< prev index next >
src/java.base/share/classes/java/util/List.java
Print this page
rev 13824 : Remove factories from concrete collections. Increase counts to 10.
@@ -85,10 +85,23 @@
* the insertion of an ineligible element into the list 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 List Factory Methods</a></h2>
+ * <p>The {@link List#of(Object...) List.of()} factory methods
+ * provide a convenient way to create immutable lists. The {@code List}
+ * 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 disallow null elements. Attempts to create them with
+ * null elements result in {@code NullPointerException}.
+ * <li>They are serializable if all elements are serializable.
+ * </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 in this list
@@ -729,6 +742,315 @@
*/
@Override
default Spliterator<E> spliterator() {
return Spliterators.spliterator(this, Spliterator.ORDERED);
}
+
+ /**
+ * Creates an immutable list containing zero elements.
+ *
+ * See <a href="#immutable">Immutable List Factory Methods</a> for details.
+ *
+ * @param <E> the list's element type
+ * @return the newly created list
+ *
+ * @since 1.9
+ */
+ static <E> List<E> of() {
+ return Collections.emptyList();
+ }
+
+ /**
+ * Creates an immutable list containing one element.
+ *
+ * See <a href="#immutable">Immutable List Factory Methods</a> for details.
+ *
+ * @param <E> the list's element type
+ * @param e1 the single list element
+ * @return the newly created list
+ * @throws NullPointerException if the element is null
+ *
+ * @since 1.9
+ */
+ static <E> List<E> of(E e1) {
+ return Collections.singletonList(Objects.requireNonNull(e1));
+ }
+
+ /**
+ * Creates an immutable list containing two elements.
+ *
+ * See <a href="#immutable">Immutable List Factory Methods</a> for details.
+ *
+ * @param <E> the list's element type
+ * @param e1 the first list element
+ * @param e2 the second list element
+ * @return the newly created list
+ * @throws NullPointerException if an element is null
+ *
+ * @since 1.9
+ */
+ static <E> List<E> of(E e1, E e2) {
+ return Collections.unmodifiableList(
+ Arrays.asList(Objects.requireNonNull(e1),
+ Objects.requireNonNull(e2)));
+ }
+
+ /**
+ * Creates an immutable list containing three elements.
+ *
+ * See <a href="#immutable">Immutable List Factory Methods</a> for details.
+ *
+ * @param <E> the list's element type
+ * @param e1 the first list element
+ * @param e2 the second list element
+ * @param e3 the third list element
+ * @return the newly created list
+ * @throws NullPointerException if an element is null
+ *
+ * @since 1.9
+ */
+ static <E> List<E> of(E e1, E e2, E e3) {
+ return Collections.unmodifiableList(
+ Arrays.asList(Objects.requireNonNull(e1),
+ Objects.requireNonNull(e2),
+ Objects.requireNonNull(e3)));
+ }
+
+ /**
+ * Creates an immutable list containing four elements.
+ *
+ * See <a href="#immutable">Immutable List Factory Methods</a> for details.
+ *
+ * @param <E> the list's element type
+ * @param e1 the first list element
+ * @param e2 the second list element
+ * @param e3 the third list element
+ * @param e4 the fourth list element
+ * @return the newly created list
+ * @throws NullPointerException if an element is null
+ *
+ * @since 1.9
+ */
+ static <E> List<E> of(E e1, E e2, E e3, E e4) {
+ return Collections.unmodifiableList(
+ Arrays.asList(Objects.requireNonNull(e1),
+ Objects.requireNonNull(e2),
+ Objects.requireNonNull(e3),
+ Objects.requireNonNull(e4)));
+ }
+
+ /**
+ * Creates an immutable list containing five elements.
+ *
+ * See <a href="#immutable">Immutable List Factory Methods</a> for details.
+ *
+ * @param <E> the list's element type
+ * @param e1 the first list element
+ * @param e2 the second list element
+ * @param e3 the third list element
+ * @param e4 the fourth list element
+ * @param e5 the fifth list element
+ * @return the newly created list
+ * @throws NullPointerException if an element is null
+ *
+ * @since 1.9
+ */
+ static <E> List<E> of(E e1, E e2, E e3, E e4, E e5) {
+ return Collections.unmodifiableList(
+ Arrays.asList(Objects.requireNonNull(e1),
+ Objects.requireNonNull(e2),
+ Objects.requireNonNull(e3),
+ Objects.requireNonNull(e4),
+ Objects.requireNonNull(e5)));
+ }
+
+ /**
+ * Creates an immutable list containing six elements.
+ *
+ * See <a href="#immutable">Immutable List Factory Methods</a> for details.
