工厂模式关注于抽象类型时如何解决创建对象实例的问题，通过子类实例化具体的类。

UML类图

代码实现

VehicleInterface.php

<?php

namespace DesignPatterns\Creational\FactoryMethod;

interface VehicleInterface
{
    public function setColor(string $rgb);
}

CarMerecedes.php

<?php

namespace DesignPatterns\Creational\FactoryMethod;

class CarMercedes implements VehicleInterface
{
    /**
     * @var string
     */
    private $color;

    public function setColor(string $rgb)
    {
        $this->color = $rgb;
    }

    public function addAMGTuning()
    {
        // do additional tuning here
    }
}

CarFerrari.php

<?php

namespace DesignPatterns\Creational\FactoryMethod;

class CarFerrari implements VehicleInterface
{
    /**
     * @var string
     */
    private $color;

    public function setColor(string $rgb)
    {
        $this->color = $rgb;
    }
}

Bicycle.php

<?php

namespace DesignPatterns\Creational\FactoryMethod;

class CarMercedes implements VehicleInterface
{
    /**
     * @var string
     */
    private $color;

    public function setColor(string $rgb)
    {
        $this->color = $rgb;
    }

    public function addAMGTuning()
    {
        // do additional tuning here
    }
}

FactroyMethod.php

<?php

namespace DesignPatterns\Creational\FactoryMethod;

abstract class FactoryMethod
{
    const CHEAP = 'cheap';
    const FAST = 'fast';

    abstract protected function createVehicle(string $type): VehicleInterface;

    public function create(string $type): VehicleInterface
    {
        $obj = $this->createVehicle($type);
        $obj->setColor('black');

        return $obj;
    }
}

ItalianFactroy.php

<?php

namespace DesignPatterns\Creational\FactoryMethod;

class ItalianFactory extends FactoryMethod
{
    protected function createVehicle(string $type): VehicleInterface
    {
        switch ($type) {
            case parent::CHEAP:
                return new Bicycle();
            case parent::FAST:
                return new CarFerrari();
            default:
                throw new \InvalidArgumentException("$type is not a valid vehicle");
        }
    }
}

GermanFactroy.php

<?php

namespace DesignPatterns\Creational\FactoryMethod;

class GermanFactory extends FactoryMethod
{
    protected function createVehicle(string $type): VehicleInterface
    {
        switch ($type) {
            case parent::CHEAP:
                return new Bicycle();
            case parent::FAST:
                $carMercedes = new CarMercedes();
                // we can specialize the way we want some concrete Vehicle since we know the class
                $carMercedes->addAMGTuning();

                return $carMercedes;
            default:
                throw new \InvalidArgumentException("$type is not a valid vehicle");
        }
    }
}

FactroyMethodTest.php

<?php

namespace DesignPatterns\Creational\FactoryMethod\Tests;

use DesignPatterns\Creational\FactoryMethod\Bicycle;
use DesignPatterns\Creational\FactoryMethod\CarFerrari;
use DesignPatterns\Creational\FactoryMethod\CarMercedes;
use DesignPatterns\Creational\FactoryMethod\FactoryMethod;
use DesignPatterns\Creational\FactoryMethod\GermanFactory;
use DesignPatterns\Creational\FactoryMethod\ItalianFactory;
use PHPUnit\Framework\TestCase;

class FactoryMethodTest extends TestCase
{
    public function testCanCreateCheapVehicleInGermany()
    {
        $factory = new GermanFactory();
        $result = $factory->create(FactoryMethod::CHEAP);

        $this->assertInstanceOf(Bicycle::class, $result);
    }

    public function testCanCreateFastVehicleInGermany()
    {
        $factory = new GermanFactory();
        $result = $factory->create(FactoryMethod::FAST);

        $this->assertInstanceOf(CarMercedes::class, $result);
    }

    public function testCanCreateCheapVehicleInItaly()
    {
        $factory = new ItalianFactory();
        $result = $factory->create(FactoryMethod::CHEAP);

        $this->assertInstanceOf(Bicycle::class, $result);
    }

    public function testCanCreateFastVehicleInItaly()
    {
        $factory = new ItalianFactory();
        $result = $factory->create(FactoryMethod::FAST);

        $this->assertInstanceOf(CarFerrari::class, $result);
    }

    /**
     * @expectedException \InvalidArgumentException
     * @expectedExceptionMessage spaceship is not a valid vehicle
     */
    public function testUnknownType()
    {
        (new ItalianFactory())->create('spaceship');
    }
}

心得总结：

- 该模型有四种角色：抽象工厂、具体工厂、抽象产品、具体产品；具体工厂都是进行具体产品对象的实例；
- 工厂模型运行系统在不改变工厂角色和产品实现，再继续增加具体的工厂和具体的产品；