简介

享元模式更常见的叫法是缓存或 cache，一个对象只创立一次，之后始终复用这一对象。

跟单例不同在于，单例是全局只有惟一一个对象，所有人一起用同一个对象，且该对象是提前预设好的，不能定制。

而享元则能够依据参数不同创立出不同的实例，不过实例一旦创立就只保留一份，之后再次创立雷同参数的实例则返回该对象，供所有援用的中央应用，援用方之间共享同一份享元实例的数据。

过程有点像定制化的单例模式。

角色

  • Flyweight 享元类

    定制化的业务实体，依据不同须要可能定制不同的享元类，但一旦创立出一个享元类，当前都复用这一个类

  • FlyweightFactory 享元工厂类

    用来创立和缓存享元实体的中央

类图

代码

class Flyweight{    private $sharedState;    public function __construct($sharedState)    {        $this->sharedState = $sharedState;    }    public function operation($uniqueState): void    {        $s = json_encode($this->sharedState);        $u = json_encode($uniqueState);        echo "Flyweight: Displaying shared ($s) and unique ($u) state.\n";    }}class FlyweightFactory{    private $flyweights = [];    public function __construct(array $initialFlyweights)    {        foreach ($initialFlyweights as $state) {            $this->flyweights[$this->getKey($state)] = new Flyweight($state);        }    }    private function getKey(array $state): string    {        ksort($state);        return implode("_", $state);    }    public function getFlyweight(array $sharedState): Flyweight    {        $key = $this->getKey($sharedState);        if (!isset($this->flyweights[$key])) {            echo "FlyweightFactory: Can't find a flyweight, creating new one.\n";            $this->flyweights[$key] = new Flyweight($sharedState);        } else {            echo "FlyweightFactory: Reusing existing flyweight.\n";        }        return $this->flyweights[$key];    }    public function listFlyweights(): void    {        $count = count($this->flyweights);        echo "\nFlyweightFactory: I have $count flyweights:\n";        foreach ($this->flyweights as $key => $flyweight) {            echo $key . "\n";        }    }}$factory = new FlyweightFactory([    ["Chevrolet", "Camaro2018", "pink"],    ["Mercedes Benz", "C300", "black"],    ["Mercedes Benz", "C500", "red"],    ["BMW", "M5", "red"],    ["BMW", "X6", "white"],]);$factory->listFlyweights();function addCarToPoliceDatabase(    FlyweightFactory $ff, $plates, $owner,    $brand, $model, $color) {    echo "\nClient: Adding a car to database.\n";    $flyweight = $ff->getFlyweight([$brand, $model, $color]);    $flyweight->operation([$plates, $owner]);}addCarToPoliceDatabase($factory,    "CL234IR",    "James Doe",    "BMW",    "M5",    "red");addCarToPoliceDatabase($factory,    "CL234IR",    "James Doe",    "BMW",    "X1",    "red");$factory->listFlyweights();

output:

FlyweightFactory: I have 5 flyweights:Chevrolet_Camaro2018_pinkMercedes Benz_C300_blackMercedes Benz_C500_redBMW_M5_redBMW_X6_whiteClient: Adding a car to database.FlyweightFactory: Reusing existing flyweight.Flyweight: Displaying shared (["BMW","M5","red"]) and unique (["CL234IR","James Doe"]) state.Client: Adding a car to database.FlyweightFactory: Can't find a flyweight, creating new one.Flyweight: Displaying shared (["BMW","X1","red"]) and unique (["CL234IR","James Doe"]) state.FlyweightFactory: I have 6 flyweights:Chevrolet_Camaro2018_pinkMercedes Benz_C300_blackMercedes Benz_C500_redBMW_M5_redBMW_X6_whiteBMW_X1_red

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