class UnderscoreKeywordValidator extends VisitorValidator {

    @Override
    public void visit(Name n, ProblemReporter arg) {
        validateIdentifier(n, n.getIdentifier(), arg);
        super.visit(n, arg);
    }

    @Override
    public void visit(SimpleName n, ProblemReporter arg) {
        validateIdentifier(n, n.getIdentifier(), arg);
        super.visit(n, arg);
    }

    private static void validateIdentifier(Node n, String id, ProblemReporter arg) {<FILL_FUNCTION_BODY>}
}

        if ("_".equals(id)) {
            arg.report(n, "'_' is a reserved keyword.");
        }
    
<methods>public non-sealed void <init>() ,public void accept(com.github.javaparser.ast.Node, com.github.javaparser.ast.validator.ProblemReporter) <variables>