PHP设计模式学习笔记： 享元模式（flyweight）

不知道为什么把flyweight翻译成享元，还有一般的应用场景在哪里？数据库？那跟单例模式比较呢？

// 享元的书对象
class FlyweightBook {
    private $author;
    private $title;    
    function __construct($author_in, $title_in) {
        $this->author = $author_in;
        $this->title  = $title_in;
    }
    function getAuthor() {
        return $this->author;
    }    
    function getTitle() {
        return $this->title;
    }
}

class FlyweightFactory {
    private $books = array();     
    function __construct() {
        $this->books[1] = NULL;
        $this->books[2] = NULL;
        $this->books[3] = NULL;
    }  
    function getBook($bookKey) {
        if (NULL == $this->books[$bookKey]) {
            $makeFunction = 'makeBook'.$bookKey;
            $this->books[$bookKey] = $this->$makeFunction(); 
        } 
        return $this->books[$bookKey];
    }    
    
    function makeBook1() {
        $book = new FlyweightBook('JK罗琳','哈利波特与魔法石'); 
        return $book;
    }
    function makeBook2() {
        $book = new FlyweightBook('JK罗琳','哈利波特与混血王子'); 
        return $book;
    }
    function makeBook3() {
        $book = new FlyweightBook('JK罗琳','哈利波特与阿兹卡班的囚徒'); 
        return $book;
    }
}

class FlyweightBookShelf {
    private $books = array();
    function addBook($book) {
        $this->books[] = $book;
    }    
    function showBooks() {
        $return_string = NULL;
        foreach ($this->books as $book) {
            $return_string .= '标题: '.$book->getAuthor().'  作者: '.$book->getTitle();
        };
        return $return_string;
    }
}

  writeln('开始测试享元模式');
 
  $flyweightFactory = new FlyweightFactory();
  $flyweightBookShelf1 =  new FlyweightBookShelf();// 制作一个新书架1
  $flyweightBook1 = $flyweightFactory->getBook(1); // 从工厂创建书1
  $flyweightBookShelf1->addBook($flyweightBook1);  // 把书1放到书架1
  $flyweightBook2 = $flyweightFactory->getBook(1); // 从工厂获取书1
  $flyweightBookShelf1->addBook($flyweightBook2);  // 把书2（其实就是书1）放到书架1， 这时候书架1上有两本书1

  writeln('测试 1 - 两本书是否是同一本书');
  if ($flyweightBook1 === $flyweightBook2) {
     writeln('1 和 2 是一样的');
  } else {
     writeln('1 和 2 是不一样的');    
  }
  writeln('');

  writeln('测试 2 - 一本书在同一个书架上出现两次');
  writeln($flyweightBookShelf1->showBooks());
  writeln('');

  $flyweightBookShelf2 =  new FlyweightBookShelf();// 制作一个新书架2
  $flyweightBook1 = $flyweightFactory->getBook(2); // 从工厂创建书2
  $flyweightBookShelf2->addBook($flyweightBook1);  // 把书2放到书架2
  $flyweightBookShelf1->addBook($flyweightBook1);  // 把书2放到书架1

  writeln('测试 3 - 书架1');
  writeln($flyweightBookShelf1->showBooks()); // 打印出了书架1上的两本书，书1
  writeln('');

  writeln('测试 3 - 书架2');
  writeln($flyweightBookShelf2->showBooks()); // 打印出了书架2上的一本书，书2
  writeln('');

  writeln('结束测试享元模式');
 
  function writeln($line_in) {
    echo $line_in.PHP_EOL;
  }

结果

开始测试享元模式
测试 1 - 两本书是否是同一本书
1 和 2 是一样的

测试 2 - 一本书在同一个书架上出现两次
标题: JK罗琳  作者: 哈利波特与魔法石标题: JK罗琳  作者: 哈利波特与魔法石

测试 3 - 书架1
标题: JK罗琳  作者: 哈利波特与魔法石标题: JK罗琳  作者: 哈利波特与魔法石标题: JK罗琳  作者: 哈利波特与混血王子

测试 3 - 书架2
标题: JK罗琳  作者: 哈利波特与混血王子

结束测试享元模式