研究PHP物件導向程式設計中的多對多關係

class Student {
    private $name;
    private $courses;

    public function __construct($name) {
        $this->name = $name;
        $this->courses = array();
    }

    public function enrollCourse($course) {
        $this->courses[] = $course;
        $course->enrollStudent($this);
    }

    public function getCourses() {
        return $this->courses;
    }
}

class Course {
    private $name;
    private $students;

    public function __construct($name) {
        $this->name = $name;
        $this->students = array();
    }

    public function enrollStudent($student) {
        $this->students[] = $student;
    }

    public function getStudents() {
        return $this->students;
    }
}

class Enrollment {
    private $student;
    private $course;

    public function __construct($student, $course) {
        $this->student = $student;
        $this->course = $course;
    }
}

// 创建学生对象
$student1 = new Student("Alice");
$student2 = new Student("Bob");

// 创建课程对象
$course1 = new Course("Math");
$course2 = new Course("English");

// 学生选课
$student1->enrollCourse($course1);
$student1->enrollCourse($course2);
$student2->enrollCourse($course1);

// 输出学生的课程
echo $student1->getCourses()[0]->getName();  // 输出 "Math"
echo $student1->getCourses()[1]->getName();  // 输出 "English"
echo $student2->getCourses()[0]->getName();  // 输出 "Math"

// 输出课程的学生
echo $course1->getStudents()[0]->getName();  // 输出 "Alice"
echo $course1->getStudents()[1]->getName();  // 输出 "Bob"
echo $course2->getStudents()[0]->getName();  // 输出 "Alice"