--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/java.base/share/classes/java/util/Map.java Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,1658 @@
+/*
+ * Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.util;
+
+import java.util.function.BiConsumer;
+import java.util.function.BiFunction;
+import java.util.function.Function;
+import java.io.Serializable;
+
+/**
+ * An object that maps keys to values. A map cannot contain duplicate keys;
+ * each key can map to at most one value.
+ *
+ * <p>This interface takes the place of the {@code Dictionary} class, which
+ * was a totally abstract class rather than an interface.
+ *
+ * <p>The {@code Map} interface provides three <i>collection views</i>, which
+ * allow a map's contents to be viewed as a set of keys, collection of values,
+ * or set of key-value mappings. The <i>order</i> of a map is defined as
+ * the order in which the iterators on the map's collection views return their
+ * elements. Some map implementations, like the {@code TreeMap} class, make
+ * specific guarantees as to their order; others, like the {@code HashMap}
+ * class, do not.
+ *
+ * <p>Note: great care must be exercised if mutable objects are used as map
+ * keys. The behavior of a map is not specified if the value of an object is
+ * changed in a manner that affects {@code equals} comparisons while the
+ * object is a key in the map. A special case of this prohibition is that it
+ * is not permissible for a map to contain itself as a key. While it is
+ * permissible for a map to contain itself as a value, extreme caution is
+ * advised: the {@code equals} and {@code hashCode} methods are no longer
+ * well defined on such a map.
+ *
+ * <p>All general-purpose map implementation classes should provide two
+ * "standard" constructors: a void (no arguments) constructor which creates an
+ * empty map, and a constructor with a single argument of type {@code Map},
+ * which creates a new map with the same key-value mappings as its argument.
+ * In effect, the latter constructor allows the user to copy any map,
+ * producing an equivalent map of the desired class. There is no way to
+ * enforce this recommendation (as interfaces cannot contain constructors) but
+ * all of the general-purpose map implementations in the JDK comply.
+ *
+ * <p>The "destructive" methods contained in this interface, that is, the
+ * methods that modify the map on which they operate, are specified to throw
+ * {@code UnsupportedOperationException} if this map does not support the
+ * operation. If this is the case, these methods may, but are not required
+ * to, throw an {@code UnsupportedOperationException} if the invocation would
+ * have no effect on the map. For example, invoking the {@link #putAll(Map)}
+ * method on an unmodifiable map may, but is not required to, throw the
+ * exception if the map whose mappings are to be "superimposed" is empty.
+ *
+ * <p>Some map implementations have restrictions on the keys and values they
+ * may contain. For example, some implementations prohibit null keys and
+ * values, and some have restrictions on the types of their keys. Attempting
+ * to insert an ineligible key or value throws an unchecked exception,
+ * typically {@code NullPointerException} or {@code ClassCastException}.
+ * Attempting to query the presence of an ineligible key or value may throw an
+ * exception, or it may simply return false; some implementations will exhibit
+ * the former behavior and some will exhibit the latter. More generally,
+ * attempting an operation on an ineligible key or value whose completion
+ * would not result in the insertion of an ineligible element into the map 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.
+ *
+ * <p>Many methods in Collections Framework interfaces are defined
+ * in terms of the {@link Object#equals(Object) equals} method. For
+ * example, the specification for the {@link #containsKey(Object)
+ * containsKey(Object key)} method says: "returns {@code true} if and
+ * only if this map contains a mapping for a key {@code k} such that
+ * {@code (key==null ? k==null : key.equals(k))}." This specification should
+ * <i>not</i> be construed to imply that invoking {@code Map.containsKey}
+ * with a non-null argument {@code key} will cause {@code key.equals(k)} to
+ * be invoked for any key {@code k}. Implementations are free to
+ * implement optimizations whereby the {@code equals} invocation is avoided,
+ * for example, by first comparing the hash codes of the two keys. (The
+ * {@link Object#hashCode()} specification guarantees that two objects with
+ * unequal hash codes cannot be equal.) More generally, implementations of
+ * the various Collections Framework interfaces are free to take advantage of
+ * the specified behavior of underlying {@link Object} methods wherever the
+ * implementor deems it appropriate.
+ *
+ * <p>Some map operations which perform recursive traversal of the map may fail
+ * with an exception for self-referential instances where the map directly or
+ * 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 id="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 are <em>structurally immutable</em>. Keys and values cannot be added,
+ * removed, or updated. Calling any mutator method will always cause
+ * {@code UnsupportedOperationException} to be thrown.
+ * However, if the contained keys or values are themselves mutable, this may cause the
+ * Map to behave inconsistently or its contents to appear to change.
+ * <li>They disallow {@code null} keys and values. Attempts to create them with
+ * {@code 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}.
+ * <li>The iteration order of mappings is unspecified and is subject to change.
+ * <li>They are <a href="../lang/doc-files/ValueBased.html">value-based</a>.
+ * Callers should make no assumptions about the identity of the returned instances.
+ * Factories are free to create new instances or reuse existing ones. Therefore,
+ * identity-sensitive operations on these instances (reference equality ({@code ==}),
+ * identity hash code, and synchronization) are unreliable and should be avoided.
+ * <li>They are serialized as specified on the
+ * <a href="{@docRoot}/serialized-form.html#java.util.CollSer">Serialized Form</a>
+ * page.
+ * </ul>
+ *
+ * <p>This interface is a member of the
+ * <a href="{@docRoot}/java/util/package-summary.html#CollectionsFramework">
+ * Java Collections Framework</a>.
+ *
+ * @param <K> the type of keys maintained by this map
+ * @param <V> the type of mapped values
+ *
+ * @author Josh Bloch
+ * @see HashMap
+ * @see TreeMap
+ * @see Hashtable
+ * @see SortedMap
+ * @see Collection
+ * @see Set
+ * @since 1.2
+ */
+public interface Map<K, V> {
+ // Query Operations
+
+ /**
+ * Returns the number of key-value mappings in this map. If the
+ * map contains more than {@code Integer.MAX_VALUE} elements, returns
+ * {@code Integer.MAX_VALUE}.
+ *
+ * @return the number of key-value mappings in this map
+ */
+ int size();
+
+ /**
+ * Returns {@code true} if this map contains no key-value mappings.
+ *
+ * @return {@code true} if this map contains no key-value mappings
+ */
+ boolean isEmpty();
+
+ /**
+ * Returns {@code true} if this map contains a mapping for the specified
+ * key. More formally, returns {@code true} if and only if
+ * this map contains a mapping for a key {@code k} such that
+ * {@code Objects.equals(key, k)}. (There can be
+ * at most one such mapping.)
