Java找不到ANTLR符号ParserRuleContext和RContext

Question

我正在尝试使用ANTLR4进行项目，并且正在关注此tutorial和此question。

以下是我的Drink.java文件

import org.antlr.v4.runtime.*;
import org.antlr.v4.runtime.tree.*;
import static org.antlr.v4.runtime.CharStreams.fromFileName;

public class Drink {

public static void main (String [] args) {
            CharStream cs = fromFileName("test.txt");  //load the file

            DrinkLexer lexer = new DrinkLexer(cs);  //instantiate a lexer
            CommonTokenStream tokens = new CommonTokenStream(lexer); //scan stream for tokens
            DrinkParser parser = new DrinkParser(tokens);  //parse the tokens

            ParseTree tree = parser.drinkSentence(); // parse the content and get the tree
            DrinkWalker listener = new DrinkWalker();

            ParseTreeWalker walker = new ParseTreeWalker();
            walker.walk(listener,tree);
    }
}

以下是我的DrinkWalker.java文件

public class DrinkWalker extends DrinkBaseListener {
    @Override public void enterEveryRule(ParserRuleContext ctx) {  
        System.out.println("rule entered: " + ctx.getText());//code that executes per rule
    }
    public void enterR(DrinkParser.RContext ctx ) {
            System.out.println( "Entering R : " + ctx.ID().getText() );
    }

    public void exitR(DrinkParser.RContext ctx ) {
            System.out.println( "Exiting R" );
    }
}

我手动编译它们，但出现以下错误：

Override public void enterEveryRule(ParserRuleContext ctx) {
                                         ^
symbol:   class ParserRuleContext
location: class DrinkWalker

DrinkWalker.java:5: error: cannot find symbol
    public void enterR(DrinkParser.RContext ctx ) {
                                  ^
symbol:   class RContext
location: class DrinkParser
DrinkWalker.java:9: error: cannot find symbol
    public void exitR(DrinkParser.RContext ctx ) {
                                 ^
symbol:   class RContext
location: class DrinkParser

上面提到的RContext和ParserRuleContext函数是什么？