How to find only overridden methods in antlr4

I'm trying to find all overridden methods in java files using antlr4 with python runtime. I have taken the grammar from https://github.com/antlr/grammars-v4/tree/master/java. I'm able to find the methods using the below code successfully.

    istream = FileStream(repo_path, encoding='utf-8')
    lexer = JavaLexer(istream)
    stream = CommonTokenStream(lexer)
    parser = JavaParser(stream)
    tree = parser.compilationUnit()
    walker = ParseTreeWalker()
    walker.walk(PatternListener(), tree)

Inside Listener,

  def enterMethodDeclaration(self, ctx):
     method_name = ctx.IDENTIFIER().getText()
     method_defition = ctx.methodBody().getText()

Now I want to track only overridden methods, not all the methods. so, I made below changes.

In JavaLexer.g4,

OVERRIDEN           '@Override';

In JavaParser.g4,

methodDeclaration
    : OVERRIDEN typeTypeOrVoid IDENTIFIER formalParameters ('[' ']')*
      (THROWS qualifiedNameList)?
      methodBody
    ;

to restrict methodDeclaration to only overriden method, and I have re-generated all lexer and parser again. But this time I'm getting many mismatch issues while parsing, like below.

line 71:15 extraneous input 'void' expecting {<EOF>, 'abstract', 'boolean', 'byte', 'char', 'class', 'double', 'enum', 'final', 'float', 'int', 'interface', 'long', 'native', 'private', 'protected', 'public', 'short', 'static', 'strictfp', 'synchronized', 'transient', 'volatile', '@Override', '{', '}', ';', '<', '@', IDENTIFIER}
line 74:23 mismatched input '(' expecting ';'

Can anyone please highlight the mistake which I'm doing here, is there any other way to implement this?. Any suggestions or discussions are appreciated. Thank you in advance:).

You've changed the grammar, so that all methods must have an @Override annotation. It looks like at least one of your methods doesn't have such an annotation though. Therefore your Java file no longer fits your grammar and you get a syntax error.

If you don't want to change, which files are syntactically valid, but only want to change which methods are handled by your listener, then you should change your listener - not your grammar. Specifically, you should check whether the classBodyDeclaration that your methodDeclaration belongs to (i.e. the methodDeclaration's grand parent) contains an annotation named @Override (and then just not do anything if it doesn't).