+ *
+ * @param key key whose presence in this map is to be tested
+ * @return {@code true} if this map contains a mapping for the specified
+ * key
+ * @throws ClassCastException if the key is of an inappropriate type for
+ * this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws NullPointerException if the specified key is null and this map
+ * does not permit null keys
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ */
+ boolean containsKey(Object key);
+
+ /**
+ * Returns {@code true} if this map maps one or more keys to the
+ * specified value. More formally, returns {@code true} if and only if
+ * this map contains at least one mapping to a value {@code v} such that
+ * {@code Objects.equals(value, v)}. This operation
+ * will probably require time linear in the map size for most
+ * implementations of the {@code Map} interface.
+ *
+ * @param value value whose presence in this map is to be tested
+ * @return {@code true} if this map maps one or more keys to the
+ * specified value
+ * @throws ClassCastException if the value is of an inappropriate type for
+ * this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws NullPointerException if the specified value is null and this
+ * map does not permit null values
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ */
+ boolean containsValue(Object value);
+
+ /**
+ * Returns the value to which the specified key is mapped,
+ * or {@code null} if this map contains no mapping for the key.
+ *
+ * <p>More formally, if this map contains a mapping from a key
+ * {@code k} to a value {@code v} such that
+ * {@code Objects.equals(key, k)},
+ * then this method returns {@code v}; otherwise
+ * it returns {@code null}. (There can be at most one such mapping.)
+ *
+ * <p>If this map permits null values, then a return value of
+ * {@code null} does not <i>necessarily</i> indicate that the map
+ * contains no mapping for the key; it's also possible that the map
+ * explicitly maps the key to {@code null}. The {@link #containsKey
+ * containsKey} operation may be used to distinguish these two cases.
+ *
+ * @param key the key whose associated value is to be returned
+ * @return the value to which the specified key is mapped, or
+ * {@code null} if this map contains no mapping for the key
+ * @throws ClassCastException if the key is of an inappropriate type for
+ * this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws NullPointerException if the specified key is null and this map
+ * does not permit null keys
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ */
+ V get(Object key);
+
+ // Modification Operations
+
+ /**
+ * Associates the specified value with the specified key in this map
+ * (optional operation). If the map previously contained a mapping for
+ * the key, the old value is replaced by the specified value. (A map
+ * {@code m} is said to contain a mapping for a key {@code k} if and only
+ * if {@link #containsKey(Object) m.containsKey(k)} would return
+ * {@code true}.)
+ *
+ * @param key key with which the specified value is to be associated
+ * @param value value to be associated with the specified key
+ * @return the previous value associated with {@code key}, or
+ * {@code null} if there was no mapping for {@code key}.
+ * (A {@code null} return can also indicate that the map
+ * previously associated {@code null} with {@code key},
+ * if the implementation supports {@code null} values.)
+ * @throws UnsupportedOperationException if the {@code put} operation
+ * is not supported by this map
+ * @throws ClassCastException if the class of the specified key or value
+ * prevents it from being stored in this map
+ * @throws NullPointerException if the specified key or value is null
+ * and this map does not permit null keys or values
+ * @throws IllegalArgumentException if some property of the specified key
+ * or value prevents it from being stored in this map
+ */
+ V put(K key, V value);
+
+ /**
+ * Removes the mapping for a key from this map if it is present
+ * (optional operation). More formally, if this map contains a mapping
+ * from key {@code k} to value {@code v} such that
+ * {@code Objects.equals(key, k)}, that mapping
+ * is removed. (The map can contain at most one such mapping.)
+ *
+ * <p>Returns the value to which this map previously associated the key,
+ * or {@code null} if the map contained no mapping for the key.
+ *
+ * <p>If this map permits null values, then a return value of
+ * {@code null} does not <i>necessarily</i> indicate that the map
+ * contained no mapping for the key; it's also possible that the map
+ * explicitly mapped the key to {@code null}.
+ *
+ * <p>The map will not contain a mapping for the specified key once the
+ * call returns.
+ *
+ * @param key key whose mapping is to be removed from the map
+ * @return the previous value associated with {@code key}, or
+ * {@code null} if there was no mapping for {@code key}.
+ * @throws UnsupportedOperationException if the {@code remove} operation
+ * is not supported by this map
+ * @throws ClassCastException if the key is of an inappropriate type for
+ * this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws NullPointerException if the specified key is null and this
+ * map does not permit null keys
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ */
+ V remove(Object key);
+
+
+ // Bulk Operations
+
+ /**
+ * Copies all of the mappings from the specified map to this map
+ * (optional operation). The effect of this call is equivalent to that
+ * of calling {@link #put(Object,Object) put(k, v)} on this map once
+ * for each mapping from key {@code k} to value {@code v} in the
+ * specified map. The behavior of this operation is undefined if the
+ * specified map is modified while the operation is in progress.
+ *
+ * @param m mappings to be stored in this map
+ * @throws UnsupportedOperationException if the {@code putAll} operation
+ * is not supported by this map
+ * @throws ClassCastException if the class of a key or value in the
+ * specified map prevents it from being stored in this map
+ * @throws NullPointerException if the specified map is null, or if
+ * this map does not permit null keys or values, and the
+ * specified map contains null keys or values
+ * @throws IllegalArgumentException if some property of a key or value in
+ * the specified map prevents it from being stored in this map
+ */
+ void putAll(Map<? extends K, ? extends V> m);
+
+ /**
+ * Removes all of the mappings from this map (optional operation).
+ * The map will be empty after this call returns.
+ *
+ * @throws UnsupportedOperationException if the {@code clear} operation
+ * is not supported by this map
+ */
+ void clear();
+
+
+ // Views
+
+ /**
+ * Returns a {@link Set} view of the keys contained in this map.
+ * The set is backed by the map, so changes to the map are
+ * reflected in the set, and vice-versa. If the map is modified
+ * while an iteration over the set is in progress (except through
+ * the iterator's own {@code remove} operation), the results of
+ * the iteration are undefined. The set supports element removal,
+ * which removes the corresponding mapping from the map, via the
+ * {@code Iterator.remove}, {@code Set.remove},
+ * {@code removeAll}, {@code retainAll}, and {@code clear}
+ * operations. It does not support the {@code add} or {@code addAll}
+ * operations.
+ *
+ * @return a set view of the keys contained in this map
+ */
+ Set<K> keySet();
+
+ /**
+ * Returns a {@link Collection} view of the values contained in this map.
