策略模式

obj = $obj;	
	}
	public function getPrice( $count = 1){
		return $this->obj->exec( $count );
	}
}

$obj = new ExecOrder();
$obj->setObject( new Math() );
echo $obj->getPrice( 1 ) . PHP_EOL;
$obj->setObject( new English() );
echo $obj->getPrice( 2 ) . PHP_EOL;