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src/java.base/share/classes/java/util/Set.java
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rev 14011 : Change @since 1.9 to @since 9.
rev 14012 : Add disclaimer about mutable elements.
rev 14013 : Fix typos.
@@ -61,10 +61,27 @@
* 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 name="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}
+ * instances created by these methods have the following characteristics:
+ *
+ * <ul>
+ * <li>They cannot be modified. Attempts to modify them result in
+ * an {@code UnsupportedOperationException}.
+ * <li>They are truly immutable only if the contained elements are themselves
+ * immutable. If an element is mutated, the behavior of the set is unspecified.
+ * <li>They disallow null elements. Attempts to create them with
+ * null elements result in {@code NullPointerException}.
+ * <li>They are serializable if all elements are serializable.
+ * <li>They reject duplicate elements at creation time. Duplicate elements
+ * passed to a static factory method result in {@code IllegalArgumentException}.
+ * </ul>
+ *
* <p>This interface is a member of the
* <a href="{@docRoot}/../technotes/guides/collections/index.html">
* Java Collections Framework</a>.
*
* @param <E> the type of elements maintained by this set
@@ -408,6 +425,344 @@
*/
@Override
default Spliterator<E> spliterator() {
return Spliterators.spliterator(this, Spliterator.DISTINCT);
}
+
+ /**
+ * Creates an immutable set containing zero elements.
+ * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+ *
+ * @param <E> the set's element type
+ * @return the newly created set
+ *
+ * @since 9
+ */
+ static <E> Set<E> of() {
+ return Collections.emptySet();
+ }
+
+ /**
+ * Creates an immutable set containing one element.
+ * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+ *
+ * @param <E> the set's element type
+ * @param e1 the single set element
+ * @return the newly created set
+ * @throws NullPointerException if the element is null
+ *
+ * @since 9
+ */
+ static <E> Set<E> of(E e1) {
+ return Collections.singleton(Objects.requireNonNull(e1));
+ }
+
+ /**
+ * Creates an immutable set containing two elements.
+ * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+ *
+ * @param <E> the set's element type
+ * @param e1 the first set element
+ * @param e2 the second set element
+ * @return the newly created set
+ * @throws IllegalArgumentException if the elements are duplicates
+ * @throws NullPointerException if an element is null
+ *
+ * @since 9
+ */
+ static <E> Set<E> of(E e1, E e2) {
+ Set<E> set = new HashSet<>(Arrays.asList(Objects.requireNonNull(e1),
+ Objects.requireNonNull(e2)));
+ if (set.size() != 2) {
+ throw new IllegalArgumentException("duplicate elements");
+ }
+ return Collections.unmodifiableSet(set);
+ }
+
+ /**
+ * Creates an immutable set containing three elements.
+ * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+ *
+ * @param <E> the set's element type
+ * @param e1 the first set element
+ * @param e2 the second set element
+ * @param e3 the third set element
+ * @return the newly created set
+ * @throws IllegalArgumentException if there are any duplicate elements
+ * @throws NullPointerException if an element is null
+ *
+ * @since 9
+ */
+ static <E> Set<E> of(E e1, E e2, E e3) {
+ Set<E> set = new HashSet<>(Arrays.asList(Objects.requireNonNull(e1),
+ Objects.requireNonNull(e2),
+ Objects.requireNonNull(e3)));
+ if (set.size() != 3) {
+ throw new IllegalArgumentException("duplicate elements");
+ }
+ return Collections.unmodifiableSet(set);
+ }
+
+ /**
+ * Creates an immutable set containing four elements.
+ * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+ *
+ * @param <E> the set's element type
+ * @param e1 the first set element
+ * @param e2 the second set element
+ * @param e3 the third set element
+ * @param e4 the fourth set element
+ * @return the newly created set
+ * @throws IllegalArgumentException if there are any duplicate elements
+ * @throws NullPointerException if an element is null
+ *
+ * @since 9
+ */
+ static <E> Set<E> of(E e1, E e2, E e3, E e4) {
+ Set<E> set = new HashSet<>(Arrays.asList(Objects.requireNonNull(e1),
+ Objects.requireNonNull(e2),
+ Objects.requireNonNull(e3),
+ Objects.requireNonNull(e4)));
+ if (set.size() != 4) {
+ throw new IllegalArgumentException("duplicate elements");
+ }
+ return Collections.unmodifiableSet(set);
+ }
+
+ /**
+ * Creates an immutable set containing five elements.
+ * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+ *
+ * @param <E> the set's element type
+ * @param e1 the first set element
+ * @param e2 the second set element
+ * @param e3 the third set element
+ * @param e4 the fourth set element
+ * @param e5 the fifth set element
+ * @return the newly created set
+ * @throws IllegalArgumentException if there are any duplicate elements
+ * @throws NullPointerException if an element is null
+ *
+ * @since 9
+ */
+ static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5) {
+ Set<E> set = new HashSet<>(Arrays.asList(Objects.requireNonNull(e1),
+ Objects.requireNonNull(e2),
+ Objects.requireNonNull(e3),
+ Objects.requireNonNull(e4),
+ Objects.requireNonNull(e5)));
+ if (set.size() != 5) {
+ throw new IllegalArgumentException("duplicate elements");
+ }
+ return Collections.unmodifiableSet(set);
+ }
+
+ /**
+ * Creates an immutable set containing six elements.
+ * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+ *
+ * @param <E> the set's element type
+ * @param e1 the first set element
+ * @param e2 the second set element
+ * @param e3 the third set element
+ * @param e4 the fourth set element
+ * @param e5 the fifth set element
+ * @param e6 the sixth set element
+ * @return the newly created set
+ * @throws IllegalArgumentException if there are any duplicate elements
+ * @throws NullPointerException if an element is null
+ *
+ * @since 9
+ */
+ static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6) {
+ Set<E> set = new HashSet<>(Arrays.asList(Objects.requireNonNull(e1),
+ Objects.requireNonNull(e2),
+ Objects.requireNonNull(e3),
+ Objects.requireNonNull(e4),
+ Objects.requireNonNull(e5),
+ Objects.requireNonNull(e6)));
+ if (set.size() != 6) {
+ throw new IllegalArgumentException("duplicate elements");
+ }
+ return Collections.unmodifiableSet(set);
+ }
+
+ /**
+ * Creates an immutable set containing seven elements.
+ * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+ *
+ * @param <E> the set's element type
+ * @param e1 the first set element
+ * @param e2 the second set element
+ * @param e3 the third set element
+ * @param e4 the fourth set element
+ * @param e5 the fifth set element
+ * @param e6 the sixth set element
+ * @param e7 the seventh set element
+ * @return the newly created set
+ * @throws IllegalArgumentException if there are any duplicate elements
+ * @throws NullPointerException if an element is null
+ *
+ * @since 9
+ */
+ static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7) {
+ Set<E> set = new HashSet<>(Arrays.asList(Objects.requireNonNull(e1),
+ Objects.requireNonNull(e2),
+ Objects.requireNonNull(e3),
+ Objects.requireNonNull(e4),
+ Objects.requireNonNull(e5),
+ Objects.requireNonNull(e6),
+ Objects.requireNonNull(e7)));
+ if (set.size() != 7) {
+ throw new IllegalArgumentException("duplicate elements");
+ }
+ return Collections.unmodifiableSet(set);
+ }
+
+ /**
+ * Creates an immutable set containing eight elements.
+ * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+ *
+ * @param <E> the set's element type
+ * @param e1 the first set element
+ * @param e2 the second set element
+ * @param e3 the third set element
+ * @param e4 the fourth set element
+ * @param e5 the fifth set element
+ * @param e6 the sixth set element
+ * @param e7 the seventh set element
+ * @param e8 the eighth set element
+ * @return the newly created set
+ * @throws IllegalArgumentException if there are any duplicate elements
+ * @throws NullPointerException if an element is null
+ *
+ * @since 9
+ */
+ static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8) {
+ Set<E> set = new HashSet<>(Arrays.asList(Objects.requireNonNull(e1),
+ Objects.requireNonNull(e2),
+ Objects.requireNonNull(e3),
+ Objects.requireNonNull(e4),
+ Objects.requireNonNull(e5),
+ Objects.requireNonNull(e6),
+ Objects.requireNonNull(e7),
+ Objects.requireNonNull(e8)));
+ if (set.size() != 8) {
+ throw new IllegalArgumentException("duplicate elements");
+ }
+ return Collections.unmodifiableSet(set);
+ }
+
+ /**
+ * Creates an immutable set containing nine elements.
+ * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+ *
+ * @param <E> the set's element type
+ * @param e1 the first set element
+ * @param e2 the second set element
+ * @param e3 the third set element
+ * @param e4 the fourth set element
+ * @param e5 the fifth set element
+ * @param e6 the sixth set element
+ * @param e7 the seventh set element
+ * @param e8 the eighth set element
+ * @param e9 the ninth set element
+ * @return the newly created set
+ * @throws IllegalArgumentException if there are any duplicate elements
+ * @throws NullPointerException if an element is null
+ *
+ * @since 9
+ */
+ static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9) {
+ Set<E> set = new HashSet<>(Arrays.asList(Objects.requireNonNull(e1),
+ Objects.requireNonNull(e2),
+ Objects.requireNonNull(e3),
+ Objects.requireNonNull(e4),
+ Objects.requireNonNull(e5),
+ Objects.requireNonNull(e6),
+ Objects.requireNonNull(e7),
+ Objects.requireNonNull(e8),
+ Objects.requireNonNull(e9)));
+ if (set.size() != 9) {
+ throw new IllegalArgumentException("duplicate elements");
+ }
+ return Collections.unmodifiableSet(set);
+ }
+
+ /**
+ * Creates an immutable set containing ten elements.
+ * See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
+ *
+ * @param <E> the set's element type
+ * @param e1 the first set element
+ * @param e2 the second set element
+ * @param e3 the third set element
+ * @param e4 the fourth set element
+ * @param e5 the fifth set element
+ * @param e6 the sixth set element
+ * @param e7 the seventh set element
+ * @param e8 the eighth set element
+ * @param e9 the ninth set element
+ * @param e10 the tenth set element
+ * @return the newly created set
+ * @throws IllegalArgumentException if there are any duplicate elements
+ * @throws NullPointerException if an element is null
+ *
+ * @since 9
+ */
+ static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10) {
+ Set<E> set = new HashSet<>(Arrays.asList(Objects.requireNonNull(e1),
+ Objects.requireNonNull(e2),
+ Objects.requireNonNull(e3),
+ Objects.requireNonNull(e4),
+ Objects.requireNonNull(e5),
+ Objects.requireNonNull(e6),
+ Objects.requireNonNull(e7),
+ Objects.requireNonNull(e8),
+ Objects.requireNonNull(e9),
+ Objects.requireNonNull(e10)));
+ if (set.size() != 10) {
+ throw new IllegalArgumentException("duplicate elements");
+ }
+ return Collections.unmodifiableSet(set);
+ }
+
+ /**
+ * Creates an immutable set containing an arbitrary number of elements.
+ * See <a href="#immutable">Immutable Set Static Factory Methods</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
+ * a single element that is an array, do the following:
+ *
+ * <pre>{@code
+ * String[] array = ... ;
+ * Set<String[]> list = Set.<String[]>of(array);
+ * }</pre>
+ *
+ * This will cause the {@link Set#of(Object) Set.of(E)} method
+ * to be invoked instead.
+ *
+ * @param <E> the set's element type
+ * @param es the elements to be contained in the set
+ * @return the newly created set
+ * @throws IllegalArgumentException if there are any duplicate elements
+ * @throws NullPointerException if an element is null or if the array is null
+ *
+ * @since 9
+ */
+ @SafeVarargs
+ @SuppressWarnings("varargs")
+ static <E> Set<E> of(E... es) {
+ for (E e : es) { // throws NPE if es is null
+ Objects.requireNonNull(e);
+ }
+ // NOTE: this can allow a null element to slip through
+ Set<E> set = new HashSet<>(Arrays.asList(es));
+ if (set.size() != es.length) {
+ throw new IllegalArgumentException("duplicate elements");
+ }
+ return Collections.unmodifiableSet(set);
+ }
}
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