从手册中查到的解释是：

Iterator extends Traversable {/* Methods */abstract public mixed current ( void )abstract public scalar key ( void )abstract public void next ( void )abstract public void rewind ( void )abstract public boolean valid ( void )}

当一个实现了Iterator接口的对象，被foreach遍历时，会自动调用这些方法。调用的循序是：

下面来看一下简单的代码：

class myIterator implements Iterator {      private $position = 0;      private $array = array(          "firstelement",          "secondelement",          "lastelement",      );          public function __construct() {          $this->position = 0;      }        function rewind() {          var_dump(__METHOD__);          $this->position = 0;      }        function current() {          var_dump(__METHOD__);          return $this->array[$this->position];      }        function key() {          var_dump(__METHOD__);          return $this->position;      }        function next() {          var_dump(__METHOD__);          ++$this->position;      }        function valid() {          var_dump(__METHOD__);          return isset($this->array[$this->position]);      }  }    $it = new myIterator;    foreach($it as $key => $value) {      var_dump($key, $value);      echo '---------------------------'."\n";}

以上会输出：

/Users/thanatos/Web/study/blean.php:15:string 'myIterator::rewind' (length=18)/Users/thanatos/Web/study/blean.php:35:string 'myIterator::valid' (length=17)/Users/thanatos/Web/study/blean.php:20:string 'myIterator::current' (length=19)/Users/thanatos/Web/study/blean.php:25:string 'myIterator::key' (length=15)/Users/thanatos/Web/study/blean.php:43:int 0/Users/thanatos/Web/study/blean.php:43:string 'firstelement' (length=12)---------------------------/Users/thanatos/Web/study/blean.php:30:string 'myIterator::next' (length=16)/Users/thanatos/Web/study/blean.php:35:string 'myIterator::valid' (length=17)/Users/thanatos/Web/study/blean.php:20:string 'myIterator::current' (length=19)/Users/thanatos/Web/study/blean.php:25:string 'myIterator::key' (length=15)/Users/thanatos/Web/study/blean.php:43:int 1/Users/thanatos/Web/study/blean.php:43:string 'secondelement' (length=13)---------------------------/Users/thanatos/Web/study/blean.php:30:string 'myIterator::next' (length=16)/Users/thanatos/Web/study/blean.php:35:string 'myIterator::valid' (length=17)/Users/thanatos/Web/study/blean.php:20:string 'myIterator::current' (length=19)/Users/thanatos/Web/study/blean.php:25:string 'myIterator::key' (length=15)/Users/thanatos/Web/study/blean.php:43:int 2/Users/thanatos/Web/study/blean.php:43:string 'lastelement' (length=11)---------------------------/Users/thanatos/Web/study/blean.php:30:string 'myIterator::next' (length=16)/Users/thanatos/Web/study/blean.php:35:string 'myIterator::valid' (length=17)