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src/java.base/share/classes/java/util/Set.java

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rev 17661 : 8177290: add copy factory methods for unmodifiable List, Set, Map
8184690: add Collectors for collecting into unmodifiable List, Set, and Map
Reviewed-by: XXX

@@ -61,19 +61,20 @@
  * the insertion of an ineligible element into the set may throw an
  * exception or it may succeed, at the option of the implementation.
  * Such exceptions are marked as "optional" in the specification for this
  * interface.
  *
- * <h2><a id="immutable">Immutable Set Static Factory Methods</a></h2>
- * <p>The {@link Set#of(Object...) Set.of()} static factory methods
- * provide a convenient way to create immutable sets. The {@code Set}
+ * <h2><a id="unmodifiable">Unmodifiable Sets</a></h2>
+ * <p>The {@link Set#of(Object...) Set.of} and
+ * {@link Set#copyOf Set.copyOf} static factory methods
+ * provide a convenient way to create unmodifiable sets. The {@code Set}
  * instances created by these methods have the following characteristics:
  *
  * <ul>
- * <li>They are <em>structurally immutable</em>. Elements cannot be added or
- * removed. Calling any mutator method will always cause
- * {@code UnsupportedOperationException} to be thrown.
+ * <li>They are <a href="Collection.html#unmodifiable"><i>unmodifiable</i></a>. Elements cannot
+ * be added or removed. Calling any mutator method on the Set
+ * will always cause {@code UnsupportedOperationException} to be thrown.
  * However, if the contained elements are themselves mutable, this may cause the
  * Set to behave inconsistently or its contents to appear to change.
  * <li>They disallow {@code null} elements. Attempts to create them with
  * {@code null} elements result in {@code NullPointerException}.
  * <li>They are serializable if all elements are serializable.

@@ -437,12 +438,12 @@
     default Spliterator<E> spliterator() {
         return Spliterators.spliterator(this, Spliterator.DISTINCT);
     }
 
     /**
-     * Returns an immutable set containing zero elements.
-     * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+     * Returns an unmodifiable set containing zero elements.
+     * See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
      *
      * @param <E> the {@code Set}'s element type
      * @return an empty {@code Set}
      *
      * @since 9

@@ -450,12 +451,12 @@
     static <E> Set<E> of() {
         return ImmutableCollections.Set0.instance();
     }
 
     /**
-     * Returns an immutable set containing one element.
-     * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+     * Returns an unmodifiable set containing one element.
+     * See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
      *
      * @param <E> the {@code Set}'s element type
      * @param e1 the single element
      * @return a {@code Set} containing the specified element
      * @throws NullPointerException if the element is {@code null}

@@ -465,12 +466,12 @@
     static <E> Set<E> of(E e1) {
         return new ImmutableCollections.Set1<>(e1);
     }
 
     /**
-     * Returns an immutable set containing two elements.
-     * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+     * Returns an unmodifiable set containing two elements.
+     * See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
      *
      * @param <E> the {@code Set}'s element type
      * @param e1 the first element
      * @param e2 the second element
      * @return a {@code Set} containing the specified elements

@@ -482,12 +483,12 @@
     static <E> Set<E> of(E e1, E e2) {
         return new ImmutableCollections.Set2<>(e1, e2);
     }
 
     /**
-     * Returns an immutable set containing three elements.
-     * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+     * Returns an unmodifiable set containing three elements.
+     * See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
      *
      * @param <E> the {@code Set}'s element type
      * @param e1 the first element
      * @param e2 the second element
      * @param e3 the third element

@@ -500,12 +501,12 @@
     static <E> Set<E> of(E e1, E e2, E e3) {
         return new ImmutableCollections.SetN<>(e1, e2, e3);
     }
 
     /**
-     * Returns an immutable set containing four elements.
-     * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+     * Returns an unmodifiable set containing four elements.
+     * See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
      *
      * @param <E> the {@code Set}'s element type
      * @param e1 the first element
      * @param e2 the second element
      * @param e3 the third element

@@ -519,12 +520,12 @@
     static <E> Set<E> of(E e1, E e2, E e3, E e4) {
         return new ImmutableCollections.SetN<>(e1, e2, e3, e4);
     }
 
