Calculator.jj

PARSER_BEGIN(Calculator)
package com.github.quxiucheng.parser.javacc.calc;

import java.io.* ;

public class Calculator {

    public Calculator(String expr) {
        this((Reader)(new StringReader(expr)));
    }

    public static void main(String[] args) throws Exception  {
       Calculator calc = new Calculator(args[0]);
       System.out.println(calc.calc());
    }
}

PARSER_END(Calculator)



// 忽律的字符
SKIP:{
    " "
    | "\t"
    | "\n"
    | "\r"
    | "\r\n"
}


// 关键字
TOKEN:{
    <ADD :"+">
    | <SUB :"-">
    | <MUL :"*">
    | <DIV :"/">
    | <NUMBER :
            <DIGITS>
            | <DIGITS> "." <DIGITS>
            | <DIGITS> "."
            | "." <DIGITS>
      >
    | <#DIGITS : (["0"-"9"])+ >
}

// 计算
double calc():
{
    Double value ;
    Double result = 0.0;
}
{
  result = term()
  // 加减
  (
      <ADD>
      value = term()
      {result += value;}
      |
      <SUB>
      value =term()
      {result -= value;}
  )*
  {return result;}
}

// 乘除
double term():
{
    double value;
    double result;
}
{
    result = getNumber()
    (
       <MUL>
        value = getNumber()
        {result *= value;}
       |
       <DIV>
       value = getNumber()
       {result /= value;}
    )*
    {return result;}

}

// 获取字符串
double getNumber():
{
    double number;
    Token t;
}
{
    t = <NUMBER>
    {number = Double.parseDouble(t.image);
    return number;}
}