PHP的extends继承关系

废话少说上代码：<?php 

Class Notify{

  protected $color = "red"; //子类也可以继承属性

  public function message(){

  return '<span style="color:'.$this->color.'">发送通知消息</span>';

  }

}

Class User extends Notify
{

  public function register(){

  return $this->message();

  }

}

Class Comment extends Notify{
  
 public function send()
{

 return $this->message();

}

}

echo (new Comment)->send();