設計模式 - php組合模式的一個例子相關的問題

<code><?php
abstract class MenuComponent
{
    abstract function add(MenuComponent $component);
    abstract function remove(MenuComponent $component);
    abstract function getName();
    abstract function displayOperation();

}

class MenuComposite extends MenuComponent
{
    private $_items = array(); 
    private $_name = null;

    function __construct($name)
    {
        $this->_name = $name;
    }

    function remove(MenuComponent $component){

    }

    function add(MenuComponent $component)
    {
        $this->_items[$component->getName()] = $component;
    }

    function getName(){
        return $this->_name;
    }

     public function displayOperation() {  
        static $align = '|';  

            $align .='';  
        
        echo $this->_name, " <br/>";  
        foreach($this->_items as $name=> $item) {  
            echo $align;  
            $item->displayOperation();  
        }  
    }  
}

class Client
{
    static function displayMenu()
    {
        $subMenu1 = new MenuComposite('submenu1');
        $subMenu1->add($subMenu1);
        $subMenu1->displayOperation();
    }
}

Client::displayMenu();</code>

輸出是無限循環的
submenu1
|submenu1
|submenu1
...

為什麼會這樣，第一次遞歸呼叫displayOperation（）後foreach裡面應該是空，就停止了，為什麼會無限迴圈？

回覆內容：

<code><?php
abstract class MenuComponent
{
    abstract function add(MenuComponent $component);
    abstract function remove(MenuComponent $component);
    abstract function getName();
    abstract function displayOperation();

}

class MenuComposite extends MenuComponent
{
    private $_items = array(); 
    private $_name = null;

    function __construct($name)
    {
        $this->_name = $name;
    }

    function remove(MenuComponent $component){

    }

    function add(MenuComponent $component)
    {
        $this->_items[$component->getName()] = $component;
    }

    function getName(){
        return $this->_name;
    }

     public function displayOperation() {  
        static $align = '|';  

            $align .='';  
        
        echo $this->_name, " <br/>";  
        foreach($this->_items as $name=> $item) {  
            echo $align;  
            $item->displayOperation();  
        }  
    }  
}

class Client
{
    static function displayMenu()
    {
        $subMenu1 = new MenuComposite('submenu1');
        $subMenu1->add($subMenu1);
        $subMenu1->displayOperation();
    }
}

Client::displayMenu();</code>

輸出是無限循環的
submenu1
|submenu1
|submenu1
...

為什麼會這樣，第一次遞歸呼叫displayOperation（）後foreach裡面應該是空，就停止了，為什麼會無限迴圈？

add 的實作 $this->_items[$component->getName()] = $component;

注意$subMenu1->add($subMenu1);

實例$subMenu1的屬性$_items["submenu1"]是他自己本身 $subMenu1

然後無窮下去...

類別屬性$this->item一直是你實例化傳進去的對象，所以，這個displayOperation()方法就一直循環下去了