+ *
+ * @param <E> the list's element type
+ * @param e1 the first list element
+ * @param e2 the second list element
+ * @param e3 the third list element
+ * @param e4 the fourth list element
+ * @param e5 the fifth list element
+ * @param e6 the sixth list element
+ * @return the newly created list
+ * @throws NullPointerException if an element is null
+ *
+ * @since 1.9
+ */
+ static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6) {
+ return Collections.unmodifiableList(
+ Arrays.asList(Objects.requireNonNull(e1),
+ Objects.requireNonNull(e2),
+ Objects.requireNonNull(e3),
+ Objects.requireNonNull(e4),
+ Objects.requireNonNull(e5),
+ Objects.requireNonNull(e6)));
+ }
+
+ /**
+ * Creates an immutable list containing seven elements.
+ *
+ * See <a href="#immutable">Immutable List Factory Methods</a> for details.
+ *
+ * @param <E> the list's element type
+ * @param e1 the first list element
+ * @param e2 the second list element
+ * @param e3 the third list element
+ * @param e4 the fourth list element
+ * @param e5 the fifth list element
+ * @param e6 the sixth list element
+ * @param e7 the seventh list element
+ * @return the newly created list
+ * @throws NullPointerException if an element is null
+ *
+ * @since 1.9
+ */
+ static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7) {
+ return Collections.unmodifiableList(
+ Arrays.asList(Objects.requireNonNull(e1),
+ Objects.requireNonNull(e2),
+ Objects.requireNonNull(e3),
+ Objects.requireNonNull(e4),
+ Objects.requireNonNull(e5),
+ Objects.requireNonNull(e6),
+ Objects.requireNonNull(e7)));
+ }
+
+ /**
+ * Creates an immutable list containing eight elements.
+ *
+ * See <a href="#immutable">Immutable List Factory Methods</a> for details.
+ *
+ * @param <E> the list's element type
+ * @param e1 the first list element
+ * @param e2 the second list element
+ * @param e3 the third list element
+ * @param e4 the fourth list element
+ * @param e5 the fifth list element
+ * @param e6 the sixth list element
+ * @param e7 the seventh list element
+ * @param e8 the eighth list element
+ * @return the newly created list
+ * @throws NullPointerException if an element is null
+ *
+ * @since 1.9
+ */
+ static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8) {
+ return Collections.unmodifiableList(
+ 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)));
+ }
+
+ /**
+ * Creates an immutable list containing nine elements.
+ *
+ * See <a href="#immutable">Immutable List Factory Methods</a> for details.
+ *
+ * @param <E> the list's element type
+ * @param e1 the first list element
+ * @param e2 the second list element
+ * @param e3 the third list element
+ * @param e4 the fourth list element
+ * @param e5 the fifth list element
+ * @param e6 the sixth list element
+ * @param e7 the seventh list element
+ * @param e8 the eighth list element
+ * @param e9 the ninth list element
+ * @return the newly created list
+ * @throws NullPointerException if an element is null
+ *
+ * @since 1.9
+ */
+ static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9) {
+ return Collections.unmodifiableList(
+ 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)));
+ }
+
+ /**
+ * Creates an immutable list containing ten elements.
+ *
+ * See <a href="#immutable">Immutable List Factory Methods</a> for details.
+ *
+ * @param <E> the list's element type
+ * @param e1 the first list element
+ * @param e2 the second list element
+ * @param e3 the third list element
+ * @param e4 the fourth list element
+ * @param e5 the fifth list element
+ * @param e6 the sixth list element
+ * @param e7 the seventh list element
+ * @param e8 the eighth list element
+ * @param e9 the ninth list element
+ * @param e10 the tenth list element
+ * @return the newly created list
+ * @throws NullPointerException if an element is null
+ *
+ * @since 1.9
+ */
+ static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10) {
+ return Collections.unmodifiableList(
+ 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)));
+ }
+
+ /**
+ * Creates an immutable list containing an arbitrary number of elements.
+ *
+ * See <a href="#immutable">Immutable List Factory Methods</a> for details.
+ *
+ * @apiNote
+ * This method also accepts a single array as an argument. The element type of
+ * the resulting list will be the component type of the array, and the size of
+ * the list will be equal to the length of the array. To create a list with
+ * a single element that is an array, do the following:
+ *
+ * <pre>{@code
+ * String[] array = ... ;
+ * List<String[]> list = List.<String[]>of(array);
+ * }</pre>
+ *
+ * This will cause the {@link List#of(Object) List.of(E)} method
+ * to be invoked instead.
+ *
+ * @param <E> the list's element type
+ * @param es the elements to be contained in the list
+ * @return the newly created list
+ * @throws NullPointerException if an element is null
+ *
+ * @since 1.9
+ */
+ @SafeVarargs
+ @SuppressWarnings("varargs")
+ static <E> List<E> of(E... es) {
+ for (E e : es) {
+ Objects.requireNonNull(e);
+ }
+ // NOTE: this can allow a null element to slip through
+ return Collections.unmodifiableList(Arrays.asList(es));
+ }
}
< prev index next >