@Override
		public void enterEveryRule(ParserRuleContext ctx) {
			System.out.println("enter   " + getRuleNames()[ctx.getRuleIndex()] +
							   ", LT(1)=" + _input.LT(1).getText());
		}
This is all the parsing support code essentially; most of it is error recovery stuff.
runtime/Java/src/org/antlr/v4/runtime/Parser.java