# HG changeset patch
# User redestad
# Date 1511190101 -3600
#      Mon Nov 20 16:01:41 2017 +0100
# Node ID 15663ec3c162efac8c816af2a3af91eaabafe724
# Parent  4fab795915b645475a8ed94c46e2c9ae3f27409c
imported patch immu0

diff --git a/src/java.base/share/classes/java/util/ImmutableCollections.java b/src/java.base/share/classes/java/util/ImmutableCollections.java
--- a/src/java.base/share/classes/java/util/ImmutableCollections.java
+++ b/src/java.base/share/classes/java/util/ImmutableCollections.java
@@ -59,6 +59,8 @@
         SALT = (int)((nt >>> 32) ^ nt);
     }
 
+    private static final Object NULL = new Object();
+
     /** No instances. */
     private ImmutableCollections() { }
 
@@ -86,55 +88,25 @@
         @Override public void    sort(Comparator<? super E> c) { throw uoe(); }
     }
 
-    static final class List0<E> extends AbstractImmutableList<E> {
-        private static final List0<?> INSTANCE = new List0<>();
+    static final List<?> EMPTY_LIST = new ListN<>();
 
-        @SuppressWarnings("unchecked")
-        static <T> List0<T> instance() {
-            return (List0<T>) INSTANCE;
-        }
+    static final Set<?> EMPTY_SET = new SetN<>();
 
-        private List0() { }
+    static final Map<?,?> EMPTY_MAP = new MapN<>();
 
-        @Override
-        public int size() {
-            return 0;
-        }
+    @SuppressWarnings("unchecked")
+    static <T> List<T> emptyList() {
+        return (List<T>) EMPTY_LIST;
+    }
 
-        @Override
-        public E get(int index) {
-            Objects.checkIndex(index, 0); // always throws IndexOutOfBoundsException
-            return null;                  // but the compiler doesn't know this
-        }
+    @SuppressWarnings("unchecked")
+    static <T> Set<T> emptySet() {
+        return (Set<T>) EMPTY_SET;
+    }
 
-        @Override
-        public Iterator<E> iterator() {
-            return Collections.emptyIterator();
-        }
-
-        private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
-            throw new InvalidObjectException("not serial proxy");
-        }
-
-        private Object writeReplace() {
-            return new CollSer(CollSer.IMM_LIST);
-        }
-
-        @Override
-        public boolean contains(Object o) {
-            Objects.requireNonNull(o);
-            return false;
-        }
-
-        @Override
-        public boolean containsAll(Collection<?> o) {
-            return o.isEmpty(); // implicit nullcheck of o
-        }
-
-        @Override
-        public int hashCode() {
-            return 1;
-        }
+    @SuppressWarnings("unchecked")
+    static <K,V> Map<K,V> emptyMap() {
+        return (Map<K,V>) EMPTY_MAP;
     }
 
     static final class List1<E> extends AbstractImmutableList<E> {
@@ -175,52 +147,6 @@
         }
     }
 
-    static final class List2<E> extends AbstractImmutableList<E> {
-        @Stable
-        private final E e0;
-        @Stable
-        private final E e1;
-
-        List2(E e0, E e1) {
-            this.e0 = Objects.requireNonNull(e0);
-            this.e1 = Objects.requireNonNull(e1);
-        }
-
-        @Override
-        public int size() {
-            return 2;
-        }
-
-        @Override
-        public E get(int index) {
-            Objects.checkIndex(index, 2);
-            if (index == 0) {
-                return e0;
-            } else { // index == 1
-                return e1;
-            }
-        }
-
-        @Override
-        public boolean contains(Object o) {
-            return o.equals(e0) || o.equals(e1); // implicit nullcheck of o
-        }
-
-        @Override
-        public int hashCode() {
-            int hash = 31 + e0.hashCode();
-            return 31 * hash + e1.hashCode();
-        }
-
-        private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
-            throw new InvalidObjectException("not serial proxy");
-        }
-
-        private Object writeReplace() {
-            return new CollSer(CollSer.IMM_LIST, e0, e1);
-        }
-    }
-
     static final class ListN<E> extends AbstractImmutableList<E> {
         @Stable
         private final E[] elements;
@@ -287,51 +213,6 @@
         @Override public boolean retainAll(Collection<?> c) { throw uoe(); }
     }
 
