protected void reset() {
			index = -1;
			line = 0;
			charPos = -1;
			dfaState = null;
		}
When we hit an accept state in either the DFA or the ATN, we
 have to notify the character stream to start buffering characters
 via {@link IntStream#mark} and record the current state. The current sim state
 includes the current index into the input, the current line,
 and current character position in that line. Note that the Lexer is
 tracking the starting line and characterization of the token. These
 variables track the "state" of the simulator when it hits an accept state.

 <p>We track these variables separately for the DFA and ATN simulation
 because the DFA simulation often has to fail over to the ATN
 simulation. If the ATN simulation fails, we need the DFA to fall
 back to its previously accepted state, if any. If the ATN succeeds,
 then the ATN does the accept and the DFA simulator that invoked it
 can simply return the predicted token type.</p>
runtime/Java/src/org/antlr/v4/runtime/atn/LexerATNSimulator.java