php单例模式(Singleton Pattern)实例教程

class DatabaseConnection {
  private static $db;
  private static $_handle = null;

  public static function get() {
    if ( self::$db == null ){
      echo __LINE__;
      self::$db = new DatabaseConnection();
    }
    return self::$_handle;
  }

  private function __construct() {
    $dsn = 'mysql://root:password@localhost/photos';
    self::$_handle = 123;
  }

}

print( "Handle = ".DatabaseConnection::get()."\n" );
print( "Handle = ".DatabaseConnection::get()."\n" );
?>

9Handle = 123 Handle = 123 [Finished in 0.1s]

例2，php单例模式。

class DatabaseConnection
{
  public static function get()
  {
    static $db = null;//此处将示例1的静态成员变为静态变量
    if ( $db == null ){
      echo __LINE__;
      $db = new DatabaseConnection();
    }
    return $db;
  }

  private $_handle = null;//此处将表示示例1的静态去除

  private function __construct()
  {
    $dsn = 'mysql://root:password@localhost/photos';
    $this->_handle =123;
  }
  //此处新增获取私有成员$_handle的方法
  public function handle()
  {
    return $this->_handle;
  }
}

print( "Handle = ".DatabaseConnection::get()->handle()."\n" );
print( "Handle = ".DatabaseConnection::get()->handle()."\n" );
?>

8Handle = 123 Handle = 123 [Finished in 0.1s] 这两个示例个人偏好第二个 四。限度可生成实例的个数

class DatabaseConnection {
  public static function get($persistent_id=0) {//传入一个标识
    static $db = array();//此处改为数组
    if ( !array_key_exists($persistent_id, $db) ) {
      echo __LINE__;
      $db[$persistent_id] = new DatabaseConnection();
    }
    return $db[$persistent_id];
  }

  private $_handle = null;

  private function __construct() {
    $dsn = 'mysql://root:password@localhost/photos';
    $this->_handle =123;
  }
  //此处新增获取私有成员$_handle的方法
  public function handle() {
    return $this->_handle;
  }
}

print( "Handle = ".DatabaseConnection::get(1)->handle()."\n" );
print( "Handle = ".DatabaseConnection::get(2)->handle()."\n" );
print( "Handle = ".DatabaseConnection::get(2)->handle()."\n" );
?>

6Handle = 123 6Handle = 123 Handle = 123 [Finished in 0.1s] 补充，利用static静态化的方法使我们可以轻松地实现php的单例模式。 当然也可以使用全局变量存储，但是这种方法仅适用于较小的应用程序。 在较大的应用程序中，应避免使用全局变量，并使用对象和方法访问资源。