php中某一个类下的两个静态方法的互相调用

//静态方法aaa调用静态方法bbb

<?php 

 

class Test
{

public static function aaa(){
    echo '123456789';
    //$bbb = $this->bbb();
    $bbb = Test::bbb();
    $ccc = $this->ccc();
    echo $bbb;
    echo $ccc;
    exit;
}

public static function bbb(){
    return '111111111';
}

  public function bbb(){

         return '222222222';

  }

}