Read in and parse a file to be able to set variables

Question

I am trying to use javacc to achieve/perform a few operations. For now, I want to read in a file that would look something like:

a is 6
b is 5
+

My program should then be able to parse this file and create/assign two variables a and b with the above values. It would then sum these two values as the third line in the file is a +

Right now, I have a program that can perform basic arithmetic like so:

PARSER_BEGIN(Evaluator)

public class Evaluator {
    public static void main(String[] args) throws Exception {
        int result = new Evaluator(new java.io.StringReader(args[0])).S();
        System.out.println(result);
    }
}

PARSER_END(Evaluator)

SKIP:  { " " | "\t" | "\n" | "\r"                    }
TOKEN: { "(" | ")" | "+" | "-" | "*" | "/" | <NUM: (["0"-"9"])+> }

int S(): {int sum;}
{
  sum=E() <EOF> {return sum;}
}

int E(): {int sum, x;}
{
  sum=T() ("+" x=T() {sum += x;} )* {return sum;}
}

int T(): {int sum, x;}
{
  sum=F() ("*" x=F() {sum *= x;} )* {return sum;}
}

int F(): {int x; Token n;}
{
  n=<NUM> {return Integer.parseInt(n.image);}
|
  "(" x=E() ")" {return x;}
}

To use the above, you would create a Grammar file MyFile.jj and run javacc MyFile.jj - this would then generate the relevant Java classes. Then running javac *.java would compile them and finally, you can then run java Evaluator 2+3 which would then outpt 5.

In Java, I know you can read in a file by using the Scanner class and running java MyClass < file.txt

So with the above, I have the following:

PARSER_BEGIN(FileParser)

import java.util.Scanner;
import java.io.*;

public class FileParser {
    public static void main(String[] args) throws Exception {
//        int result = new Evaluator(new java.io.StringReader(args[0])).Start();
//        System.out.println(result);

        Scanner scanner = new Scanner(System.in);

        // Read input from the console using Scanner
        StringBuilder inputBuilder = new StringBuilder();
        while (scanner.hasNextLine()) {
          String line = scanner.nextLine();
          inputBuilder.append(line).append("\n");
        }

        // Pass the input string to the parser
        String input = inputBuilder.toString();

        try {
          FileParser parser = new FileParser(new ByteArrayInputStream(input.getBytes()));
          parser.Start();
        } catch (ParseException e) {
          e.printStackTrace();
        }
    }
}

PARSER_END(FileParser)

SKIP:  { " " | "\t" | "\r" }
//TOKEN: { "(" | ")" | "+" | "-" | "*" | "/" | <NUMBER: (["0"-"9"])+> | <IDENTIFIER: ["a"-"z"] ["a"-"z"] > | <EOL: "\n" > }
TOKEN: {
  <IDENTIFIER: (["a"-"z"] ["a"-"z"])* > |
  <NUMBER: (["0"-"9"])+ > |
  <ASSIGN: "is" > |
  <EOL: "\n" >
}

int Start(): {int sum;}
{
//  sum = Expression() <EOF> { return sum; }
    Assignment()
    Assignment()
    Expression()
}

void Assignment(): {int a, b;}
{
  <IDENTIFIER> "is" <NUMBER> <EOL>
  {
    String variableName = ((Token)jjtGetChild(0)).image;
    int value = Integer.parseInt(((Token)jjtGetChild(2)).image);
    if (variableName.equals("a")) {
      a = value;
    } else if (variableName.equals("b")) {
      b = value;
    }
  }
}


int Expression(): {int a, b;}
{
//  sum = Term() ("+" x = Term() { sum += x; })* { return sum; }
    "+"
    {
        int result = a + b;
        System.out.println("Sum of a and b: " + result);

    }
}

int Term(): {int product, factor;}
{
  product = Factor() ("*" factor = Factor() { product *= factor; })* { return product; }
}

int Factor(): {int value; Token numToken;}
{
  numToken = <NUMBER> { return Integer.parseInt(numToken.image); }
  |
  "(" value = Expression() ")" { return value; }
}

This compiles fine with javacc however when I go to compile the Java classes I get the following:

FileParser.java:43: error: cannot find symbol
    String variableName = ((Token)jjtGetChild(0)).image;
                                  ^
  symbol:   method jjtGetChild(int)
  location: class FileParser
FileParser.java:44: error: cannot find symbol
    int value = Integer.parseInt(((Token)jjtGetChild(2)).image);
                                         ^
  symbol:   method jjtGetChild(int)
  location: class FileParser

I have not been able to find much on this online. How can I fix this?