是什么导致了这个错误"Evaluator.java:6: error: cannot find symbol import org.antlr.v4.runtime.CharStreams;"？

Question

import java.io.*;
import org.antlr.v4.runtime.tree.*;
import org.antlr.v4.runtime.CharStream;
import org.antlr.v4.runtime.CharStreams;
import org.antlr.v4.runtime.CommonTokenStream;


public class Eval {

    public static void main(String[] args) {
        if (args.length != 1) {
            System.err.print("Usage: file");
        } else {
            String file = args[0];
            GrammarParser parser = getParser(file);
            ParseTree AbstractSynTree = parser.prog();
            AntlrToProgram programVisitor = new AntlrToProgram();
            Program prg = programVisitor.visit(AbstractSynTree);

        }

    }

    public static GrammarParser getParser(String file) {
        GrammarParser parser = null;
        try {
            CharStream input = CharStreams.fromFileName(file);
            GrammarLexer lexer = new GrammarLexer(input);
            CommonTokenStream tokens = new CommonTokenStream(lexer);
            parser = new GrammarParser(tokens);
        } catch (IOException e) {
            e.printStackTrace();
        }
        return parser;
    }
}

我一直收到错误：

Eval.java:6: error: cannot find symbol
import org.antlr.v4.runtime.CharStreams;
                           ^
  symbol:   class CharStreams
  location: package org.antlr.v4.runtime
Eval.java:29: error: cannot find symbol
            CharStream input = CharStreams.fromFileName(file);
                               ^
  symbol:   variable CharStreams
  location: class Eval
2 errors

同时编译Eval.java。我不确定发生了什么，因为所有其他Antlr类都被导入了，所以我假设类路径已经正确导入了。非常感谢您的帮助，谢谢！

Answer 1

查看CharStreams的源代码，您可以看到它是在ANTLR4.7中引入的。您最有可能使用的是低于该版本的ANTLR。