php protected

<?
//父类
class father{
public function a(){
echo "function a";
}
private function b(){
echo "function b";
}
protected function c(){
echo "function c";
}
}
//子类
class child extends father{
function d(){
parent::a();//调用父类的a方法
}
function e(){
parent::c(); //调用父类的c方法
}
function f(){
parent::b(); //调用父类的b方法
}
}
$father=new father();
$father->a();
$father->b(); //显示错误 外部无法调用私有的方法 Call to protected method father::b()
$father->c(); //显示错误 外部无法调用受保护的方法Call to private method father::c()
$chlid=new child();
$chlid->d();
$chlid->e();
$chlid->f();//显示错误 无法调用父类private的方法 Call to private method father::b()
?>