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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 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 are <em>structurally immutable</em>. Keys and values cannot be added,

 * removed, or updated. Attempts to do so result in {@code UnsupportedOperationException}.

 * 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.

 * </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

 * @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