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src/java.base/share/classes/java/util/Map.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.
@@ -108,10 +108,29 @@
* indirectly contains itself. This includes the {@code clone()},
* {@code equals()}, {@code hashCode()} and {@code toString()} methods.
* Implementations may optionally handle the self-referential scenario, however
* most current implementations do not do so.
*
+ * <h2><a name="immutable">Immutable Map Static Factory Methods</a></h2>
+ * <p>The {@link Map#of() Map.of()} and
+ * {@link Map#ofEntries(Map.Entry...) Map.ofEntries()}
+ * static factory methods provide a convenient way to create immutable maps.
+ * The {@code Map}
+ * 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 keys and values are themselves
+ * immutable. If a key or value is mutated, the behavior of the map is unspecified.
+ * <li>They disallow null keys and values. Attempts to create them with
+ * null keys or values result in {@code NullPointerException}.
+ * <li>They are serializable if all keys and values are serializable.
+ * <li>They reject duplicate keys at creation time. Duplicate keys
+ * 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 <K> the type of keys maintained by this map
@@ -1231,6 +1250,456 @@
} else {
put(key, newValue);
}
return newValue;
}
+
+ /**
+ * Creates an immutable map containing zero mappings.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the map's key type
+ * @param <V> the map's value type
+ * @return the newly created map
+ *
+ * @since 9
+ */
+ static <K,V> Map<K,V> of() {
+ return Collections.emptyMap();
+ }
+
+ /**
+ * Creates an immutable map containing a single mapping.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the map's key type
+ * @param <V> the map's value type
+ * @param k1 the mapping's key
+ * @param v1 the mapping's value
+ * @return the newly created map
+ * @throws NullPointerException if the key or the value is null
+ *
+ * @since 9
+ */
+ static <K,V> Map<K,V> of(K k1, V v1) {
+ return Collections.singletonMap(Objects.requireNonNull(k1), Objects.requireNonNull(v1));
+ }
+
+ /**
+ * Creates an immutable map containing two mappings.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the map's key type
+ * @param <V> the map's value type
+ * @param k1 the first mapping's key
+ * @param v1 the first mapping's value
+ * @param k2 the second mapping's key
+ * @param v2 the second mapping's value
+ * @return the newly created map
+ * @throws IllegalArgumentException if the keys are duplicates
+ * @throws NullPointerException if any key or value is null
+ *
+ * @since 9
+ */
+ static <K,V> Map<K,V> of(K k1, V v1, K k2, V v2) {
+ Map<K,V> map = new HashMap<>(3);
+ map.put(Objects.requireNonNull(k1), Objects.requireNonNull(v1));
+ map.put(Objects.requireNonNull(k2), Objects.requireNonNull(v2));
+ if (map.size() != 2) {
+ throw new IllegalArgumentException("duplicate keys");
+ }
+ return Collections.unmodifiableMap(map);
+ }
+
+ /**
+ * Creates an immutable map containing three mappings.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the map's key type
+ * @param <V> the map's value type
+ * @param k1 the first mapping's key
+ * @param v1 the first mapping's value
+ * @param k2 the second mapping's key
+ * @param v2 the second mapping's value
+ * @param k3 the third mapping's key
+ * @param v3 the third mapping's value
+ * @return the newly created map
+ * @throws IllegalArgumentException if any keys are duplicates
+ * @throws NullPointerException if any key or value is null
+ *
+ * @since 9
+ */
+ static <K,V> Map<K,V> of(K k1, V v1, K k2, V v2, K k3, V v3) {
