简单工厂的异常，不知如何修改

<?php
//接口
interface calc{
   public function getResult();
}
//运算类
class Operation{
   protected $num1=0;
   protected $num2=0;
   protected $result=0;

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

//四则运算类
class OperAdd extends Operation implements calc{
   public function getResult(){
       return $this->result=$this->num1+$this->num2;
   }
}
class OperSub extends Operation implements calc{
   public function getResult(){
       return $this->result=$this->num1-$this->num2;
   }
}
class OperMul extends Operation implements calc{
   public function getResult(){
       return $this->result=$this->num1*$this->num2;
   }
}
class OperDiv extends Operation implements calc{
   public function getResult(){
       if(intval($this->num2)==0){
           return $this->result="被除数不能为‘0’！";
       }else{
           return $this->result=$this->num1/$this->num2;
       }
   }
}
class OperFactory{
   private static $obj;
   public static function createrOper($type){
       try {
           switch ($type){
               case'+';
                   self::$obj = new OperAdd();
                   break;
               case'-';
                   self::$obj = new OperSub();
                   break;
               case'*';
                   self::$obj = new OperMul();
                   break;
               case '/':
                   self::$obj = new OperDiv();
                   break;
                   default:
                       throw new Exception('unknow type');
               }
           } catch (Exception $e) {
               echo $e->getMessage();
       }
   }
}
$obj = OperFactory::createrOper('+');
$obj->setNum(2,2);
echo $obj->getResult();

问题在 $obj->setNum(2,2);总是找不到对象，实在是找不出来问题，求解。

phpcn_u7372829 hari yang lalu803

简单工厂的异常，不知如何修改

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