/*
 * Copyright (c) 1997, 2023, 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 Torello.Java.ReadOnly;

import java.util.*;

import java.util.function.BiConsumer;
import java.io.Serializable;

/**
 * Immutable variant of Java Collections Framework interface
 * <CODE>java&#46;util&#46;Map&lt;K, V&gt;</CODE>.
 * 
 * <EMBED CLASS='external-html' DATA-JDK=ReadOnlyMap DATA-FILE-ID=INTERFACES>
 * 
 * @param <K> the type of keys maintained by this map
 * @param <V> the type of mapped values
 */
@Torello.JavaDoc.JDHeaderBackgroundImg(EmbedTagFileID="JDHBI_INTERFACE")
public interface ReadOnlyMap<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='ReadOnlyCollection.html#optional-restrictions'>optional-restrictions</A>)
     * 
     * @throws NullPointerException if the specified key is null and this map does not permit null
     * keys (<A HREF='ReadOnlyCollection.html#optional-restrictions'>optional-restrictions</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='ReadOnlyCollection.html#optional-restrictions'>optional-restrictions</A>)
     * 
     * @throws NullPointerException if the specified value is null and this map does not permit
     * null values
     * (<A HREF='ReadOnlyCollection.html#optional-restrictions'>optional-restrictions</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.
     * 
     * <BR /><BR />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.)
     *
     * <BR /><BR />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='ReadOnlyCollection.html#optional-restrictions'>optional-restrictions</A>)
     * 
     * @throws NullPointerException if the specified key is null and this map does not permit null
     * keys (<A HREF='ReadOnlyCollection.html#optional-restrictions'>optional-restrictions</A>)
     */
    V get(Object key);


    // ********************************************************************************************
    // ********************************************************************************************
    // Views
    // ********************************************************************************************
    // ********************************************************************************************


    /**
     * Returns a {@link ReadOnlySet} 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.
     * 
     * @return a set view of the keys contained in this map
     */
    ReadOnlySet<K> keySet();

    /**
     * Returns a {@link ReadOnlyCollection} view of the values contained in this map.
     * @return a collection view of the values contained in this map
     */
    ReadOnlyCollection<V> values();

    /**
     * Returns a {@link ReadOnlySet} view of the mappings contained in this map.
     * @return a set view of the mappings contained in this map
     */
    ReadOnlySet<ReadOnlyMap.Entry<K, V>> entrySet();

    /**
     * A map entry (key-value pair). 
     * 
     * <BR /><BR />An Entry may also be obtained from a map's entry-set view by other means, for
     * example, using the
     * {@link ReadOnlySet#parallelStream parallelStream},
     * {@link ReadOnlySet#stream stream},
     * {@link ReadOnlySet#spliterator spliterator}
     * methods, any of the
     * {@link ReadOnlySet#toArray toArray}
     * overloads, or by copying the entry-set view into another collection.
     * 
     * <BR /><BR />In addition, an Entry may be obtained directly from a map, for example via calls
     * to methods directly on the {@link ReadOnlyNavigableMap} interface.
     * 
     * @param <K> the type of the key
     * @param <V> the type of the value
     *
     * @see ReadOnlyMap#entrySet()
     */
    interface Entry<K, V>
    {
        /**
         * Returns the key corresponding to this entry.
         * @return the key corresponding to this entry
         */
        K getKey();

        /**
         * Returns the value corresponding to this entry.
         * @return the value corresponding to this entry
         */
        V getValue();

        /**
         * 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
         * 
         * <BR /><DIV CLASS=SNIP>{@code
         * (e1.getKey()==null
         *      ? e2.getKey()==null
         *      : e1.getKey().equals(e2.getKey()))
         * &amp;&amp;
         * (e1.getValue()==null
         *      ? e2.getValue()==null
         *      : e1.getValue().equals(e2.getValue()))
         * }</DIV>
         * 
         * <BR /><BR />This ensures that the {@code equals} method works properly across different
         * implementations of the {@code ReadOnlyMap.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:
         * 
         * <BR /><DIV CLASS=SNIP>{@code
         * (e.getKey()==null   ? 0 : e.getKey().hashCode()) ^
         * (e.getValue()==null ? 0 : e.getValue().hashCode())
         * }</DIV>
         * 
         * <BR /><BR />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 #equals(Object)
         */
        int hashCode();

        /**
         * Returns a comparator that compares {@link ReadOnlyMap.Entry} in natural order on key.
         *
         * <BR /><BR />The returned comparator is serializable and throws
         * {@code 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 ReadOnlyMap.Entry} in natural order on key.
         */
        public static <K extends Comparable<? super K>, V>
            Comparator<ReadOnlyMap.Entry<K, V>>
            comparingByKey()
        {
            return (Comparator<ReadOnlyMap.Entry<K, V>> & Serializable)
                (c1, c2) -> c1.getKey().compareTo(c2.getKey());
        }

