簡單工廠模式

boring發表於2019-08-12
模式

普通初學者喜歡的寫法

例子：實現一個簡單計算器


class Program
{
    public $symbol;
    public $num1;
    public $num2;

    public function __construct($symbol, $num1, $num2)
    {
        $this->symbol = $symbol;
        $this->num1 = $num1;
        $this->num2 = $num2;
    }

    public function calculate()
    {
        switch ($this->symbol) {
            case '+':
                $result = $this->num1 + $this->num2;
                break;
            case '-':
                $result = $this->num1 - $this->num2;
                break;
            case '*':
                $result = $this->num1 * $this->num2;
                break;
            case '/':
                if ($this->num2 != 0) {
                    $result = $this->num1 / $this->num2;
                } else {
                    $result = "除數不能為0";
                }
                break;
            default:
                $result = "運算子錯誤";
        }

        return $result;
    }
}

$program = new Program('+', 1, 14);
$result = $program->calculate();
print_r($result);//15

在上面的程式碼中存在的缺點：
緊耦合，不易擴充套件，如果新增了一個平方根運算，卻需要讓加減乘除都來參與編譯，如果一不小心把加法運算改成了減法,那就麻煩了。

使用簡單工廠模式重新實現達到解耦的目的

將加減乘除解耦，每一個運算用單獨的類去寫，再用工廠模式例項化出合適的物件，透過多型返回計算器結果，後面如果再加一個平方根運算可以新增一個平方根的類，如果需要修改加法運算，那就只需要修改OperationAdd類。


class Operation
{
    public $num1;
    public $num2;
}

class OperationAdd extends Operation
{
    public function getResult()
    {
        $result = $this->num1 + $this->num2;
        return $result;
    }
}

class OperationSub extends Operation
{
    public function getResult()
    {
        $result = $this->num1 - $this->num2;
        return $result;
    }
}

class OperationMul extends Operation
{
    public function getResult()
    {
        $result = $this->num1 * $this->num2;
        return $result;
    }
}

class OperationDiv extends Operation
{
    public function getResult()
    {

        if ($this->num2 != 0) {
            $result = $this->num1 / $this->num2;
        } else {
            $result = "除數不能為0";
        }
        return $result;
    }
}

class OperationFactory
{
    public static function createOperate($symbol)
    {
        switch ($symbol) {//多型
            case '+':
                $result = new OperationAdd();
                break;
            case '-':
                $result = new OperationSub();
                break;
            case '*':
                $result = new OperationMul();
                break;
            case '/':
                $result = new OperationDiv();
                break;
            default:
                $result = NULL;
        }
        return $result;
    }
}

$operationFactory = OperationFactory::createOperate('+');
$operationFactory->num1 = 21;
$operationFactory->num2 = 11;

echo $operationFactory->getResult();//32
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