+ * The collection is backed by the map, so changes to the map are
+ * reflected in the collection, and vice-versa. If the map is
+ * modified while an iteration over the collection is in progress
+ * (except through the iterator's own {@code remove} operation),
+ * the results of the iteration are undefined. The collection
+ * supports element removal, which removes the corresponding
+ * mapping from the map, via the {@code Iterator.remove},
+ * {@code Collection.remove}, {@code removeAll},
+ * {@code retainAll} and {@code clear} operations. It does not
+ * support the {@code add} or {@code addAll} operations.
+ *
+ * @return a collection view of the values contained in this map
+ */
+ Collection<V> values();
+
+ /**
+ * Returns a {@link Set} view of the mappings contained in this map.
+ * The set is backed by the map, so changes to the map are
+ * reflected in the set, and vice-versa. If the map is modified
+ * while an iteration over the set is in progress (except through
+ * the iterator's own {@code remove} operation, or through the
+ * {@code setValue} operation on a map entry returned by the
+ * iterator) the results of the iteration are undefined. The set
+ * supports element removal, which removes the corresponding
+ * mapping from the map, via the {@code Iterator.remove},
+ * {@code Set.remove}, {@code removeAll}, {@code retainAll} and
+ * {@code clear} operations. It does not support the
+ * {@code add} or {@code addAll} operations.
+ *
+ * @return a set view of the mappings contained in this map
+ */
+ Set<Map.Entry<K, V>> entrySet();
+
+ /**
+ * A map entry (key-value pair). The {@code Map.entrySet} method returns
+ * a collection-view of the map, whose elements are of this class. The
+ * <i>only</i> way to obtain a reference to a map entry is from the
+ * iterator of this collection-view. These {@code Map.Entry} objects are
+ * valid <i>only</i> for the duration of the iteration; more formally,
+ * the behavior of a map entry is undefined if the backing map has been
+ * modified after the entry was returned by the iterator, except through
+ * the {@code setValue} operation on the map entry.
+ *
+ * @see Map#entrySet()
+ * @since 1.2
+ */
+ interface Entry<K, V> {
+ /**
+ * Returns the key corresponding to this entry.
+ *
+ * @return the key corresponding to this entry
+ * @throws IllegalStateException implementations may, but are not
+ * required to, throw this exception if the entry has been
+ * removed from the backing map.
+ */
+ K getKey();
+
+ /**
+ * Returns the value corresponding to this entry. If the mapping
+ * has been removed from the backing map (by the iterator's
+ * {@code remove} operation), the results of this call are undefined.
+ *
+ * @return the value corresponding to this entry
+ * @throws IllegalStateException implementations may, but are not
+ * required to, throw this exception if the entry has been
+ * removed from the backing map.
+ */
+ V getValue();
+
+ /**
+ * Replaces the value corresponding to this entry with the specified
+ * value (optional operation). (Writes through to the map.) The
+ * behavior of this call is undefined if the mapping has already been
+ * removed from the map (by the iterator's {@code remove} operation).
+ *
+ * @param value new value to be stored in this entry
+ * @return old value corresponding to the entry
+ * @throws UnsupportedOperationException if the {@code put} operation
+ * is not supported by the backing map
+ * @throws ClassCastException if the class of the specified value
+ * prevents it from being stored in the backing map
+ * @throws NullPointerException if the backing map does not permit
+ * null values, and the specified value is null
+ * @throws IllegalArgumentException if some property of this value
+ * prevents it from being stored in the backing map
+ * @throws IllegalStateException implementations may, but are not
+ * required to, throw this exception if the entry has been
+ * removed from the backing map.
+ */
+ V setValue(V value);
+
+ /**
+ * Compares the specified object with this entry for equality.
+ * Returns {@code true} if the given object is also a map entry and
+ * the two entries represent the same mapping. More formally, two
+ * entries {@code e1} and {@code e2} represent the same mapping
+ * if<pre>
+ * (e1.getKey()==null ?
+ * e2.getKey()==null : e1.getKey().equals(e2.getKey())) &&
+ * (e1.getValue()==null ?
+ * e2.getValue()==null : e1.getValue().equals(e2.getValue()))
+ * </pre>
+ * This ensures that the {@code equals} method works properly across
+ * different implementations of the {@code Map.Entry} interface.
+ *
+ * @param o object to be compared for equality with this map entry
+ * @return {@code true} if the specified object is equal to this map
+ * entry
+ */
+ boolean equals(Object o);
+
+ /**
+ * Returns the hash code value for this map entry. The hash code
+ * of a map entry {@code e} is defined to be: <pre>
+ * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^
+ * (e.getValue()==null ? 0 : e.getValue().hashCode())
+ * </pre>
+ * This ensures that {@code e1.equals(e2)} implies that
+ * {@code e1.hashCode()==e2.hashCode()} for any two Entries
+ * {@code e1} and {@code e2}, as required by the general
+ * contract of {@code Object.hashCode}.
+ *
+ * @return the hash code value for this map entry
+ * @see Object#hashCode()
+ * @see Object#equals(Object)
+ * @see #equals(Object)
+ */
+ int hashCode();
+
+ /**
+ * Returns a comparator that compares {@link Map.Entry} in natural order on key.
+ *
+ * <p>The returned comparator is serializable and throws {@link
+ * NullPointerException} when comparing an entry with a null key.
+ *
+ * @param <K> the {@link Comparable} type of then map keys
+ * @param <V> the type of the map values
+ * @return a comparator that compares {@link Map.Entry} in natural order on key.
+ * @see Comparable
+ * @since 1.8
+ */
+ public static <K extends Comparable<? super K>, V> Comparator<Map.Entry<K, V>> comparingByKey() {
+ return (Comparator<Map.Entry<K, V>> & Serializable)
+ (c1, c2) -> c1.getKey().compareTo(c2.getKey());
+ }
+
+ /**
+ * Returns a comparator that compares {@link Map.Entry} in natural order on value.
+ *
+ * <p>The returned comparator is serializable and throws {@link
+ * NullPointerException} when comparing an entry with null values.
+ *
+ * @param <K> the type of the map keys
+ * @param <V> the {@link Comparable} type of the map values
+ * @return a comparator that compares {@link Map.Entry} in natural order on value.
+ * @see Comparable
+ * @since 1.8
+ */
+ public static <K, V extends Comparable<? super V>> Comparator<Map.Entry<K, V>> comparingByValue() {
+ return (Comparator<Map.Entry<K, V>> & Serializable)
+ (c1, c2) -> c1.getValue().compareTo(c2.getValue());
+ }
+
+ /**
+ * Returns a comparator that compares {@link Map.Entry} by key using the given
+ * {@link Comparator}.
