Code for Antlr problem

main.java

import org.antlr.v4.runtime.*;
import org.antlr.v4.runtime.tree.*;
import java.io.FileInputStream;
import java.io.InputStream;

public class Main {
        public static void main(String[] args) throws Exception {

                String expression = "hello parr";

                ANTLRInputStream input = new ANTLRInputStream(expression);
                PreParseLexer lexer = new PreParseLexer(input);
                CommonTokenStream tokens = new CommonTokenStream(lexer);
                PreParseParser parser = new PreParseParser(tokens);
                ParseTree tree = parser.r();

        }
}

PreParse.g4

grammar PreParse;
import PreParseLex;

r: 'hello' ID;

PreParseLex.g4

lexer grammar PreParseLex;

ID: [a-z]+;
WS: [ \t\r\n]+ -> skip ;

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
using Antlr4.Runtime;
using Antlr4.Runtime.Misc;
using Antlr4.Runtime.Tree;

namespace PreparseApp
{
    class Program
    {
        static void Main(string[] args)
        {
            string expression = "hello parr";
            AntlrInputStream input = new AntlrInputStream(expression);

            PreParseLex lexer = new PreParseLex(input);
            CommonTokenStream tokens = new CommonTokenStream(lexer);
            PreParseParser parser = new PreParseParser(tokens);
            IParseTree tree = parser.r();

            Console.WriteLine("Done");
        }
    }
}