22、PHP设计模式 - 享元模式

享元模式

享元模式(Flyweight Pattern)：运用共享技术有效地支持大量细粒度对象的复用。系统只使用少量的对象，而这些对象都很相似，状态变化很小，可以实现对象的多次复用。由于享元模式要求能够共享的对象必须是细粒度对象，因此它又称为轻量级模式，它是一种对象结构型模式。

模式结构

享元模式包含如下角色：

• Flyweight: 抽象享元类
• ConcreteFlyweight: 具体享元类
• UnsharedConcreteFlyweight: 非共享具体享元类
• FlyweightFactory: 享元工厂类

结构图

PHP代码实现

<?php
/**
 * 享元模式
 */
abstract class Flyweight {
   
     
    abstract public function operation($state);
}

//具体享元角色
class ConcreteFlyweight extends Flyweight {
   
     
    private $state = null;
    public function __construct($state) {
   
     
        $this->state = $state;
    }
    public function operation($state) {
   
     
        var_dump('具体Flyweight:'.$state);
    }

}

//不共享的具体享元，客户端直接调用
class UnsharedConcreteFlyweight extends Flyweight {
   
     
    private $state = null;
    public function __construct($state) {
   
     
        $this->state = $state;
    }
    public function operation($state) {
   
     
        var_dump('不共享的具体Flyweight:'.$state);
    }
}

//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);
        }
    }
}

$f = new FlyweightFactory();
$a = $f->getFlyweigth('state A');
$a->operation("other state A");

$b = $f->getFlyweigth('state B');
$b->operation('other state B');

/* 不共享的对象，单独调用 */
$u = new UnsharedConcreteFlyweight('state A');
$u->operation('other state A');

运行结果

string '具体Flyweight:other state A' (length=29)
string '具体Flyweight:other state B' (length=29)
string '不共享的具体Flyweight:other state A' (length=41)