今天学习一个对php来说意义不大的模式——享元模式
竟然意义不大为什么要学?我一直认为设计模式是不针对语言的,相对于目前的php意义不大,并不表示其本身没有意义,其在编译型的语言里还是有很多的用处的。
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享元模式的定义
享元模式是池技术的重要实现方式,其定义为:使用共享对象可有效地支持大量的细粒度的对象。太简单了,通俗地说就是把经常要使用到的对象共享起来,而不去从新创建而占用内存。其大致构成:
1、抽象享元(Flyweight)角色
此角色是所有的具体享元类的超类,为这些类规定出需要实现的公共接口。那些需要外蕴状态的操作可以通过调用商业以参数形式传入
2、具体享元(ConcreteFlyweight)角色
实现Flyweight接口,并为内部状态(如果有的话)拉回存储空间。ConcreteFlyweight对象必须是可共享的。它所存储的状态必须是内部的
3、不共享的具体享元(UnsharedConcreteFlyweight)角色
并非所有的Flyweight子类都需要被共享。Flyweigth使共享成为可能,但它并不强制共享。
4、享元工厂(FlyweightFactory)角色
负责创建和管理享元角色。本角色必须保证享元对象可能被系统适当地共享
5、客户端(Client)角色
本角色需要维护一个对所有享元对象的引用。本角色需要自行存储所有享元对象的外部状态
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其类图如下:
太easy了,实现代码如下:
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class="php" name="code"><?php /** * 抽象享元角色 */ abstract class Flyweight { abstract public function operation( $state ); } /** * 具体享元角色 */ class ConcreteFlyweight extends Flyweight { private $_intrinsicState = null; public function __construct( $state ) { $this->_intrinsicState = $state; } public function operation( $state ) { echo 'ConcreteFlyweight operation, Intrinsic State = ' . $this->_intrinsicState. ' Extrinsic State = ' . $state . "\n"; } } /** * 不共享的具体享元,客户端直接调用 */ class UnsharedConcreteFlyweight extends Flyweight { private $_intrinsicState = null; public function __construct( $state ) { $this->_intrinsicState = $state; } public function operation( $state ) { echo 'UnsharedConcreteFlyweight operation, Intrinsic State = ' . $this->_intrinsicState. ' Extrinsic State = ' . $state . "\n"; } } /** * 享元工厂角色 */ class FlyweightFactory { private $_flyweights; public function __construct() { $this->_flyweights = array(); } public function getFlyweigth( $state ) { if ( isset( $this->_flyweights[$state] ) ) { return $this->_flyweights[$state]; } else { return $this->_flyweights[$state] = new ConcreteFlyweight( $state ); } } } $flyweightFactory = new FlyweightFactory(); $flyweight = $flyweightFactory->getFlyweigth( 'state A' ); $flyweight->operation( 'other state A' ); $flyweight = $flyweightFactory->getFlyweigth( 'state B' ); $flyweight->operation( 'other state B' ); /* 不共享的对象,单独调用 */ $uflyweight = new UnsharedConcreteFlyweight( 'state A' ); $uflyweight->operation( 'other state A' ); ?> 运行结果: ConcreteFlyweight operation, Intrinsic State = state A Extrinsic State = other state A ConcreteFlyweight operation, Intrinsic State = state B Extrinsic State = other state B UnsharedConcreteFlyweight operation, Intrinsic State = state A Extrinsic State = other state A [Finished in 0.3s]
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享元模式的优点
享元模式可以大大减少应用程序创建的对象,降低程序内存的占用,增强程序的性能,但它同时也提高了系统的复杂性,需要分离出外部状态和内部状态,而且外部状态具有固化特性,不应该随内部状态改变而改变,否则导致系统的逻辑混乱。
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享元模式的使用场景
1、系统中存在大量的相似对象
2、细粒度的对象都具备较接近的外部状态,而且内部状态与环境无关,也就是说对象没有特定身份。
3、需要缓冲池的场景
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享元模式的扩展
2、Composite模式
复合享元模式实际上是单纯享元模式与合成模式的组合。单纯享元对象可以作为树叶对象来讲,是可以共享的,而复合享元对象可以作为树枝对象,因此在复合享元角色中可以添加聚集管理方法
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<?php abstract class Flyweight { abstract public function operation( $state ); } /** * * 具体享元角色 */ class ConcreteFlyweight extends Flyweight { private $_intrinsicState = null; public function __construct( $state ) { $this->_intrinsicState = $state; } public function operation( $state ) { echo 'ConcreteFlyweight operation, Intrinsic State = ' . $this->_intrinsicState . ' Extrinsic State = ' . $state . "\n"; } } /** * * 不共享的具体享元,客户端直接调用 */ class UnsharedConcreteFlyweight extends Flyweight { private $_flyweights; public function __construct() { $this->_flyweights = array(); } public function operation( $state ) { foreach ( $this->_flyweights as $flyweight ) { $flyweight->operation( $state ); } } public function add( $state, Flyweight $flyweight ) { $this->_flyweights[$state] = $flyweight; } } /** * * 享元工厂角色 */ class FlyweightFactory { private $_flyweights; public function __construct() { $this->_flyweights = array(); } public function getFlyweigth( $state ) { if ( is_array( $state ) ) { // 复合模式 $uFlyweight = new UnsharedConcreteFlyweight(); foreach ( $state as $row ) { $uFlyweight->add( $row, $this->getFlyweigth( $row ) ); } return $uFlyweight; } else if ( is_string( $state ) ) { if ( isset( $this->_flyweights[$state] ) ) { return $this->_flyweights[$state]; } else { return $this->_flyweights[$state] = new ConcreteFlyweight( $state ); } } else { return null; } } } $flyweightFactory = new FlyweightFactory(); $flyweight = $flyweightFactory->getFlyweigth( 'state A' ); $flyweight->operation( 'other state A' ); $flyweight = $flyweightFactory->getFlyweigth( 'state B' ); $flyweight->operation( 'other state B' ); /* 复合对象*/ $uflyweight = $flyweightFactory->getFlyweigth( array( 'state A', 'state B' ) ); $uflyweight->operation( 'other state A' ); ?> 运行结果: ConcreteFlyweight operation, Intrinsic State = state A Extrinsic State = other state A ConcreteFlyweight operation, Intrinsic State = state B Extrinsic State = other state B ConcreteFlyweight operation, Intrinsic State = state A Extrinsic State = other state A ConcreteFlyweight operation, Intrinsic State = state B Extrinsic State = other state A [Finished in 0.2s]
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享元模式主要解决的是对象的共享问题,如何建立多个可共享的细粒度对象则是其关注的重点。