public final DFA getDFA(int mode) {
		return decisionToDFA[mode];
	}
Add a new DFA state if there isn't one with this set of
		configurations already. This method also detects the first
		configuration containing an ATN rule stop state. Later, when
		traversing the DFA, we will know which rule to accept.
runtime/Java/src/org/antlr/v4/runtime/atn/LexerATNSimulator.java