-    static final class Set0<E> extends AbstractImmutableSet<E> {
-        private static final Set0<?> INSTANCE = new Set0<>();
-
-        @SuppressWarnings("unchecked")
-        static <T> Set0<T> instance() {
-            return (Set0<T>) INSTANCE;
-        }
-
-        private Set0() { }
-
-        @Override
-        public int size() {
-            return 0;
-        }
-
-        @Override
-        public boolean contains(Object o) {
-            Objects.requireNonNull(o);
-            return false;
-        }
-
-        @Override
-        public boolean containsAll(Collection<?> o) {
-            return o.isEmpty(); // implicit nullcheck of o
-        }
-
-        @Override
-        public Iterator<E> iterator() {
-            return Collections.emptyIterator();
-        }
-
-        private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
-            throw new InvalidObjectException("not serial proxy");
-        }
-
-        private Object writeReplace() {
-            return new CollSer(CollSer.IMM_SET);
-        }
-
-        @Override
-        public int hashCode() {
-            return 0;
-        }
-    }
-
     static final class Set1<E> extends AbstractImmutableSet<E> {
         @Stable
         private final E e0;
@@ -369,75 +250,6 @@
         }
     }
 
-    static final class Set2<E> extends AbstractImmutableSet<E> {
-        @Stable
-        final E e0;
-        @Stable
-        final E e1;
-
-        Set2(E e0, E e1) {
-            if (e0.equals(Objects.requireNonNull(e1))) { // implicit nullcheck of e0
-                throw new IllegalArgumentException("duplicate element: " + e0);
-            }
-
-            if (SALT >= 0) {
-                this.e0 = e0;
-                this.e1 = e1;
-            } else {
-                this.e0 = e1;
-                this.e1 = e0;
-            }
-        }
-
-        @Override
-        public int size() {
-            return 2;
-        }
-
-        @Override
-        public boolean contains(Object o) {
-            return o.equals(e0) || o.equals(e1); // implicit nullcheck of o
-        }
-
-        @Override
-        public int hashCode() {
-            return e0.hashCode() + e1.hashCode();
-        }
-
-        @Override
-        public Iterator<E> iterator() {
-            return new Iterator<E>() {
-                private int idx = 0;
-
-                @Override
-                public boolean hasNext() {
-                    return idx < 2;
-                }
-
-                @Override
-                public E next() {
-                    if (idx == 0) {
-                        idx = 1;
-                        return e0;
-                    } else if (idx == 1) {
-                        idx = 2;
-                        return e1;
-                    } else {
-                        throw new NoSuchElementException();
-                    }
-                }
-            };
-        }
-
-        private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
-            throw new InvalidObjectException("not serial proxy");
-        }
-
-        private Object writeReplace() {
-            return new CollSer(CollSer.IMM_SET, e0, e1);
-        }
-    }
-
     /**
      * An array-based Set implementation. The element array must be strictly
      * larger than the size (the number of contained elements) so that at
@@ -474,7 +286,8 @@
 
         @Override
         public boolean contains(Object o) {
-            return probe(o) >= 0; // implicit nullcheck of o
+            Objects.requireNonNull(0);
+            return size > 0 && probe(o) >= 0; // implicit nullcheck of o
         }
 
         @Override
@@ -565,47 +378,6 @@
         @Override public void replaceAll(BiFunction<? super K,? super V,? extends V> f) { throw uoe(); }
     }
 
-    static final class Map0<K,V> extends AbstractImmutableMap<K,V> {
-        private static final Map0<?,?> INSTANCE = new Map0<>();
-
-        @SuppressWarnings("unchecked")
-        static <K,V> Map0<K,V> instance() {
-            return (Map0<K,V>) INSTANCE;
-        }
-
-        private Map0() { }
-
-        @Override
-        public Set<Map.Entry<K,V>> entrySet() {
-            return Set.of();
-        }
-
-        @Override
-        public boolean containsKey(Object o) {
-            Objects.requireNonNull(o);
-            return false;
-        }
-
-        @Override
-        public boolean containsValue(Object o) {
-            Objects.requireNonNull(o);
-            return false;
-        }
-
-        private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
-            throw new InvalidObjectException("not serial proxy");
-        }
-
-        private Object writeReplace() {
-            return new CollSer(CollSer.IMM_MAP);
-        }
-
-        @Override
-        public int hashCode() {
-            return 0;
-        }
-    }
-
     static final class Map1<K,V> extends AbstractImmutableMap<K,V> {
         @Stable
         private final K k0;
@@ -658,7 +430,6 @@
     static final class MapN<K,V> extends AbstractImmutableMap<K,V> {
         @Stable
         final Object[] table; // pairs of key, value
-        @Stable
         final int size; // number of pairs
 
