purpose
In order to save memory usage, Flyweight mode will try to make similar objects share memory. This is necessary when a large number of similar objects are used. A common practice is to save the state of similar objects in an external data structure and pass them to the flyweight object when needed.
UML graphics
Code
- FlyweightInterface.php
<?php
namespace DesignPatterns\Structural\Flyweight;
/**
* 创建享元接口 FlyweightInterface 。
*/
interface FlyweightInterface
{
/**
* 创建传递函数。
* 返回字符串格式数据。
*/
public function render(string $extrinsicState): string;
}- CharacterFlyweight.php
<?php
namespace DesignPatterns\Structural\Flyweight;
/**
* 假如可以的话，实现享元接口并增加内存存储内部状态。
* 具体的享元实例被工厂类的方法共享。
*/
class CharacterFlyweight implements FlyweightInterface
{
/**
* 任何具体的享元对象存储的状态必须独立于其运行环境。
* 享元对象呈现的特点，往往就是对应的编码的特点。
*
* @var string
*/
private $name;
/**
* 输入一个字符串对象 $name。
*/
public function __construct(string $name)
{
$this->name = $name;
}
/**
* 实现 FlyweightInterface 中的传递方法 render() 。
*/
public function render(string $font): string
{
// 享元对象需要客户端提供环境依赖信息来自我定制。
// 外在状态经常包含享元对象呈现的特点，例如字符。
return sprintf('Character %s with font %s', $this->name, $font);
}
}- FlyweightFactory.php
<?php
namespace DesignPatterns\Structural\Flyweight;
/**
* 工厂类会管理分享享元类，客户端不应该直接将他们实例化。
* 但可以让工厂类负责返回现有的对象或创建新的对象。
*/
class FlyweightFactory implements \Countable
{
/**
* @var CharacterFlyweight[]
* 定义享元特征数组。
* 用于存储不同的享元特征。
*/
private $pool = [];
/**
* 输入字符串格式数据 $name。
* 返回 CharacterFlyweight 对象。
*/
public function get(string $name): CharacterFlyweight
{
if (!isset($this->pool[$name])) {
$this->pool[$name] = new CharacterFlyweight($name);
}
return $this->pool[$name];
}
/**
* 返回享元特征个数。
*/
public function count(): int
{
return count($this->pool);
}
}test
- Tests/FlyweightTest.php
<?php
namespace DesignPatterns\Structural\Flyweight\Tests;
use DesignPatterns\Structural\Flyweight\FlyweightFactory;
use PHPUnit\Framework\TestCase;
/**
* 创建自动化测试单元 FlyweightTest 。
*/
class FlyweightTest extends TestCase
{
private $characters = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k',
'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'];
private $fonts = ['Arial', 'Times New Roman', 'Verdana', 'Helvetica'];
public function testFlyweight()
{
$factory = new FlyweightFactory();
foreach ($this->characters as $char) {
foreach ($this->fonts as $font) {
$flyweight = $factory->get($char);
$rendered = $flyweight->render($font);
$this->assertEquals(sprintf('Character %s with font %s', $char, $font), $rendered);
}
}
// 享元模式会保证实例被分享。
// 相比拥有成百上千的私有对象，
// 必须要有一个实例代表所有被重复使用来显示不同单词的字符。
$this->assertCount(count($this->characters), $factory);
}
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