diff --git a/runtime/Java/src/org/antlr/v4/runtime/Lexer.java b/runtime/Java/src/org/antlr/v4/runtime/Lexer.java
index 34b2fe426..55322153c 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/Lexer.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/Lexer.java
@@ -29,9 +29,9 @@
 package org.antlr.v4.runtime;
 
 import org.antlr.v4.runtime.atn.LexerATNSimulator;
+import org.antlr.v4.runtime.misc.IntegerStack;
 import org.antlr.v4.runtime.misc.Interval;
 
-import java.util.ArrayDeque;
 import java.util.ArrayList;
 import java.util.EmptyStackException;
 import java.util.List;
@@ -91,7 +91,7 @@ public abstract class Lexer extends Recognizer<Integer, LexerATNSimulator>
 	/** The token type for the current token */
 	public int _type;
 
-	public ArrayDeque<Integer> _modeStack = new ArrayDeque<Integer>();
+	public final IntegerStack _modeStack = new IntegerStack();
 	public int _mode = Lexer.DEFAULT_MODE;
 
 	/** You can set the text for the current token to override what is in
diff --git a/runtime/Java/src/org/antlr/v4/runtime/misc/IntervalSet.java b/runtime/Java/src/org/antlr/v4/runtime/misc/IntervalSet.java
index dc1f25062..21dd7a271 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/misc/IntervalSet.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/misc/IntervalSet.java
@@ -530,6 +530,20 @@ public class IntervalSet implements IntSet {
 		return n;
     }
 
+	public IntegerList toIntegerList() {
+		IntegerList values = new IntegerList(size());
+		int n = intervals.size();
+		for (int i = 0; i < n; i++) {
+			Interval I = intervals.get(i);
+			int a = I.a;
+			int b = I.b;
+			for (int v=a; v<=b; v++) {
+				values.add(v);
+			}
+		}
+		return values;
+	}
+
     @Override
     public List<Integer> toList() {
 		List<Integer> values = new ArrayList<Integer>();
@@ -579,19 +593,7 @@ public class IntervalSet implements IntSet {
 	}
 
 	public int[] toArray() {
-		int[] values = new int[size()];
-		int n = intervals.size();
-		int j = 0;
-		for (int i = 0; i < n; i++) {
-			Interval I = intervals.get(i);
-			int a = I.a;
-			int b = I.b;
-			for (int v=a; v<=b; v++) {
-				values[j] = v;
-				j++;
-			}
-		}
-		return values;
+		return toIntegerList().toArray();
 	}
 
 	@Override