1 
     $number)) { 8             return $this->$number; 9         } else {10             echo "the two number name is '_numberA' and '_numberB'";11             exit();12         }13     }14 15     public function __set($number, $value) {16         if (isset($this->$number)) {17             $this->$number = (float) $value;18         } else {19             echo "the two number name is '_numberA' and '_numberB'";20             exit();21         }22     }23 24     abstract function get_result();25 }26 27 28 class Operation_add extends Operation {29     public function get_result() {30         $result = 0;31         $result = $this->_numberA + $this->_numberB;32         return $result;33     }34 }35 36 class Operation_sub extends Operation {37     public function get_result() {38         $result = 0;39         $result = $this->_numverA - $this->_numverB;40         return $result;41     }42 }43 44 class Operation_mul extends Operation {45     public function get_result() {46         $result = 0;47         $result = $this->_numberA * $this->_numberB;48         return $result;49     }50 }51 52 class Operation_div extends Operation {53     public function get_result() {54         $result = 0;55         if ($this->_numberB == 0) {56             throw new Exception('闄ゆ暟涓嶈兘涓?');57         }58         $result = $this->_numberA / $this->_numberB;59         return $result;60     }61 }62 63 64 class OperationFactory {65     public static function create_operate($operate) {66         $oper = null;67         switch ($operate) {68         case '+':69             $oper = new Operation_add();70             break;71         case '-':72             $oper = new Operation_sub();73             break;74         case '*':75             $oper = new Operation_mul();76             break;77         case '/':78             $oper = new Operation_div();79             break;80         }81         return $oper;82     }83 }84 85 86 $oper = OperationFactory::create_operate('/');87 $oper->_numberA = 10;88 $oper->_numberB = 20;89 echo $oper->get_result();

可维护、可复用、可扩展、灵活

 

关联： 当一个类‘知道’另一个类的时候，可以用关联（association）

聚合： 表示一种弱的‘拥有’关系，体现的是A对象可以包含B对象，但B对象不是A对象的一部分。

组合：是以一种强的拥有关系，体现了严格的部分和整体的关系，部分和整体的生命周期一样。