public List<Token> getTokens(int start, int stop, int ttype) {
		HashSet<Integer> s = new HashSet<Integer>(ttype);
		s.add(ttype);
		return getTokens(start,stop, s);
    }
Given a start and stop index, return a List of all tokens in
 the token type BitSet.  Return null if no tokens were found.  This
 method looks at both on and off channel tokens.
runtime/Java/src/org/antlr/v4/runtime/BufferedTokenStream.java