a few tweaks/comments.

runtime/Java/src/org/antlr/v4/runtime/atn/ATNConfig.java

@@ -75,6 +75,14 @@ public class ATNConfig {
 		return true;
 	}
 
+	/** Lexer non-greedy implementations need to track information per
+	 *  ATNConfig. When the lexer reaches an accept state for a lexer
+	 *  rule, it needs to wipe out any configurations associated with
+	 *  that rule that are part of a non-greedy subrule. To do that it
+	 *  has to make sure that it tracks when a configuration was derived
+	 *  from an element within a non-greedy subrule. We use depth for
+	 *  that. We're greedy when the depth is 0.
+	 */
 	public int getNonGreedyDepth() {
 		return 0;
 	}

runtime/Java/src/org/antlr/v4/runtime/atn/LexerATNSimulator.java

@@ -444,7 +444,7 @@ public class LexerATNSimulator extends ATNSimulator {
 				}
 			}
 
-			if (!((LexerATNConfig)config).isGreedy()) {
+			if ( !config.isGreedy() ) {
 				assert !(config.state instanceof RuleStopState);
 				nonGreedyAlts.set(config.alt);
 			}
@@ -582,7 +582,7 @@ public class LexerATNSimulator extends ATNSimulator {
 				}
 			}
 
-			if ( config.context == null || config.context.hasEmpty() ) {
+			if ( config.context == null || config.context.hasEmptyPath() ) {
 				if (config.context == null || config.context.isEmpty()) {
 					configs.add(config);
 					return;

runtime/Java/src/org/antlr/v4/runtime/atn/PredictionContext.java

@@ -70,7 +70,7 @@ public abstract class PredictionContext implements Iterable<SingletonPredictionC
 		return this == EMPTY;
 	}
 
-	public boolean hasEmpty() {
+	public boolean hasEmptyPath() {
 		return getInvokingState(size() - 1) == EMPTY_INVOKING_STATE;
 	}