+ *
+ * <p>The returned comparator is serializable if the specified comparator
+ * is also serializable.
+ *
+ * @param <K> the type of the map keys
+ * @param <V> the type of the map values
+ * @param cmp the key {@link Comparator}
+ * @return a comparator that compares {@link Map.Entry} by the key.
+ * @since 1.8
+ */
+ public static <K, V> Comparator<Map.Entry<K, V>> comparingByKey(Comparator<? super K> cmp) {
+ Objects.requireNonNull(cmp);
+ return (Comparator<Map.Entry<K, V>> & Serializable)
+ (c1, c2) -> cmp.compare(c1.getKey(), c2.getKey());
+ }
+
+ /**
+ * Returns a comparator that compares {@link Map.Entry} by value using the given
+ * {@link Comparator}.
+ *
+ * <p>The returned comparator is serializable if the specified comparator
+ * is also serializable.
+ *
+ * @param <K> the type of the map keys
+ * @param <V> the type of the map values
+ * @param cmp the value {@link Comparator}
+ * @return a comparator that compares {@link Map.Entry} by the value.
+ * @since 1.8
+ */
+ public static <K, V> Comparator<Map.Entry<K, V>> comparingByValue(Comparator<? super V> cmp) {
+ Objects.requireNonNull(cmp);
+ return (Comparator<Map.Entry<K, V>> & Serializable)
+ (c1, c2) -> cmp.compare(c1.getValue(), c2.getValue());
+ }
+ }
+
+ // Comparison and hashing
+
+ /**
+ * Compares the specified object with this map for equality. Returns
+ * {@code true} if the given object is also a map and the two maps
+ * represent the same mappings. More formally, two maps {@code m1} and
+ * {@code m2} represent the same mappings if
+ * {@code m1.entrySet().equals(m2.entrySet())}. This ensures that the
+ * {@code equals} method works properly across different implementations
+ * of the {@code Map} interface.
+ *
+ * @param o object to be compared for equality with this map
+ * @return {@code true} if the specified object is equal to this map
+ */
+ boolean equals(Object o);
+
+ /**
+ * Returns the hash code value for this map. The hash code of a map is
+ * defined to be the sum of the hash codes of each entry in the map's
+ * {@code entrySet()} view. This ensures that {@code m1.equals(m2)}
+ * implies that {@code m1.hashCode()==m2.hashCode()} for any two maps
+ * {@code m1} and {@code m2}, as required by the general contract of
+ * {@link Object#hashCode}.
+ *
+ * @return the hash code value for this map
+ * @see Map.Entry#hashCode()
+ * @see Object#equals(Object)
+ * @see #equals(Object)
+ */
+ int hashCode();
+
+ // Defaultable methods
+
+ /**
+ * Returns the value to which the specified key is mapped, or
+ * {@code defaultValue} if this map contains no mapping for the key.
+ *
+ * @implSpec
+ * The default implementation makes no guarantees about synchronization
+ * or atomicity properties of this method. Any implementation providing
+ * atomicity guarantees must override this method and document its
+ * concurrency properties.
+ *
+ * @param key the key whose associated value is to be returned
+ * @param defaultValue the default mapping of the key
+ * @return the value to which the specified key is mapped, or
+ * {@code defaultValue} if this map contains no mapping for the key
+ * @throws ClassCastException if the key is of an inappropriate type for
+ * this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws NullPointerException if the specified key is null and this map
+ * does not permit null keys
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @since 1.8
+ */
+ default V getOrDefault(Object key, V defaultValue) {
+ V v;
+ return (((v = get(key)) != null) || containsKey(key))
+ ? v
+ : defaultValue;
+ }
+
+ /**
+ * Performs the given action for each entry in this map until all entries
+ * have been processed or the action throws an exception. Unless
+ * otherwise specified by the implementing class, actions are performed in
+ * the order of entry set iteration (if an iteration order is specified.)
+ * Exceptions thrown by the action are relayed to the caller.
+ *
+ * @implSpec
+ * The default implementation is equivalent to, for this {@code map}:
+ * <pre> {@code
+ * for (Map.Entry<K, V> entry : map.entrySet())
+ * action.accept(entry.getKey(), entry.getValue());
+ * }</pre>
+ *
+ * The default implementation makes no guarantees about synchronization
+ * or atomicity properties of this method. Any implementation providing
+ * atomicity guarantees must override this method and document its
+ * concurrency properties.
+ *
+ * @param action The action to be performed for each entry
+ * @throws NullPointerException if the specified action is null
+ * @throws ConcurrentModificationException if an entry is found to be
+ * removed during iteration
+ * @since 1.8
+ */
+ default void forEach(BiConsumer<? super K, ? super V> action) {
+ Objects.requireNonNull(action);
+ for (Map.Entry<K, V> entry : entrySet()) {
+ K k;
+ V v;
+ try {
+ k = entry.getKey();
+ v = entry.getValue();
+ } catch (IllegalStateException ise) {
+ // this usually means the entry is no longer in the map.
+ throw new ConcurrentModificationException(ise);
+ }
+ action.accept(k, v);
+ }
+ }
+
+ /**
+ * Replaces each entry's value with the result of invoking the given
+ * function on that entry until all entries have been processed or the
+ * function throws an exception. Exceptions thrown by the function are
+ * relayed to the caller.
+ *
+ * @implSpec
+ * <p>The default implementation is equivalent to, for this {@code map}:
+ * <pre> {@code
+ * for (Map.Entry<K, V> entry : map.entrySet())
+ * entry.setValue(function.apply(entry.getKey(), entry.getValue()));
+ * }</pre>
+ *
+ * <p>The default implementation makes no guarantees about synchronization
+ * or atomicity properties of this method. Any implementation providing
+ * atomicity guarantees must override this method and document its
+ * concurrency properties.
+ *
+ * @param function the function to apply to each entry
+ * @throws UnsupportedOperationException if the {@code set} operation
+ * is not supported by this map's entry set iterator.
+ * @throws ClassCastException if the class of a replacement value
+ * prevents it from being stored in this map
+ * @throws NullPointerException if the specified function is null, or the
+ * specified replacement value is null, and this map does not permit null
+ * values
+ * @throws ClassCastException if a replacement value is of an inappropriate
+ * type for this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws NullPointerException if function or a replacement value is null,
+ * and this map does not permit null keys or values
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws IllegalArgumentException if some property of a replacement value
+ * prevents it from being stored in this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws ConcurrentModificationException if an entry is found to be
+ * removed during iteration
+ * @since 1.8
+ */
+ default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
+ Objects.requireNonNull(function);
+ for (Map.Entry<K, V> entry : entrySet()) {
+ K k;
+ V v;
+ try {
+ k = entry.getKey();
+ v = entry.getValue();
+ } catch (IllegalStateException ise) {
+ // this usually means the entry is no longer in the map.