+ Map<K,V> map = new HashMap<>(5);
+ map.put(Objects.requireNonNull(k1), Objects.requireNonNull(v1));
+ map.put(Objects.requireNonNull(k2), Objects.requireNonNull(v2));
+ map.put(Objects.requireNonNull(k3), Objects.requireNonNull(v3));
+ if (map.size() != 3) {
+ throw new IllegalArgumentException("duplicate keys");
+ }
+ return Collections.unmodifiableMap(map);
+ }
+
+ /**
+ * Creates an immutable map containing four mappings.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the map's key type
+ * @param <V> the map's value type
+ * @param k1 the first mapping's key
+ * @param v1 the first mapping's value
+ * @param k2 the second mapping's key
+ * @param v2 the second mapping's value
+ * @param k3 the third mapping's key
+ * @param v3 the third mapping's value
+ * @param k4 the fourth mapping's key
+ * @param v4 the fourth mapping's value
+ * @return the newly created map
+ * @throws IllegalArgumentException if any keys are duplicates
+ * @throws NullPointerException if any key or value is null
+ *
+ * @since 9
+ */
+ static <K,V> Map<K,V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4) {
+ Map<K,V> map = new HashMap<>(6);
+ map.put(Objects.requireNonNull(k1), Objects.requireNonNull(v1));
+ map.put(Objects.requireNonNull(k2), Objects.requireNonNull(v2));
+ map.put(Objects.requireNonNull(k3), Objects.requireNonNull(v3));
+ map.put(Objects.requireNonNull(k4), Objects.requireNonNull(v4));
+ if (map.size() != 4) {
+ throw new IllegalArgumentException("duplicate keys");
+ }
+ return Collections.unmodifiableMap(map);
+ }
+
+ /**
+ * Creates an immutable map containing five mappings.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the map's key type
+ * @param <V> the map's value type
+ * @param k1 the first mapping's key
+ * @param v1 the first mapping's value
+ * @param k2 the second mapping's key
+ * @param v2 the second mapping's value
+ * @param k3 the third mapping's key
+ * @param v3 the third mapping's value
+ * @param k4 the fourth mapping's key
+ * @param v4 the fourth mapping's value
+ * @param k5 the fifth mapping's key
+ * @param v5 the fifth mapping's value
+ * @return the newly created map
+ * @throws IllegalArgumentException if any keys are duplicates
+ * @throws NullPointerException if any key or value is null
+ *
+ * @since 9
+ */
+ static <K,V> Map<K,V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5) {
+ Map<K,V> map = new HashMap<>(7);
+ map.put(Objects.requireNonNull(k1), Objects.requireNonNull(v1));
+ map.put(Objects.requireNonNull(k2), Objects.requireNonNull(v2));
+ map.put(Objects.requireNonNull(k3), Objects.requireNonNull(v3));
+ map.put(Objects.requireNonNull(k4), Objects.requireNonNull(v4));
+ map.put(Objects.requireNonNull(k5), Objects.requireNonNull(v5));
+ if (map.size() != 5) {
+ throw new IllegalArgumentException("duplicate keys");
+ }
+ return Collections.unmodifiableMap(map);
+ }
+
+ /**
+ * Creates an immutable map containing six mappings.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the map's key type
+ * @param <V> the map's value type
+ * @param k1 the first mapping's key
+ * @param v1 the first mapping's value
+ * @param k2 the second mapping's key
+ * @param v2 the second mapping's value
+ * @param k3 the third mapping's key
+ * @param v3 the third mapping's value
+ * @param k4 the fourth mapping's key
+ * @param v4 the fourth mapping's value
+ * @param k5 the fifth mapping's key
+ * @param v5 the fifth mapping's value
+ * @param k6 the sixth mapping's key
+ * @param v6 the sixth mapping's value
+ * @return the newly created map
+ * @throws IllegalArgumentException if any keys are duplicates