        /**
         * Returns a comparator that compares {@link ReadOnlyMap.Entry} in natural order on value.
         *
         * <BR /><BR />The returned comparator is serializable and throws
         * {@code NullPointerException} when comparing an entry with null values.
         *
         * @param <K> the type of the map keys
         * @param <V> the {@code Comparable} type of the map values
         * @return a comparator that compares {@link ReadOnlyMap.Entry} in natural order on value.
         * @see Comparable
         */
        public static <K, V extends Comparable<? super V>>
            Comparator<ReadOnlyMap.Entry<K, V>>
            comparingByValue()
        {
            return (Comparator<ReadOnlyMap.Entry<K, V>> & Serializable)
                (c1, c2) -> c1.getValue().compareTo(c2.getValue());
        }

        /**
         * Returns a comparator that compares {@link ReadOnlyMap.Entry} by key using the given
         * {@code Comparator}.
         *
         * <BR /><BR />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 {@code Comparator}
         * @return a comparator that compares {@link ReadOnlyMap.Entry} by the key.
         */
        public static <K, V>
            Comparator<ReadOnlyMap.Entry<K, V>>
            comparingByKey(Comparator<? super K> cmp)
        {
            Objects.requireNonNull(cmp);
            return (Comparator<ReadOnlyMap.Entry<K, V>> & Serializable)
                (c1, c2) -> cmp.compare(c1.getKey(), c2.getKey());
        }

        /**
         * Returns a comparator that compares {@link ReadOnlyMap.Entry} by value using the given
         * {@code Comparator}.
         * 
         * <BR /><BR />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 ReadOnlyMap.Entry} by the value.
         */
        public static <K, V>
            Comparator<ReadOnlyMap.Entry<K, V>>
            comparingByValue(Comparator<? super V> cmp)
        {
            Objects.requireNonNull(cmp);
            return (Comparator<ReadOnlyMap.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 {@code Object.hashCode}.
     *
     * @return the hash code value for this map
     * @see ReadOnlyMap.Entry#hashCode()
     * @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.
     *
     * @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='ReadOnlyCollection.html#optional-restrictions'>optional-restrictions</A>)
     * 
     * @throws NullPointerException if the specified key is null and this map does not permit null
     * keys 
     * (<A HREF='ReadOnlyCollection.html#optional-restrictions'>optional-restrictions</A>)
     */
    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.
     * 
     * <BR /><BR />The default implementation is equivalent to, for this {@code map}:
     * 
     * <BR /><DIV CLASS=SNIP>{@code
     * for (ReadOnlyMap.Entry<K, V> entry : map.entrySet())
     *     action.accept(entry.getKey(), entry.getValue());
     * }</DIV>
     * 
     * <BR /><BR />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
     */
    default void forEach(BiConsumer<? super K, ? super V> action)
    {
        Objects.requireNonNull(action);

        for (ReadOnlyMap.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);

                throw new Torello.Java.UnreachableError();
            }

            action.accept(k, v);
        }
    }

    /**
     * Copies the contents of {@code 'this'} ReadOnlyMap into the user-provided {@code 'map'}.
     * Utilizes the {@code java.util.Map} method {@code put(K key, V value)}.
     * 
     * @param map Any instance of java.util.Map
     * @see #forEach(BiConsumer)
     */
    default void copyIntoMap(Map<? super K, ? super V> map)
    { this.forEach((K k, V v) -> map.put(k, v)); }


    // ********************************************************************************************
    // ********************************************************************************************
    // MAP-KEYS: contains - using Var-Args Arrays
    // ********************************************************************************************
    // ********************************************************************************************


    /**
     * Checks to ensure that {@code 'this'} instance of {@code ReadOnlyMap}
     * <B STYLE='color: red;'>contains a matching key for every one of the elements</B> in
     * Var-Args Parameter {@code 'elements'}
     * 
     * @param elements a list of elements
     * 
     * @return {@code TRUE} If and only if {@code 'this'} instance' {@code 'keySet()'} contains
     * every element in {@code 'elements'}
     */
    default boolean containsKeyAND(Object... elements)
    {
        ReadOnlySet<K> keys = this.keySet();
        for (Object elem : elements) if (! keys.contains(elem)) return false;
        return true;
    }

    /**
     * Checks to ensure that {@code 'this'} instance of {@code ReadOnlyMap}
     * <B STYLE='color: red;'>does not contain any key that matches any of the elements</B> in
     * Var-Args Parameter {@code 'elements'}
     * 
     * @param elements a list of elements
     * 
     * @return {@code TRUE} If and only if {@code 'this'} instance' {@code 'keySet()'} contains
     * none of the elements in {@code 'elements'}
     */
    default boolean containsKeyNAND(Object... elements)
    {
        ReadOnlySet<K> keys = this.keySet();
        for (Object elem : elements) if (keys.contains(elem)) return false;
        return true;
    }