+ throw new ConcurrentModificationException(ise);
+ }
+
+ // ise thrown from function is not a cme.
+ v = function.apply(k, v);
+
+ try {
+ entry.setValue(v);
+ } catch (IllegalStateException ise) {
+ // this usually means the entry is no longer in the map.
+ throw new ConcurrentModificationException(ise);
+ }
+ }
+ }
+
+ /**
+ * If the specified key is not already associated with a value (or is mapped
+ * to {@code null}) associates it with the given value and returns
+ * {@code null}, else returns the current value.
+ *
+ * @implSpec
+ * The default implementation is equivalent to, for this {@code
+ * map}:
+ *
+ * <pre> {@code
+ * V v = map.get(key);
+ * if (v == null)
+ * v = map.put(key, value);
+ *
+ * return v;
+ * }</pre>
+ *
+ * <p>The default implementation makes no guarantees about synchronization
+ * or atomicity properties of this method. Any implementation providing
+ * atomicity guarantees must override this method and document its
+ * concurrency properties.
+ *
+ * @param key key with which the specified value is to be associated
+ * @param value value to be associated with the specified key
+ * @return the previous value associated with the specified key, or
+ * {@code null} if there was no mapping for the key.
+ * (A {@code null} return can also indicate that the map
+ * previously associated {@code null} with the key,
+ * if the implementation supports null values.)
+ * @throws UnsupportedOperationException if the {@code put} operation
+ * is not supported by this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws ClassCastException if the key or value is of an inappropriate
+ * type for this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws NullPointerException if the specified key or value is null,
+ * and this map does not permit null keys or values
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws IllegalArgumentException if some property of the specified key
+ * or value prevents it from being stored in this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @since 1.8
+ */
+ default V putIfAbsent(K key, V value) {
+ V v = get(key);
+ if (v == null) {
+ v = put(key, value);
+ }
+
+ return v;
+ }
+
+ /**
+ * Removes the entry for the specified key only if it is currently
+ * mapped to the specified value.
+ *
+ * @implSpec
+ * The default implementation is equivalent to, for this {@code map}:
+ *
+ * <pre> {@code
+ * if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
+ * map.remove(key);
+ * return true;
+ * } else
+ * return false;
+ * }</pre>
+ *
+ * <p>The default implementation makes no guarantees about synchronization
+ * or atomicity properties of this method. Any implementation providing
+ * atomicity guarantees must override this method and document its
+ * concurrency properties.
+ *
+ * @param key key with which the specified value is associated
+ * @param value value expected to be associated with the specified key
+ * @return {@code true} if the value was removed
+ * @throws UnsupportedOperationException if the {@code remove} operation
+ * is not supported by this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws ClassCastException if the key or value is of an inappropriate
+ * type for this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws NullPointerException if the specified key or value is null,
+ * and this map does not permit null keys or values
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @since 1.8
+ */
+ default boolean remove(Object key, Object value) {
+ Object curValue = get(key);
+ if (!Objects.equals(curValue, value) ||
+ (curValue == null && !containsKey(key))) {
+ return false;
+ }
+ remove(key);
+ return true;
+ }
+
+ /**
+ * Replaces the entry for the specified key only if currently
+ * mapped to the specified value.
+ *
+ * @implSpec
+ * The default implementation is equivalent to, for this {@code map}:
+ *
+ * <pre> {@code
+ * if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
+ * map.put(key, newValue);
+ * return true;
+ * } else
+ * return false;
+ * }</pre>
+ *
+ * The default implementation does not throw NullPointerException
+ * for maps that do not support null values if oldValue is null unless
+ * newValue is also null.
+ *
+ * <p>The default implementation makes no guarantees about synchronization
+ * or atomicity properties of this method. Any implementation providing
+ * atomicity guarantees must override this method and document its
+ * concurrency properties.
+ *
+ * @param key key with which the specified value is associated
+ * @param oldValue value expected to be associated with the specified key
+ * @param newValue value to be associated with the specified key
+ * @return {@code true} if the value was replaced
+ * @throws UnsupportedOperationException if the {@code put} operation
+ * is not supported by this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws ClassCastException if the class of a specified key or value
+ * prevents it from being stored in this map
+ * @throws NullPointerException if a specified key or newValue is null,
+ * and this map does not permit null keys or values
+ * @throws NullPointerException if oldValue is null and this map does not
+ * permit null values
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws IllegalArgumentException if some property of a specified key
+ * or value prevents it from being stored in this map
+ * @since 1.8
+ */
+ default boolean replace(K key, V oldValue, V newValue) {
+ Object curValue = get(key);
+ if (!Objects.equals(curValue, oldValue) ||
+ (curValue == null && !containsKey(key))) {
+ return false;
+ }
+ put(key, newValue);
+ return true;
+ }
+
+ /**
+ * Replaces the entry for the specified key only if it is
+ * currently mapped to some value.
+ *
+ * @implSpec
+ * The default implementation is equivalent to, for this {@code map}:
+ *
+ * <pre> {@code
+ * if (map.containsKey(key)) {
+ * return map.put(key, value);
+ * } else
+ * return null;
+ * }</pre>
+ *
+ * <p>The default implementation makes no guarantees about synchronization
+ * or atomicity properties of this method. Any implementation providing
+ * atomicity guarantees must override this method and document its
+ * concurrency properties.
+ *
+ * @param key key with which the specified value is associated
+ * @param value value to be associated with the specified key
+ * @return the previous value associated with the specified key, or
+ * {@code null} if there was no mapping for the key.
+ * (A {@code null} return can also indicate that the map
+ * previously associated {@code null} with the key,
+ * if the implementation supports null values.)
+ * @throws UnsupportedOperationException if the {@code put} operation
+ * is not supported by this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws ClassCastException if the class of the specified key or value
+ * prevents it from being stored in this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws NullPointerException if the specified key or value is null,
+ * and this map does not permit null keys or values
+ * @throws IllegalArgumentException if some property of the specified key
+ * or value prevents it from being stored in this map
+ * @since 1.8
+ */
+ default V replace(K key, V value) {
+ V curValue;
+ if (((curValue = get(key)) != null) || containsKey(key)) {
+ curValue = put(key, value);
+ }
+ return curValue;
+ }
+
+ /**
+ * If the specified key is not already associated with a value (or is mapped
+ * to {@code null}), attempts to compute its value using the given mapping
+ * function and enters it into this map unless {@code null}.
