PHP中的封装技术及应用

class MyClass {
    public $publicProperty;

    public function publicMethod() {
        echo "This is a public method.";
    }
}

$myObject = new MyClass();
$myObject->publicProperty = "Public property value";
echo $myObject->publicProperty;  // 打印输出：Public property value
$myObject->publicMethod();  // 打印输出：This is a public method.

class MyClass {
    protected $protectedProperty;

    protected function protectedMethod() {
        echo "This is a protected method.";
    }
}

$myObject = new MyClass();
$myObject->protectedProperty = "Protected property value";  // 报错，无法直接访问protected属性
$myObject->protectedMethod();  // 报错，无法直接调用protected方法

class MyClass {
    private $privateProperty;

    private function privateMethod() {
        echo "This is a private method.";
    }
}

$myObject = new MyClass();
$myObject->privateProperty = "Private property value";  // 报错，无法直接访问private属性
$myObject->privateMethod();  // 报错，无法直接调用private方法

class DB {
    private $conn;

    public function __construct($host, $user, $passWord, $database) {
        $this->conn = new Mysqli($host, $user, $password, $database);
        if ($this->conn->connect_error) {
            die("Connection failed: " . $this->conn->connect_error);
        }
    }

    public function query($sql) {
        return $this->conn->query($sql);
    }

    // 其他数据库操作方法...
}

$db = new DB("localhost", "username", "password", "database");
$result = $db->query("SELECT * FROM users");
while ($row = $result->fetch_assoc()) {
    echo $row["username"];
}

class APIClient {
    private $apiUrl;

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

    public function get($endpoint, $params = []) {
        $url = $this->apiUrl . "/" . $endpoint . "?" . Http_build_query($params);
        return file_get_contents($url);
    }

    public function post($endpoint, $data = []) {
        $options = [
            "http" => [
                "method" => "POST",
                "header" => "Content-type: application/x-www-fORM-urlencoded",
                "content" => http_build_query($data)
            ]
        ];
        $context = stream_context_create($options);
        return file_get_contents($this->apiUrl . "/" . $endpoint, false, $context);
    }

    // 其他API调用方法...
}

$client = new APIClient("https://api.example.com");
$response = $client->get("users", ["page" => 1, "limit" => 10]);
echo $response;

class File {
    private $filePath;

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

    public function read() {
        return file_get_contents($this->filePath);
    }

    public function write($data) {
        file_put_contents($this->filePath, $data);
    }

    // 其他文件操作方法...
}

$file = new File("path/to/file.txt");
$file->write("Hello, world!");
echo $file->read();