<?php

use a\cls_a;

    class add{
        public function getVal($n,$m){
            return $n + $m;
        }
    }

    class sub
    {
        public function getVal($n,$m)
        {
            return $n-$m;
        }
    }

    class mul
    {
        public function getVal($n,$m)
        {
            return $n * $m;
        }
    }

    class div
    {
        public function getVal($n,$m)
        {
            return $n / $m;
        }
    }

    //工程类:用来创建对象
    class mathOpt{
        public static function createObj($opt){
            switch ($opt)
            {
                case '+':
                    return new add();
                    break;
                case '-':
                    return new sub();
                    break;
                case '*':
                    return new mul();
                    break;
                case '/':
                    return new div();
                    break;
            }
        }
    }

    $obj = mathOpt::createObj('*');
    $ret=$obj  -> getVal(5,7);
    echo $ret;
?>