMyCoursesDisplay());
                     break;
                 case 4:
                     System.out.println(" Goodbye, " + student.getUsername() + "!");
@@ -153,7 +163,21 @@ public class Main {
     }
 
     private static void enrollInCourse(Student student) {
-       //TODO
+        System.out.print(school.getAllCoursesDisplay());
+        System.out.print("\nEnter Course ID to enroll: ");
+        int courseId = getIntInput();
+
+        Course course = school.findCourseById(courseId);
+        if (course == null) {
+            System.out.println(" Course not found! Please enter a valid ID.");
+            return;
+        }
+
+        if (student.enrollInCourse(course)) {
+            System.out.println(" Successfully enrolled in " + course.getName());
+        } else {
+            System.out.println(" You are already enrolled in this course!");
+        }
     }
 
     // ==================== TEACHER MENU ====================

src/main/java/models/Student.java

@@ -11,20 +11,28 @@ public class Student extends User {
         this.enrolledCourses = new ArrayList<>();
     }
 
-    public void enrollCourse(Course course) {
+    public boolean enrollInCourse(Course course) {
-        this.enrolledCourses.add(course);
+        if (enrolledCourses.contains(course)) {
-    }
+            return false;
-    public void showMyCourses() {
-        for (Course course : this.enrolledCourses) {
-            System.out.println(course);
         }
+        enrolledCourses.add(course);
+        course.addStudent(this);
+        return true;
     }
-    public Course getEnrolledCourses(int id) {
+
-        for (Course course : this.enrolledCourses) {
+    public List<Course> getEnrolledCourses() {
-            if (course.getId() == id) {
+        return enrolledCourses;
-                return course;
+    }
+
+    public String getMyCoursesDisplay() {
+        if (enrolledCourses.isEmpty()) {
+            return " You are not enrolled in any course yet.";
+        } else {
+            StringBuilder sb = new StringBuilder("\n My Courses:\n");
+            for (int i = 0; i < enrolledCourses.size(); i++) {
+                sb.append("  ").append(i+1).append(". ").append(enrolledCourses.get(i)).append("\n");
             }
+            return sb.toString();
         }
-        return null;
     }
 }

src/main/java/models/Teacher.java

@@ -32,22 +32,26 @@ public class Teacher extends User {
         return myCourses;
     }
 
-    public void showMyCourses() {
+    public String getMyCoursesDisplay() {
         if (myCourses.isEmpty()) {
-            System.out.println(" You don't teach any course yet.");
+            return " You don't teach any course yet.";
         } else {
-            System.out.println("\n My Courses:");
+            StringBuilder sb = new StringBuilder("\n My Courses:\n");
             for (int i = 0; i < myCourses.size(); i++) {
-                System.out.println("  " + (i+1) + ". " + myCourses.get(i));
+                sb.append("  ").append(i+1).append(". ").append(myCourses.get(i)).append("\n");
             }
+            return sb.toString();
         }
     }
 
-    public void showStudentsInCourse(Course course) {
+    public boolean checkCourseOwnership(Course course) {
+        return myCourses.contains(course);
+    }
+
+    public String getStudentsDisplayForCourse(Course course) {
         if (!myCourses.contains(course)) {
-            System.out.println(" You don't teach this course!");
+            return "You don't teach this course!";
-            return;
         }
-        course.showStudents();
+        return course.getStudentsDisplay();
     }
 }

src/main/java/services/SchoolSystem.java

@@ -16,23 +16,25 @@ public class SchoolSystem {
     }
 
     // ========== Student Management ==========
-    public void registerStudent(String username, String password) {
+    public boolean registerStudent(String username, String password) {
-        Student student = new Student(username, password);
+        if (findStudent(username) != null) {
-        this.students.add(student);
+            return false;
+        }
+        students.add(new Student(username, password));
+        return true;
     }
+
     public Student loginStudent(String username, String password) {
-        for (Student student : this.students) {
+        Student student = findStudent(username);
-            if (student.getUsername().equals(username) && student.checkPassword(password)) {
+        if (student != null && student.checkPassword(password)) {
-                return student;
+            return student;
-            }
         }
         return null;
     }
+
     private Student findStudent(String username) {
-        for (Student student : this.students) {
+        for (Student s : students) {
-            if (student.getUsername().equals(username)) {
+            if (s.getUsername().equals(username)) return s;
-                return student;
-            }
         }
         return null;
     }
@@ -63,17 +65,19 @@ public class SchoolSystem {
 
     // ========== Course Management ==========
     public boolean addCourseToSystem(String courseName) {
-        Course course = new Course(courseName);
+        for (Course c : allCourses) {
-        this.allCourses.add(course);
+            if (c.getName().equals(courseName)) {
+                return false;
+            }
+        }
+        allCourses.add(new Course(courseName));
         return true;
     }
 
     public Course findCourseById(int id) {
-       for  (Course course : this.allCourses) {
+        for (Course c : allCourses) {
-           if(course.getId() == id) {
+            if (c.getId() == id) return c;
-               return course;
+        }
-           }
-       }
         return null;
     }