第三周作业

abstract class Component
{
    public $id;
    abstract function  print();
}
class BaseWindow extends Component
{
    /**
     * @var $_sub_components Component[]
     */
    private $_sub_components;
    public function print()
    {
        foreach ($this->_sub_components as $key => $component) {
            $component->print();
        }
    }
    /**
     * @param $component Component
     * @return Component
     */
    public function addSub($component)
    {
        return $this->_sub_components[$component->id] = $component;
    }
    public function removeSub($id)
    {
        unset($this->_sub_components[$id]);
    }
}
class WindowForm extends BaseWindow
{
    public function print()
    {
        echo 'winform';
        parent::print();
    }
}
class WindowFrame extends BaseWindow
{
    public function print()
    {
        echo 'winframe';
        parent::print();
    }
}
class Button extends Component
{
    public function print()
    {
        echo 'button';
    }
}
class Label extends Component
{
    public function print()
    {
        echo 'label';
    }
}