         MapN(Object... input) {
@@ -689,7 +460,8 @@
 
         @Override
         public boolean containsKey(Object o) {
-            return probe(o) >= 0; // implicit nullcheck of o
+            Objects.requireNonNull(0);
+            return size > 0 && probe(o) >= 0;
         }
 
         @Override
@@ -718,6 +490,9 @@
         @Override
         @SuppressWarnings("unchecked")
         public V get(Object o) {
+            if (size == 0) {
+                return null;
+            }
             int i = probe(o);
             if (i >= 0) {
                 return (V)table[i+1];
@@ -948,7 +723,7 @@
                     return Set.of(array);
                 case IMM_MAP:
                     if (array.length == 0) {
-                        return ImmutableCollections.Map0.instance();
+                        return ImmutableCollections.emptyMap();
                     } else if (array.length == 2) {
                         return new ImmutableCollections.Map1<>(array[0], array[1]);
                     } else {
diff --git a/src/java.base/share/classes/java/util/List.java b/src/java.base/share/classes/java/util/List.java
--- a/src/java.base/share/classes/java/util/List.java
+++ b/src/java.base/share/classes/java/util/List.java
@@ -787,7 +787,7 @@
      * @since 9
      */
     static <E> List<E> of() {
-        return ImmutableCollections.List0.instance();
+        return ImmutableCollections.emptyList();
     }
 
     /**
@@ -820,7 +820,7 @@
      * @since 9
      */
     static <E> List<E> of(E e1, E e2) {
-        return new ImmutableCollections.List2<>(e1, e2);
+        return new ImmutableCollections.ListN<>(e1, e2);
     }
 
     /**
@@ -1030,11 +1030,9 @@
     static <E> List<E> of(E... elements) {
         switch (elements.length) { // implicit null check of elements
             case 0:
-                return ImmutableCollections.List0.instance();
+                return ImmutableCollections.emptyList();
             case 1:
                 return new ImmutableCollections.List1<>(elements[0]);
-            case 2:
-                return new ImmutableCollections.List2<>(elements[0], elements[1]);
             default:
                 return new ImmutableCollections.ListN<>(elements);
         }
diff --git a/src/java.base/share/classes/java/util/Map.java b/src/java.base/share/classes/java/util/Map.java
--- a/src/java.base/share/classes/java/util/Map.java
+++ b/src/java.base/share/classes/java/util/Map.java
@@ -1286,7 +1286,7 @@
      * @since 9
      */
     static <K, V> Map<K, V> of() {
-        return ImmutableCollections.Map0.instance();
+        return ImmutableCollections.emptyMap();
     }
 
     /**
@@ -1603,7 +1603,7 @@
     @SuppressWarnings("varargs")
     static <K, V> Map<K, V> ofEntries(Entry<? extends K, ? extends V>... entries) {
         if (entries.length == 0) { // implicit null check of entries
-            return ImmutableCollections.Map0.instance();
+            return ImmutableCollections.emptyMap();
         } else if (entries.length == 1) {
             return new ImmutableCollections.Map1<>(entries[0].getKey(),
                                                    entries[0].getValue());
diff --git a/src/java.base/share/classes/java/util/Set.java b/src/java.base/share/classes/java/util/Set.java
--- a/src/java.base/share/classes/java/util/Set.java
+++ b/src/java.base/share/classes/java/util/Set.java
@@ -448,7 +448,7 @@
      * @since 9
      */
     static <E> Set<E> of() {
-        return ImmutableCollections.Set0.instance();
+        return ImmutableCollections.emptySet();
     }
 
     /**
@@ -480,7 +480,7 @@
      * @since 9
      */
     static <E> Set<E> of(E e1, E e2) {
-        return new ImmutableCollections.Set2<>(e1, e2);
+        return new ImmutableCollections.SetN<>(e1, e2);
     }
 
     /**
@@ -691,11 +691,9 @@
     static <E> Set<E> of(E... elements) {
         switch (elements.length) { // implicit null check of elements
             case 0:
-                return ImmutableCollections.Set0.instance();
+                return ImmutableCollections.emptySet();
             case 1:
                 return new ImmutableCollections.Set1<>(elements[0]);
-            case 2:
-                return new ImmutableCollections.Set2<>(elements[0], elements[1]);
             default:
                 return new ImmutableCollections.SetN<>(elements);
         }