my-plugin-admin-page-class.php

class My_Plugin_Admin_Page implements Action_Hook_SubscriberInterface
{
	public static function get_actions()
	{
		return array(
			'init' => 'configure',
			'admin_menu' => 'add_admin_page'
		);
	}
	
	public function add_admin_page()
	{
		// ...
	}
	
	public function configure()
	{
		// ...
	}
}

my-plugin-ajax.php

class My_Plugin_Ajax implements Action_Hook_SubscriberInterface
{
	const ACTION = 'my_plugin_ajax';

	public static function get_actions()
	{
		return array(
			'wp_ajax_' . self::ACTION => 'do_ajax'
		);
	}
	
	public function do_ajax()
	{
		// ...
	}
}

my-plugin-class.php

class My_plugin
{
	private $api_manager;
	
	private $booted = false;

	public function __construct()
	{
		$this->api_manager = new WP_Plugin_API_Manager();
	}

	public function get_subscribers()
	{
		return array(
			new My_Plugin_Admin_Page(),
			new My_Plugin_Ajax()
		);
	}

	public function boot()
	{
		if ($this->booted) {
			return;
		}
	
		foreach ($this->get_subscribers() as $subscriber) {
			$this->api_manager->register($subscriber);
		}
		
		$this->booted = true;
	}
}

my-plugin.php

$plugin = new My_Plugin();
$plugin->boot();