+ *
+ * <p>If the mapping function returns {@code null}, no mapping is recorded.
+ * If the mapping function itself throws an (unchecked) exception, the
+ * exception is rethrown, and no mapping is recorded. The most
+ * common usage is to construct a new object serving as an initial
+ * mapped value or memoized result, as in:
+ *
+ * <pre> {@code
+ * map.computeIfAbsent(key, k -> new Value(f(k)));
+ * }</pre>
+ *
+ * <p>Or to implement a multi-value map, {@code Map<K,Collection<V>>},
+ * supporting multiple values per key:
+ *
+ * <pre> {@code
+ * map.computeIfAbsent(key, k -> new HashSet<V>()).add(v);
+ * }</pre>
+ *
+ * <p>The mapping function should not modify this map during computation.
+ *
+ * @implSpec
+ * The default implementation is equivalent to the following steps for this
+ * {@code map}, then returning the current value or {@code null} if now
+ * absent:
+ *
+ * <pre> {@code
+ * if (map.get(key) == null) {
+ * V newValue = mappingFunction.apply(key);
+ * if (newValue != null)
+ * map.put(key, newValue);
+ * }
+ * }</pre>
+ *
+ * <p>The default implementation makes no guarantees about detecting if the
+ * mapping function modifies this map during computation and, if
+ * appropriate, reporting an error. Non-concurrent implementations should
+ * override this method and, on a best-effort basis, throw a
+ * {@code ConcurrentModificationException} if it is detected that the
+ * mapping function modifies this map during computation. Concurrent
+ * implementations should override this method and, on a best-effort basis,
+ * throw an {@code IllegalStateException} if it is detected that the
+ * mapping function modifies this map during computation and as a result
+ * computation would never complete.
+ *
+ * <p>The default implementation makes no guarantees about synchronization
+ * or atomicity properties of this method. Any implementation providing
+ * atomicity guarantees must override this method and document its
+ * concurrency properties. In particular, all implementations of
+ * subinterface {@link java.util.concurrent.ConcurrentMap} must document
+ * whether the mapping function is applied once atomically only if the value
+ * is not present.
+ *
+ * @param key key with which the specified value is to be associated
+ * @param mappingFunction the mapping function to compute a value
+ * @return the current (existing or computed) value associated with
+ * the specified key, or null if the computed value is null
+ * @throws NullPointerException if the specified key is null and
+ * this map does not support null keys, or the mappingFunction
+ * is null
+ * @throws UnsupportedOperationException if the {@code put} operation
+ * is not supported by this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws ClassCastException if the class of the specified key or value
+ * prevents it from being stored in this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws IllegalArgumentException if some property of the specified key
+ * or value prevents it from being stored in this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @since 1.8
+ */
+ default V computeIfAbsent(K key,
+ Function<? super K, ? extends V> mappingFunction) {
+ Objects.requireNonNull(mappingFunction);
+ V v;
+ if ((v = get(key)) == null) {
+ V newValue;
+ if ((newValue = mappingFunction.apply(key)) != null) {
+ put(key, newValue);
+ return newValue;
+ }
+ }
+
+ return v;
+ }
+
+ /**
+ * If the value for the specified key is present and non-null, attempts to
+ * compute a new mapping given the key and its current mapped value.
+ *
+ * <p>If the remapping function returns {@code null}, the mapping is removed.
+ * If the remapping function itself throws an (unchecked) exception, the
+ * exception is rethrown, and the current mapping is left unchanged.
+ *
+ * <p>The remapping function should not modify this map during computation.
+ *
+ * @implSpec
+ * The default implementation is equivalent to performing the following
+ * steps for this {@code map}, then returning the current value or
+ * {@code null} if now absent:
+ *
+ * <pre> {@code
+ * if (map.get(key) != null) {
+ * V oldValue = map.get(key);
+ * V newValue = remappingFunction.apply(key, oldValue);
+ * if (newValue != null)
+ * map.put(key, newValue);
+ * else
+ * map.remove(key);
+ * }
+ * }</pre>
+ *
+ * <p>The default implementation makes no guarantees about detecting if the
+ * remapping function modifies this map during computation and, if
+ * appropriate, reporting an error. Non-concurrent implementations should
+ * override this method and, on a best-effort basis, throw a
+ * {@code ConcurrentModificationException} if it is detected that the
+ * remapping function modifies this map during computation. Concurrent
+ * implementations should override this method and, on a best-effort basis,
+ * throw an {@code IllegalStateException} if it is detected that the
+ * remapping function modifies this map during computation and as a result
+ * computation would never complete.
+ *
+ * <p>The default implementation makes no guarantees about synchronization
+ * or atomicity properties of this method. Any implementation providing
+ * atomicity guarantees must override this method and document its
+ * concurrency properties. In particular, all implementations of
+ * subinterface {@link java.util.concurrent.ConcurrentMap} must document
+ * whether the remapping function is applied once atomically only if the
+ * value is not present.
+ *
+ * @param key key with which the specified value is to be associated
+ * @param remappingFunction the remapping function to compute a value
+ * @return the new value associated with the specified key, or null if none
+ * @throws NullPointerException if the specified key is null and
+ * this map does not support null keys, or the
+ * remappingFunction is null
+ * @throws UnsupportedOperationException if the {@code put} operation
+ * is not supported by this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws ClassCastException if the class of the specified key or value
+ * prevents it from being stored in this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws IllegalArgumentException if some property of the specified key
+ * or value prevents it from being stored in this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @since 1.8
+ */
+ default V computeIfPresent(K key,
+ BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
+ Objects.requireNonNull(remappingFunction);
+ V oldValue;
+ if ((oldValue = get(key)) != null) {
+ V newValue = remappingFunction.apply(key, oldValue);
+ if (newValue != null) {
+ put(key, newValue);
+ return newValue;
+ } else {
+ remove(key);
+ return null;
+ }
+ } else {
+ return null;
+ }
+ }
+
+ /**
+ * Attempts to compute a mapping for the specified key and its current
+ * mapped value (or {@code null} if there is no current mapping). For
+ * example, to either create or append a {@code String} msg to a value
+ * mapping:
+ *
+ * <pre> {@code
+ * map.compute(key, (k, v) -> (v == null) ? msg : v.concat(msg))}</pre>
+ * (Method {@link #merge merge()} is often simpler to use for such purposes.)
