php设计模式 Interpreter (解释器模式)

<?php
/**
 * 解释器 示例
 *
 * @create_date: 2010-01-04
 */
class Expression
{
    function interpreter($str)
    {
        return $str;
    }
}
 
class ExpressionNum extends Expression
{
    function interpreter($str)
    {
        switch($str)
        {
            case "0": return "零";
            case "1": return "一";
            case "2": return "二";
            case "3": return "三";
            case "4": return "四";
            case "5": return "五";
            case "6": return "六";
            case "7": return "七";
            case "8": return "八";
            case "9": return "九";
        }
    }
}
 
class ExpressionCharater extends Expression
{
    function interpreter($str)
    {
        return strtoupper($str);
    }
}
 
class Interpreter
{
    function execute($string)
    {
        $expression = null;
        for($i = 0;$i<strlen($string);$i++) {
            $temp = $string[$i];
            switch(true)
            {
               case is_numeric($temp): $expression = new ExpressionNum(); break;
               default: $expression = new ExpressionCharater();
            }
            echo $expression->interpreter($temp);
        }
    }
}
 
$obj = new Interpreter();
$obj->execute("12345abc");
?>