創(chuàng)建被調(diào)用者的工作不再由調(diào)用者來完成，因此稱為控制反轉(zhuǎn);

<?php

interface IDeviceWriter {
    public function saveToDevice();
}

class Business {
    private $writer;

    public function setWriter($writer) {
        $this->writer = $writer;
    }

    public function save() {
        $this->writer->saveToDevice();
    }
}

class FloppyWriter implements IDeviceWriter {
    public function saveToDevice()
    {
        echo __METHOD__ . PHP_EOL;
    }
}

class UsbWriter implements IDeviceWriter {
    public function saveToDevice()
    {
        echo __METHOD__ . PHP_EOL;
    }
}

$biz = new Business();
$biz->setWriter(new FloppyWriter());
$biz->save();

$biz->setWriter(new UsbWriter());
$biz->save();

參考資料：https://segmentfault.com/a/1190000002411255