+ *
+ * <p>If the remapping function returns {@code null}, the mapping is removed
+ * (or remains absent if initially absent). If the remapping function
+ * itself throws an (unchecked) exception, the exception is rethrown, and
+ * the current mapping is left unchanged.
+ *
+ * <p>The remapping function should not modify this map during computation.
+ *
+ * @implSpec
+ * The default implementation is equivalent to performing the following
+ * steps for this {@code map}, then returning the current value or
+ * {@code null} if absent:
+ *
+ * <pre> {@code
+ * V oldValue = map.get(key);
+ * V newValue = remappingFunction.apply(key, oldValue);
+ * if (oldValue != null) {
+ * if (newValue != null)
+ * map.put(key, newValue);
+ * else
+ * map.remove(key);
+ * } else {
+ * if (newValue != null)
+ * map.put(key, newValue);
+ * else
+ * return null;
+ * }
+ * }</pre>
+ *
+ * <p>The default implementation makes no guarantees about detecting if the
+ * remapping function modifies this map during computation and, if
+ * appropriate, reporting an error. Non-concurrent implementations should
+ * override this method and, on a best-effort basis, throw a
+ * {@code ConcurrentModificationException} if it is detected that the
+ * remapping function modifies this map during computation. Concurrent
+ * implementations should override this method and, on a best-effort basis,
+ * throw an {@code IllegalStateException} if it is detected that the
+ * remapping function modifies this map during computation and as a result
+ * computation would never complete.
+ *
+ * <p>The default implementation makes no guarantees about synchronization
+ * or atomicity properties of this method. Any implementation providing
+ * atomicity guarantees must override this method and document its
+ * concurrency properties. In particular, all implementations of
+ * subinterface {@link java.util.concurrent.ConcurrentMap} must document
+ * whether the remapping function is applied once atomically only if the
+ * value is not present.
+ *
+ * @param key key with which the specified value is to be associated
+ * @param remappingFunction the remapping function to compute a value
+ * @return the new value associated with the specified key, or null if none
+ * @throws NullPointerException if the specified key is null and
+ * this map does not support null keys, or the
+ * remappingFunction is null
+ * @throws UnsupportedOperationException if the {@code put} operation
+ * is not supported by this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws ClassCastException if the class of the specified key or value
+ * prevents it from being stored in this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws IllegalArgumentException if some property of the specified key
+ * or value prevents it from being stored in this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @since 1.8
+ */
+ default V compute(K key,
+ BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
+ Objects.requireNonNull(remappingFunction);
+ V oldValue = get(key);
+
+ V newValue = remappingFunction.apply(key, oldValue);
+ if (newValue == null) {
+ // delete mapping
+ if (oldValue != null || containsKey(key)) {
+ // something to remove
+ remove(key);
+ return null;
+ } else {
+ // nothing to do. Leave things as they were.
+ return null;
+ }
+ } else {
+ // add or replace old mapping
+ put(key, newValue);
+ return newValue;
+ }
+ }
+
+ /**
+ * If the specified key is not already associated with a value or is
+ * associated with null, associates it with the given non-null value.
+ * Otherwise, replaces the associated value with the results of the given
+ * remapping function, or removes if the result is {@code null}. This
+ * method may be of use when combining multiple mapped values for a key.
+ * For example, to either create or append a {@code String msg} to a
+ * value mapping:
+ *
+ * <pre> {@code
+ * map.merge(key, msg, String::concat)
+ * }</pre>
+ *
+ * <p>If the remapping function returns {@code null}, the mapping is removed.
+ * If the remapping function itself throws an (unchecked) exception, the
+ * exception is rethrown, and the current mapping is left unchanged.
+ *
+ * <p>The remapping function should not modify this map during computation.
+ *
+ * @implSpec
+ * The default implementation is equivalent to performing the following
+ * steps for this {@code map}, then returning the current value or
+ * {@code null} if absent:
+ *
+ * <pre> {@code
+ * V oldValue = map.get(key);
+ * V newValue = (oldValue == null) ? value :
+ * remappingFunction.apply(oldValue, value);
+ * if (newValue == null)
+ * map.remove(key);
+ * else
+ * map.put(key, newValue);
+ * }</pre>
+ *
+ * <p>The default implementation makes no guarantees about detecting if the
+ * remapping function modifies this map during computation and, if
+ * appropriate, reporting an error. Non-concurrent implementations should
+ * override this method and, on a best-effort basis, throw a
+ * {@code ConcurrentModificationException} if it is detected that the
+ * remapping function modifies this map during computation. Concurrent
+ * implementations should override this method and, on a best-effort basis,
+ * throw an {@code IllegalStateException} if it is detected that the
+ * remapping function modifies this map during computation and as a result
+ * computation would never complete.
+ *
+ * <p>The default implementation makes no guarantees about synchronization
+ * or atomicity properties of this method. Any implementation providing
+ * atomicity guarantees must override this method and document its
+ * concurrency properties. In particular, all implementations of
+ * subinterface {@link java.util.concurrent.ConcurrentMap} must document
+ * whether the remapping function is applied once atomically only if the
+ * value is not present.
