php 实现设计模式之 享元模式

<?php
class Book{
	public $title;
	public $author;

	public function __construct($title,$author){
		$this->author = $author;
		$this->title = $title;
	}

	public function getTitle(){
		return $this->title;
	}

	public function getAuthor(){
		return $this->author;
	}
}

class BookFactory{
	public $books;

	public function add($book){
		$this->books[] = $book;
	}

	public function getBook($title){
		if(empty($this->books[$title])){//建立title和book的对应关系。
			$this->books[$title] = new Book($title, '李白');
		}
		return $this->books[$title];
	}
}

class BookShelf{
	public $shelf;

	public function add($book){
		$this->shelf[] = $book;
	}

	public function show(){
		foreach ($this->shelf as $value){
			echo '作者 ：'.$value->getAuthor().'  标题:'.$value->getTitle();
			echo "<br/>";
		}
	}
}

class Client{
	public static function main(){
		$obj = new BookFactory();
		$shelf = new BookShelf();

		$book_1 = $obj->getBook('静夜思');
		$book_2 = $obj->getBook('望天门山');
		$book_3 = $obj->getBook('望庐山瀑布');
		$book_4 = $obj->getBook('静夜思');//book4 服用的book1.

		if($book_1 === $book_4){
			echo 'book1 is as the same as book4';
		}

		$shelf->add($book_1);
		$shelf->add($book_2);
		$shelf->add($book_3);

		$shelf->show();

	}
}

Client::main();
?>

　　UML类图如下：

补充一个实例：

<?php
//一个产品有ISBN号和名字
class Product{
	public $ISBN;
	public $name;
}

//享元类，提取出共性，同一个ISBN号对应的名字不会变，把这本书名字提取出来，放入享元对象，这样享元对象就存储了内蕴状态，外蕴状态是ISBN号码

class Book{
	public $name;
	public function __construct($name){
		$this->name = $name;
	}
	public function show(){
		echo $this->name;
	}

}

//享元对象生产工厂，传入外蕴对象，返回对应的享元对象。
class BookFactory{
	public $books = array();
	public function getBook($ISBN,$name){//维护一个对象池
		if(!isset($this->books[$ISBN])){
			$this->books[$ISBN] = new Book($name);
		}
		return $this->books[$ISBN];
	}
}

$obj = new BookFactory();
$book = $obj->getBook('1111','PHP高级程序设计');
$book2 = $obj->getBook('1111','');
$book2->show();
?>