+ * @throws NullPointerException if any key or value is null
+ *
+ * @since 9
+ */
+ static <K,V> Map<K,V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5,
+ K k6, V v6) {
+ Map<K,V> map = new HashMap<>(9);
+ map.put(Objects.requireNonNull(k1), Objects.requireNonNull(v1));
+ map.put(Objects.requireNonNull(k2), Objects.requireNonNull(v2));
+ map.put(Objects.requireNonNull(k3), Objects.requireNonNull(v3));
+ map.put(Objects.requireNonNull(k4), Objects.requireNonNull(v4));
+ map.put(Objects.requireNonNull(k5), Objects.requireNonNull(v5));
+ map.put(Objects.requireNonNull(k6), Objects.requireNonNull(v6));
+ if (map.size() != 6) {
+ throw new IllegalArgumentException("duplicate keys");
+ }
+ return Collections.unmodifiableMap(map);
+ }
+
+ /**
+ * Creates an immutable map containing seven mappings.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the map's key type
+ * @param <V> the map's value type
+ * @param k1 the first mapping's key
+ * @param v1 the first mapping's value
+ * @param k2 the second mapping's key
+ * @param v2 the second mapping's value
+ * @param k3 the third mapping's key
+ * @param v3 the third mapping's value
+ * @param k4 the fourth mapping's key
+ * @param v4 the fourth mapping's value
+ * @param k5 the fifth mapping's key
+ * @param v5 the fifth mapping's value
+ * @param k6 the sixth mapping's key
+ * @param v6 the sixth mapping's value
+ * @param k7 the seventh mapping's key
+ * @param v7 the seventh mapping's value
+ * @return the newly created map
+ * @throws IllegalArgumentException if any keys are duplicates
+ * @throws NullPointerException if any key or value is null
+ *
+ * @since 9
+ */
+ static <K,V> Map<K,V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5,
+ K k6, V v6, K k7, V v7) {
+ Map<K,V> map = new HashMap<>(10);
+ map.put(Objects.requireNonNull(k1), Objects.requireNonNull(v1));
+ map.put(Objects.requireNonNull(k2), Objects.requireNonNull(v2));
+ map.put(Objects.requireNonNull(k3), Objects.requireNonNull(v3));
+ map.put(Objects.requireNonNull(k4), Objects.requireNonNull(v4));
+ map.put(Objects.requireNonNull(k5), Objects.requireNonNull(v5));
+ map.put(Objects.requireNonNull(k6), Objects.requireNonNull(v6));
+ map.put(Objects.requireNonNull(k7), Objects.requireNonNull(v7));
+ if (map.size() != 7) {
+ throw new IllegalArgumentException("duplicate keys");
+ }
+ return Collections.unmodifiableMap(map);
+ }
+
+ /**
+ * Creates an immutable map containing eight mappings.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the map's key type
+ * @param <V> the map's value type
+ * @param k1 the first mapping's key
+ * @param v1 the first mapping's value
+ * @param k2 the second mapping's key
+ * @param v2 the second mapping's value
+ * @param k3 the third mapping's key
+ * @param v3 the third mapping's value
+ * @param k4 the fourth mapping's key
+ * @param v4 the fourth mapping's value
+ * @param k5 the fifth mapping's key
+ * @param v5 the fifth mapping's value
+ * @param k6 the sixth mapping's key
+ * @param v6 the sixth mapping's value
+ * @param k7 the seventh mapping's key
+ * @param v7 the seventh mapping's value
+ * @param k8 the eighth mapping's key
+ * @param v8 the eighth mapping's value
+ * @return the newly created map
+ * @throws IllegalArgumentException if any keys are duplicates
+ * @throws NullPointerException if any key or value is null
+ *
+ * @since 9
+ */
+ static <K,V> Map<K,V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5,
+ K k6, V v6, K k7, V v7, K k8, V v8) {
+ Map<K,V> map = new HashMap<>(11);
+ map.put(Objects.requireNonNull(k1), Objects.requireNonNull(v1));
+ map.put(Objects.requireNonNull(k2), Objects.requireNonNull(v2));
