适配器模式

将某个类的接口转换成与另一个接口兼容。适配器通过将原始接口进行转换，给用户提供一个兼容接口，使得原来因为接口不同而无法一起使用的类可以得到兼容。

适配器的存在，就是为了将已存在的东西（接口）转换成适合我们需要、能被我们所利用的东西。
在现实生活中，适配器更多的是作为一个中间层来实现这种转换作用。比如电源适配器，它是用于电流变换（整流）的设备。

 

<?php
/**
 * 本实例用于  将电子书  转换为  纸质书使用
 */

interface PaperBookInterface
{
    public function open();
    public function turnPage();
    public function getPage();
}

interface EBookInterface
{
    public function unlock();
    public function pressNext();

    /**
     * returns current page and total number of pages, like [10, 100] is page 10 of 100
     * @return int[]
     */
    public function getPage();
}


/**
 * This is the adapter here. Notice it implements BookInterface,
 * therefore you don't have to change the code of the client which is using a PaperBook
 */
class EBookToPaperBookAdapter implements PaperBookInterface
{
    private $_eBook;

    public function __construct(EBookInterface $eBook)
    {
        $this->_eBook = $eBook;
    }

    /**
     * This class makes the proper translation from one interface to another.
     */
    public function open()
    {
        $this->_eBook->unlock();
    }

    public function turnPage()
    {
        $this->_eBook->pressNext();
    }

    /**
     * notice the adapted behavior here: EBookInterface::getPage() will return two integers, but BookInterface
     * supports only a current page getter, so we adapt the behavior here
     *
     * @return int
     */
    public function getPage()
    {
        return $this->_eBook->getPage()[0];
    }
}






class Book implements PaperBookInterface
{
    /**
     * @var int
     */
    private $page;

    public function open()
    {
        $this->page = 1;
    }

    public function turnPage()
    {
        $this->page++;
    }

    public function getPage(): int
    {
        return $this->page;
    }
}


class Kindle implements EBookInterface
{
    /**
     * @var int
     */
    private $page = 1;

    /**
     * @var int
     */
    private $totalPages = 100;

    public function pressNext()
    {
        $this->page++;
    }

    public function unlock()
    {
    }

    /**
     * returns current page and total number of pages, like [10, 100] is page 10 of 100
     *
     * @return int[]
     */
    public function getPage()
    {
        return [$this->page, $this->totalPages];
    }
}





$kindle = new Kindle();
$book = new EBookAdapter($kindle);

$book->open();
$book->turnPage();