--- a/src/java.base/share/classes/java/util/ArrayDeque.java	Tue Jul 10 11:13:33 2018 -0400
+++ b/src/java.base/share/classes/java/util/ArrayDeque.java	Tue Jul 10 10:24:08 2018 -0700
@@ -180,7 +180,7 @@
      * sufficient to hold 16 elements.
      */
     public ArrayDeque() {
-        elements = new Object[16];
+        elements = new Object[16 + 1];
     }
 
     /**

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/jdk/java/util/ArrayDeque/WhiteBox.java	Tue Jul 10 10:24:08 2018 -0700
@@ -0,0 +1,153 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Martin Buchholz with assistance from members of JCP
+ * JSR-166 Expert Group and released to the public domain, as
+ * explained at http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+/*
+ * @test
+ * @modules java.base/java.util:open
+ * @run testng WhiteBox
+ * @summary White box tests of implementation details
+ */
+
+import static org.testng.Assert.*;
+import org.testng.annotations.Test;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.VarHandle;
+import java.util.ArrayDeque;
+import java.util.concurrent.ThreadLocalRandom;
+
+@Test
+public class WhiteBox {
+    final ThreadLocalRandom rnd = ThreadLocalRandom.current();
+    final VarHandle ELEMENTS, HEAD, TAIL;
+
+    WhiteBox() throws ReflectiveOperationException {
+        Class<?> klazz = ArrayDeque.class;
+        MethodHandles.Lookup lookup
+            = MethodHandles.privateLookupIn(klazz, MethodHandles.lookup());
+        ELEMENTS = lookup.findVarHandle(klazz, "elements", Object[].class);
+        HEAD = lookup.findVarHandle(klazz, "head", int.class);
+        TAIL = lookup.findVarHandle(klazz, "tail", int.class);
+    }
+
+    Object[] elements(ArrayDeque d) { return (Object[]) ELEMENTS.get(d); }
+    int head(ArrayDeque d) { return (int) HEAD.get(d); }
+    int tail(ArrayDeque d) { return (int) TAIL.get(d); }
+
+    void checkCapacity(ArrayDeque d, int capacity) {
+        assertTrue(d.isEmpty());
+        assertEquals(0, head(d));
+        assertEquals(0, tail(d));
+        Object[] initialElements = elements(d);
+
+        assertInvariants(d);
+        for (int i = capacity; i--> 0; ) {
+            d.add(rnd.nextInt(42));
+            assertSame(elements(d), initialElements);
+            assertInvariants(d);
+        }
+
+        d.add(rnd.nextInt(42));
+        assertNotSame(elements(d), initialElements);
+        assertInvariants(d);
+    }
+
+    @Test
+    public void defaultConstructor() {
+        checkCapacity(new ArrayDeque(), 16);
+    }
+
+    @Test
+    public void shouldNotResizeWhenInitialCapacityProvided() {
+        int initialCapacity = rnd.nextInt(20);
+        checkCapacity(new ArrayDeque(initialCapacity), initialCapacity);
+    }
+
+    byte[] serialBytes(Object o) {
+        try {
+            ByteArrayOutputStream bos = new ByteArrayOutputStream();
+            ObjectOutputStream oos = new ObjectOutputStream(bos);
+            oos.writeObject(o);
+            oos.flush();
+            oos.close();
+            return bos.toByteArray();
+        } catch (Exception fail) {
+            throw new AssertionError(fail);
+        }
+    }
+
+    @SuppressWarnings("unchecked")
+    <T> T serialClone(T o) {
+        try {
+            ObjectInputStream ois = new ObjectInputStream
+                (new ByteArrayInputStream(serialBytes(o)));
+            T clone = (T) ois.readObject();
+            assertNotSame(o, clone);
+            assertSame(o.getClass(), clone.getClass());
+            return clone;
+        } catch (Exception fail) {
+            throw new AssertionError(fail);
+        }
+    }
+
+    @Test
+    public void testSerialization() {
+        ArrayDeque[] ds = { new ArrayDeque(), new ArrayDeque(rnd.nextInt(20)) };
+        for (ArrayDeque d : ds) {
+            if (rnd.nextBoolean()) d.add(99);
+            ArrayDeque clone = serialClone(d);
+            assertInvariants(clone);
+            assertNotSame(elements(d), elements(clone));
+            assertEquals(d, clone);
+        }
+    }
+
+    /** Checks conditions which should always be true. */
+    void assertInvariants(ArrayDeque d) {
+        final Object[] elements = elements(d);
+        final int head = head(d);
+        final int tail = tail(d);
+        final int capacity = elements.length;
+        assertTrue(0 <= head && head < capacity);
+        assertTrue(0 <= tail && tail < capacity);
+        assertTrue(capacity > 0);
+        assertTrue(d.size() < capacity);
+        assertTrue((head == tail) ^ (elements[head] != null));
+        assertNull(elements[tail]);
+        assertTrue((head == tail) ^ (elements[Math.floorMod(tail - 1, capacity)] != null));
+    }
+}