+ map.put(Objects.requireNonNull(k3), Objects.requireNonNull(v3));
+ map.put(Objects.requireNonNull(k4), Objects.requireNonNull(v4));
+ map.put(Objects.requireNonNull(k5), Objects.requireNonNull(v5));
+ map.put(Objects.requireNonNull(k6), Objects.requireNonNull(v6));
+ map.put(Objects.requireNonNull(k7), Objects.requireNonNull(v7));
+ map.put(Objects.requireNonNull(k8), Objects.requireNonNull(v8));
+ if (map.size() != 8) {
+ throw new IllegalArgumentException("duplicate keys");
+ }
+ return Collections.unmodifiableMap(map);
+ }
+
+ /**
+ * Creates an immutable map containing nine mappings.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the map's key type
+ * @param <V> the map's value type
+ * @param k1 the first mapping's key
+ * @param v1 the first mapping's value
+ * @param k2 the second mapping's key
+ * @param v2 the second mapping's value
+ * @param k3 the third mapping's key
+ * @param v3 the third mapping's value
+ * @param k4 the fourth mapping's key
+ * @param v4 the fourth mapping's value
+ * @param k5 the fifth mapping's key
+ * @param v5 the fifth mapping's value
+ * @param k6 the sixth mapping's key
+ * @param v6 the sixth mapping's value
+ * @param k7 the seventh mapping's key
+ * @param v7 the seventh mapping's value
+ * @param k8 the eighth mapping's key
+ * @param v8 the eighth mapping's value
+ * @param k9 the ninth mapping's key
+ * @param v9 the ninth mapping's value
+ * @return the newly created map
+ * @throws IllegalArgumentException if any keys are duplicates
+ * @throws NullPointerException if any key or value is null
+ *
+ * @since 9
+ */
+ static <K,V> Map<K,V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5,
+ K k6, V v6, K k7, V v7, K k8, V v8, K k9, V v9) {
+ Map<K,V> map = new HashMap<>(13);
+ map.put(Objects.requireNonNull(k1), Objects.requireNonNull(v1));
+ map.put(Objects.requireNonNull(k2), Objects.requireNonNull(v2));
+ map.put(Objects.requireNonNull(k3), Objects.requireNonNull(v3));
+ map.put(Objects.requireNonNull(k4), Objects.requireNonNull(v4));
+ map.put(Objects.requireNonNull(k5), Objects.requireNonNull(v5));
+ map.put(Objects.requireNonNull(k6), Objects.requireNonNull(v6));
+ map.put(Objects.requireNonNull(k7), Objects.requireNonNull(v7));
+ map.put(Objects.requireNonNull(k8), Objects.requireNonNull(v8));
+ map.put(Objects.requireNonNull(k9), Objects.requireNonNull(v9));
+ if (map.size() != 9) {
+ throw new IllegalArgumentException("duplicate keys");
+ }
+ return Collections.unmodifiableMap(map);
+ }
+
+ /**
+ * Creates an immutable map containing ten mappings.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the map's key type
+ * @param <V> the map's value type
+ * @param k1 the first mapping's key
+ * @param v1 the first mapping's value
+ * @param k2 the second mapping's key
+ * @param v2 the second mapping's value
+ * @param k3 the third mapping's key
+ * @param v3 the third mapping's value
+ * @param k4 the fourth mapping's key
+ * @param v4 the fourth mapping's value
+ * @param k5 the fifth mapping's key
+ * @param v5 the fifth mapping's value
+ * @param k6 the sixth mapping's key
+ * @param v6 the sixth mapping's value
+ * @param k7 the seventh mapping's key
+ * @param v7 the seventh mapping's value
+ * @param k8 the eighth mapping's key
+ * @param v8 the eighth mapping's value
+ * @param k9 the ninth mapping's key
+ * @param v9 the ninth mapping's value
+ * @param k10 the tenth mapping's key
+ * @param v10 the tenth mapping's value
+ * @return the newly created map
+ * @throws IllegalArgumentException if any keys are duplicates
+ * @throws NullPointerException if any key or value is null
