Using Dependency Injection:

Pass an instance of one class as a parameter to the constructor or a method of another class.

                 class ClassA {
                    private $sharedData;

                    public function setData($data) {
                        $this->sharedData = $data;
                    }

                    public function getData() {
                        return $this->sharedData;
                    }
                }

                class ClassB {
                    private $classA;

                    public function __construct(ClassA $classA) {
                        $this->classA = $classA;
                    }

                    public function processData() {
                        $data = $this->classA->getData();
                        // Process data here
                    }
                }

                // Example usage
                $classA = new ClassA();
                $classB = new ClassB($classA);

                $classA->setData("Hello, World!");
                $classB->processData();


                

Using a Singleton Pattern:

Implement a singleton pattern to create a single instance of a class that manages shared data. Other classes can then access this instance.

                class SharedDataSingleton {
                    private static $instance;
                    private $sharedData;

                    private function __construct() {}

                    public static function getInstance() {
                        if (!self::$instance) {
                            self::$instance = new SharedDataSingleton();
                        }
                        return self::$instance;
                    }

                    public function setData($data) {
                        $this->sharedData = $data;
                    }

                    public function getData() {
                        return $this->sharedData;
                    }
                }

                class ClassA {
                    public function setData($data) {
                        SharedDataSingleton::getInstance()->setData($data);
                    }

                    public function getData() {
                        return SharedDataSingleton::getInstance()->getData();
                    }
                }

                class ClassB {
                    public function processData() {
                        $data = SharedDataSingleton::getInstance()->getData();
                        // Process data here
                    }
                }

                // Example usage
                $classA = new ClassA();
                $classB = new ClassB();

                $classA->setData("Hello, World!");
                $classB->processData();