+ *
+ * @param key key with which the resulting value is to be associated
+ * @param value the non-null value to be merged with the existing value
+ * associated with the key or, if no existing value or a null value
+ * is associated with the key, to be associated with the key
+ * @param remappingFunction the remapping function to recompute a value if
+ * present
+ * @return the new value associated with the specified key, or null if no
+ * value is associated with the key
+ * @throws UnsupportedOperationException if the {@code put} operation
+ * is not supported by this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws ClassCastException if the class of the specified key or value
+ * prevents it from being stored in this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws IllegalArgumentException if some property of the specified key
+ * or value prevents it from being stored in this map
+ * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
+ * @throws NullPointerException if the specified key is null and this map
+ * does not support null keys or the value or remappingFunction is
+ * null
+ * @since 1.8
+ */
+ default V merge(K key, V value,
+ BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
+ Objects.requireNonNull(remappingFunction);
+ Objects.requireNonNull(value);
+ V oldValue = get(key);
+ V newValue = (oldValue == null) ? value :
+ remappingFunction.apply(oldValue, value);
+ if (newValue == null) {
+ remove(key);
+ } else {
+ put(key, newValue);
+ }
+ return newValue;
+ }
+
+ /**
+ * Returns an immutable map containing zero mappings.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the {@code Map}'s key type
+ * @param <V> the {@code Map}'s value type
+ * @return an empty {@code Map}
+ *
+ * @since 9
+ */
+ static <K, V> Map<K, V> of() {
+ return ImmutableCollections.Map0.instance();
+ }
+
+ /**
+ * Returns an immutable map containing a single mapping.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the {@code Map}'s key type
+ * @param <V> the {@code Map}'s value type
+ * @param k1 the mapping's key
+ * @param v1 the mapping's value
+ * @return a {@code Map} containing the specified mapping
+ * @throws NullPointerException if the key or the value is {@code null}
+ *
+ * @since 9
+ */
+ static <K, V> Map<K, V> of(K k1, V v1) {
+ return new ImmutableCollections.Map1<>(k1, v1);
+ }
+
+ /**
+ * Returns an immutable map containing two mappings.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the {@code Map}'s key type
+ * @param <V> the {@code 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 a {@code Map} containing the specified mappings
+ * @throws IllegalArgumentException if the keys are duplicates
+ * @throws NullPointerException if any key or value is {@code null}
+ *
+ * @since 9
+ */
+ static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2) {
+ return new ImmutableCollections.MapN<>(k1, v1, k2, v2);
+ }
+
+ /**
+ * Returns an immutable map containing three mappings.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the {@code Map}'s key type
+ * @param <V> the {@code 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 a {@code Map} containing the specified mappings
+ * @throws IllegalArgumentException if there are any duplicate keys
+ * @throws NullPointerException if any key or value is {@code null}
+ *
+ * @since 9
+ */
+ static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3) {
+ return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3);
+ }
+
+ /**
+ * Returns an immutable map containing four mappings.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the {@code Map}'s key type
+ * @param <V> the {@code 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 a {@code Map} containing the specified mappings
+ * @throws IllegalArgumentException if there are any duplicate keys
+ * @throws NullPointerException if any key or value is {@code 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) {
+ return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4);
+ }
+
+ /**
+ * Returns an immutable map containing five mappings.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the {@code Map}'s key type
+ * @param <V> the {@code 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 a {@code Map} containing the specified mappings
+ * @throws IllegalArgumentException if there are any duplicate keys
+ * @throws NullPointerException if any key or value is {@code 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) {
+ return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5);
+ }
+
+ /**
+ * Returns an immutable map containing six mappings.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the {@code Map}'s key type
+ * @param <V> the {@code 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 a {@code Map} containing the specified mappings
+ * @throws IllegalArgumentException if there are any duplicate keys
+ * @throws NullPointerException if any key or value is {@code 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) {
+ return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5,
+ k6, v6);
+ }
+
+ /**
+ * Returns an immutable map containing seven mappings.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the {@code Map}'s key type
+ * @param <V> the {@code 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 a {@code Map} containing the specified mappings
+ * @throws IllegalArgumentException if there are any duplicate keys
+ * @throws NullPointerException if any key or value is {@code 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) {
+ return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5,
+ k6, v6, k7, v7);
+ }
+
+ /**
+ * Returns an immutable map containing eight mappings.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the {@code Map}'s key type
+ * @param <V> the {@code 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 a {@code Map} containing the specified mappings
+ * @throws IllegalArgumentException if there are any duplicate keys
+ * @throws NullPointerException if any key or value is {@code 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) {
+ return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5,
+ k6, v6, k7, v7, k8, v8);
+ }
+
+ /**
+ * Returns an immutable map containing nine mappings.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the {@code Map}'s key type
+ * @param <V> the {@code 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 a {@code Map} containing the specified mappings
+ * @throws IllegalArgumentException if there are any duplicate keys
+ * @throws NullPointerException if any key or value is {@code 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) {
+ return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5,
+ k6, v6, k7, v7, k8, v8, k9, v9);
+ }
+
+ /**
+ * Returns an immutable map containing ten mappings.
+ * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
+ *
+ * @param <K> the {@code Map}'s key type
+ * @param <V> the {@code 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 a {@code Map} containing the specified mappings
+ * @throws IllegalArgumentException if there are any duplicate keys
+ * @throws NullPointerException if any key or value is {@code 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) {
+ return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5,
+ k6, v6, k7, v7, k8, v8, k9, v9, k10, v10);
+ }
+
+ /**
+ * Returns an immutable map containing keys and values extracted from the given entries.
+ * The entries themselves are not stored in the map.
+ * 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 {@code Map}'s key type
+ * @param <V> the {@code Map}'s value type
+ * @param entries {@code Map.Entry}s containing the keys and values from which the map is populated
+ * @return a {@code Map} containing the specified mappings
+ * @throws IllegalArgumentException if there are any duplicate keys
+ * @throws NullPointerException if any entry, key, or value is {@code null}, or if
+ * the {@code entries} array is {@code null}
+ *
+ * @see Map#entry Map.entry()
+ * @since 9
+ */
+ @SafeVarargs
+ @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();
+ } else if (entries.length == 1) {
+ return new ImmutableCollections.Map1<>(entries[0].getKey(),
+ entries[0].getValue());
+ } else {
+ Object[] kva = new Object[entries.length << 1];
+ int a = 0;
+ for (Entry<? extends K, ? extends V> entry : entries) {
+ kva[a++] = entry.getKey();
+ kva[a++] = entry.getValue();
+ }
+ return new ImmutableCollections.MapN<>(kva);
+ }
+ }
+
+ /**
+ * Returns 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 {@code Entry} instances created by this method have the following characteristics:
+ *
+ * <ul>
+ * <li>They disallow {@code null} keys and values. Attempts to create them using a {@code null}
+ * key or value result in {@code NullPointerException}.
+ * <li>They are immutable. Calls to {@link Entry#setValue Entry.setValue()}
+ * on a returned {@code Entry} result in {@code UnsupportedOperationException}.
+ * <li>They are not serializable.
+ * <li>They are <a href="../lang/doc-files/ValueBased.html">value-based</a>.
+ * Callers should make no assumptions about the identity of the returned instances.
+ * This method is free to create new instances or reuse existing ones. Therefore,
+ * identity-sensitive operations on these instances (reference equality ({@code ==}),
+ * identity hash code, and synchronization) are unreliable and should be avoided.
+ * </ul>
+ *
+ * @apiNote
+ * For a serializable {@code Entry}, see {@link AbstractMap.SimpleEntry} or
+ * {@link AbstractMap.SimpleImmutableEntry}.
+ *
+ * @param <K> the key's type
+ * @param <V> the value's type
+ * @param k the key
+ * @param v the value
+ * @return an {@code Entry} containing the specified key and value
+ * @throws NullPointerException if the key or value is {@code 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);
+ }
+}