+ *
+ * @since 9
+ */
+ static <K,V> Map<K,V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5,
+ K k6, V v6, K k7, V v7, K k8, V v8, K k9, V v9, K k10, V v10) {
+ Map<K,V> map = new HashMap<>(14);
+ map.put(Objects.requireNonNull(k1), Objects.requireNonNull(v1));
+ map.put(Objects.requireNonNull(k2), Objects.requireNonNull(v2));
+ map.put(Objects.requireNonNull(k3), Objects.requireNonNull(v3));
+ map.put(Objects.requireNonNull(k4), Objects.requireNonNull(v4));
+ map.put(Objects.requireNonNull(k5), Objects.requireNonNull(v5));
+ map.put(Objects.requireNonNull(k6), Objects.requireNonNull(v6));
+ map.put(Objects.requireNonNull(k7), Objects.requireNonNull(v7));
+ map.put(Objects.requireNonNull(k8), Objects.requireNonNull(v8));
+ map.put(Objects.requireNonNull(k9), Objects.requireNonNull(v9));
+ map.put(Objects.requireNonNull(k10), Objects.requireNonNull(v10));
+ if (map.size() != 10) {
+ throw new IllegalArgumentException("duplicate keys");
+ }
+ return Collections.unmodifiableMap(map);
+ }
+
+ /**
+ * Creates an immutable map containing keys and values from the given entries.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @apiNote
+ * It is convenient to create the map entries using the {@link Map#entry Map.entry()} method.
+ * For example,
+ *
+ * <pre>{@code
+ * import static java.util.Map.entry;
+ *
+ * Map<Integer,String> map = Map.ofEntries(
+ * entry(1, "a"),
+ * entry(2, "b"),
+ * entry(3, "c"),
+ * ...
+ * entry(26, "z"));
+ * }</pre>
+ *
+ * @param <K> the map's key type
+ * @param <V> the map's value type
+ * @param entries the keys and values with which the map is populated
+ * @return the newly created {@code Map}
+ * @throws IllegalArgumentException if any keys are duplicates
+ * @throws NullPointerException if any entry, key, or value is null, or if
+ * the {@code entries} array is null
+ *
+ * @see Map#entry Map.entry()
+ * @since 9
+ */
+ @SafeVarargs
+ @SuppressWarnings("varargs")
+ static <K,V> Map<K,V> ofEntries(Entry<K,V>... entries) {
+ Map<K,V> map = new HashMap<>(entries.length * 4 / 3 + 1); // throws NPE if entries is null
+ for (Entry<K,V> e : entries) {
+ Objects.requireNonNull(e);
+ map.put(Objects.requireNonNull(e.getKey()), Objects.requireNonNull(e.getValue()));
+ }
+ if (map.size() != entries.length) {
+ throw new IllegalArgumentException("duplicate elements");
+ }
+ return Collections.unmodifiableMap(map);
+ }
+
+ /**
+ * Creates an immutable {@link Entry} containing the given key and value.
+ * These entries are suitable for populating {@code Map} instances using the
+ * {@link Map#ofEntries Map.ofEntries()} method.
+ * The key and the value must not be null. Calling {@link Entry#setValue Entry.setValue()}
+ * on the returned {@code Entry} results in an {@code UnsupportedOperationException}
+ * being thrown. The returned {@code Entry} is not guaranteed to be serializable.
+ *
+ * <p>The returned {@code Entry} is a <a href="../lang/doc-files/ValueBased.html">value-based</a>
+ * class; use of identity-sensitive operations (including reference equality
+ * ({@code ==}), identity hash code, or synchronization) on any returned values
+ * may have unpredictable results and should be avoided.
+ *
+ * @param <K> the key's type
+ * @param <V> the value's type
+ * @param k the key
+ * @param v the value
+ * @return the new {@code Entry}
+ * @throws NullPointerException if the key or value is null
+ *
+ * @see Map#ofEntries Map.ofEntries()
+ * @since 9
+ */
+ static <K,V> Entry<K,V> entry(K k, V v) {
+ // KeyValueHolder checks for nulls
+ return new KeyValueHolder<>(k, v);
+ }
}
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