     /**
-     * Returns an immutable set containing five elements.
-     * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+     * Returns an unmodifiable set containing five elements.
+     * See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
      *
      * @param <E> the {@code Set}'s element type
      * @param e1 the first element
      * @param e2 the second element
      * @param e3 the third element

@@ -539,12 +540,12 @@
     static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5) {
         return new ImmutableCollections.SetN<>(e1, e2, e3, e4, e5);
     }
 
     /**
-     * Returns an immutable set containing six elements.
-     * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+     * Returns an unmodifiable set containing six elements.
+     * See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
      *
      * @param <E> the {@code Set}'s element type
      * @param e1 the first element
      * @param e2 the second element
      * @param e3 the third element

@@ -561,12 +562,12 @@
         return new ImmutableCollections.SetN<>(e1, e2, e3, e4, e5,
                                                e6);
     }
 
     /**
-     * Returns an immutable set containing seven elements.
-     * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+     * Returns an unmodifiable set containing seven elements.
+     * See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
      *
      * @param <E> the {@code Set}'s element type
      * @param e1 the first element
      * @param e2 the second element
      * @param e3 the third element

@@ -584,12 +585,12 @@
         return new ImmutableCollections.SetN<>(e1, e2, e3, e4, e5,
                                                e6, e7);
     }
 
     /**
-     * Returns an immutable set containing eight elements.
-     * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+     * Returns an unmodifiable set containing eight elements.
+     * See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
      *
      * @param <E> the {@code Set}'s element type
      * @param e1 the first element
      * @param e2 the second element
      * @param e3 the third element

@@ -608,12 +609,12 @@
         return new ImmutableCollections.SetN<>(e1, e2, e3, e4, e5,
                                                e6, e7, e8);
     }
 
     /**
-     * Returns an immutable set containing nine elements.
-     * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+     * Returns an unmodifiable set containing nine elements.
+     * See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
      *
      * @param <E> the {@code Set}'s element type
      * @param e1 the first element
      * @param e2 the second element
      * @param e3 the third element

@@ -633,12 +634,12 @@
         return new ImmutableCollections.SetN<>(e1, e2, e3, e4, e5,
                                                e6, e7, e8, e9);
     }
 
     /**
-     * Returns an immutable set containing ten elements.
-     * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+     * Returns an unmodifiable set containing ten elements.
+     * See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
      *
      * @param <E> the {@code Set}'s element type
      * @param e1 the first element
      * @param e2 the second element
      * @param e3 the third element

@@ -659,12 +660,12 @@
         return new ImmutableCollections.SetN<>(e1, e2, e3, e4, e5,
                                                e6, e7, e8, e9, e10);
     }
 
     /**
-     * Returns an immutable set containing an arbitrary number of elements.
-     * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+     * Returns an unmodifiable set containing an arbitrary number of elements.
+     * See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
      *
      * @apiNote
      * This method also accepts a single array as an argument. The element type of
      * the resulting set will be the component type of the array, and the size of
      * the set will be equal to the length of the array. To create a set with

@@ -698,6 +699,28 @@
                 return new ImmutableCollections.Set2<>(elements[0], elements[1]);
             default:
                 return new ImmutableCollections.SetN<>(elements);
         }
     }
+
+    /**
+     * Returns an unmodifiable Set containing the elements of the given Collection.
+     * Duplicate elements are permitted. If the Collection has a defined iteration order,
+     * the first element of any duplicates is preserved, and the rest are discarded.
+     * Otherwise, an arbitrary element is preserved.
+     * See <a href="#unmodifiable">Unmodifiable Sets</a> for
+     * information about the characteristics of the returned Set.
+     *
+     * @param <E> the {@code Set}'s element type
+     * @param coll the collection from which elements are drawn
+     * @return the new Set
+     * @since 10
+     */
+    @SuppressWarnings("unchecked")
+    static <E> Set<E> copyOf(Collection<? extends E> coll) {
+        if (coll instanceof ImmutableCollections.AbstractImmutableSet) {
+            return (Set<E>)coll;
+        } else {
+            return (Set<E>)Set.of(coll.stream().distinct().toArray());
+        }
+    }
 }
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