问ANTRL4解析错误

EN

grammar Abc;

@header {
    package antlr4;
}

fragment DIGIT : [0-9]+;

log : DIGIT;

public class OwnParser extends AbcBaseListener
{


    public static void main(String args[])
    {
        String javaClassContent = "9";
        AbcLexer abcLexer = new AbcLexer(CharStreams.fromString(javaClassContent));

        CommonTokenStream tokens = new CommonTokenStream(abcLexer);
        AbcParser parser = new AbcParser(tokens);

         ParseTree tree = parser.log();

        ParseTreeWalker walker = new ParseTreeWalker();
        OwnParser listener= new OwnParser();

        walker.walk(listener, tree);
    }
}