PHP的依赖注入

闲来无事，今天兴致来了 ，看了看依赖注入，写了以下一段代码，不知道算不算依赖注入，自我感觉挺方便的，但是又说不上来！欢迎大伙前来指点！谢谢

<?php
    /**
     * 基本接口
     */
    interface noticeInterface{
        public function send($content);
        public function rec();
    }


    class mail implements noticeInterface{
        public function send($content){

        }

        public function rec(){

        }
    }

    class telsms extends mail{
        public function send($content){
            echo "用电话发短信告诉你:".$content.'<br/>';
        }
    }

    class weichart extends mail{
        public function send($content){
            echo "用微信发语音告诉你:".$content.'<br/>';
        }
    }

    class work{
        private $worker;

        public function __construct(mail $mail){
            return $this->worker = $mail;
        }
        public function dowork(){
            return $this->worker;
        }
    }

    $obj = new work(new telsms());
    $obj->dowork()->send("我是来打酱油的！");
    $obj = new work(new weichar());
    $obj->dowork()->send("我是来打酱油的！");

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