設計模式-簡單工廠模式

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 = "除數不能爲0";
                }
                break;
            default:
                $result = "運算符錯誤";
        }

        return $result;
    }
}

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

在上面的代碼中存在的缺點： 緊耦合，不易擴展，若是新增了一個平方根運算，卻須要讓加減乘除都來參與編譯，若是一不當心把加法運算改爲了減法,那就麻煩了。

使用簡單工廠模式從新實現達到解耦的目的

將加減乘除解耦，每個運算用單獨的類去寫，再用工廠模式實例化出合適的對象，經過多態返回計算器結果，後面若是再加一個平方根運算能夠新增一個平方根的類，若是須要修改加法運算，那就只須要修改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 = "除數不能爲0";
        }
        return $result;
    }
}

class OperationFactory {
    public static function createOperate($symbol) {
        switch ($symbol) {//多態
            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
複製代碼