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;    }

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