    /**
     * Checks to ensure that {@code 'this'} instance of {@code ReadOnlyMap}
     * <B STYLE='color: red;'>contains at least one key that matches at least one element</B> in
     * Var-Args Parameter {@code 'elements'}
     * 
     * @param elements a list of elements
     * 
     * @return {@code TRUE} If and only if {@code 'this'} instance' {@code 'keySet()'} contains
     * one or more of the elements in {@code 'elements'}
     */
    default boolean containsKeyOR(Object... elements)
    {
        ReadOnlySet<K> keys = this.keySet();
        for (Object elem : elements) if (keys.contains(elem)) return true;
        return false;
    }

    /**
     * Checks to ensure that {@code 'this'} instance of {@code ReadOnlyMap}
     * <B STYLE='color: red;'>contains exactly one key that matches an element</B> in Var-Args
     * Parameter {@code 'elements'}
     * 
     * @param elements a list of elements
     * 
     * @return {@code TRUE} If and only if {@code 'this'} instance' {@code 'keySet()'} contains
     * precisely one element that is also in {@code 'elements'}
     */
    default boolean containsKeyXOR(Object... elements)
    {
        ReadOnlySet<K>  keys    = this.keySet();
        boolean         found   = false;

        for (Object elem : elements)

            if (keys.contains(elem))
            {
                if (found) return false;
                else found = true;
            }

        return found;
    }


    // ********************************************************************************************
    // ********************************************************************************************
    // MAP-KEYS: contains - using java.lang.Iterable
    // ********************************************************************************************
    // ********************************************************************************************


    /**
     * Checks to ensure that {@code 'this'} instance of {@code ReadOnlyMap}
     * <B STYLE='color: red;'>contains a matching key for every one of the elements</B> in
     * {@code Iterable} parameter {@code 'i'}.
     * 
     * @param i any Java {@code Iterable}
     * 
     * @return {@code TRUE} If and only if {@code 'this'} instance' {@code 'keySet()'} contains
     * every element in {@code 'i'}
     */
    default boolean containsKeyAND(Iterable<?> i)
    {
        ReadOnlySet<K> keys = this.keySet();
        for (Object o: i) if (! keys.contains(o)) return false;
        return true;
    }

    /**
     * Checks to ensure that {@code 'this'} instance of {@code ReadOnlyMap}
     * <B STYLE='color: red;'>does not contain any key that matches any of the elements</B> in
     * {@code Iterable} parameter {@code 'i'}
     *
     * @param i any Java {@code Iterable}
     * 
     * @return {@code TRUE} If and only if {@code 'this'} instance' {@code 'keySet()'} contains
     * none of the elements in {@code 'i'}
     */
    default boolean containsKeyNAND(Iterable<?> i)
    {
        ReadOnlySet<K> keys = this.keySet();
        for (Object o: i) if (keys.contains(o)) return false;
        return true;
    }

    /**
     * Checks to ensure that {@code 'this'} instance of {@code ReadOnlyMap}
     * <B STYLE='color: red;'>contains at least one key that matches at least one element</B> in
     * {@code Iterable} parameter {@code 'i'}
     *
     * @param i any Java {@code Iterable}
     * 
     * @return {@code TRUE} If and only if {@code 'this'} instance' {@code 'keySet()'} contains
     * one or more of the elements in {@code 'i'}
     */
    default boolean containsKeyOR(Iterable<?> i)
    {
        ReadOnlySet<K> keys = this.keySet();
        for (Object o: i) if (keys.contains(o)) return true;
        return false;
    }

    /**
     * Checks to ensure that {@code 'this'} instance of {@code ReadOnlyMap}
     * <B STYLE='color: red;'>contains exactly one key that matches an element</B> in 
     * {@code Iterable} parameter {@code 'i'}
     *
     * @param i any Java {@code Iterable}
     *  
     * @return {@code TRUE} If and only if {@code 'this'} instance' {@code 'keySet()'} contains
     * precisely one element that is also in {@code 'i'}
     */
    default boolean containsKeyXOR(Iterable<?> i)
    {
        ReadOnlySet<K>  keys    = this.keySet();
        boolean         found   = false;

        for (Object o: i)

            if (keys.contains(o))
            {
                if (found) return false;
                else found = true;
            }

        return found;
    }


    // ********************************************************************************************
    // ********************************************************************************************
    // MAP-VALUES: contains - using Var-Args Arrays
    // ********************************************************************************************
    // ********************************************************************************************


    /**
     * Checks to ensure that {@code 'this'} instance of {@code ReadOnlyMap}
     * <B STYLE='color: red;'>contains a matching value for every one of the elements</B> in
     * Var-Args Parameter {@code 'elements'}
     * 
     * @param elements a list of elements
     * 
     * @return {@code TRUE} If and only if {@code 'this'} instance' {@code 'values()'} contains
     * every element in {@code 'elements'}
     */
    default boolean containsValueAND(Object... elements)
    {
        ReadOnlyCollection<V> values = this.values();
        for (Object elem : elements) if (! values.contains(elem)) return false;
        return true;
    }

    /**
     * Checks to ensure that {@code 'this'} instance of {@code ReadOnlyMap}
     * <B STYLE='color: red;'>does not contain any value that matches any of the elements</B> in
     * Var-Args Parameter {@code 'elements'}
     * 
     * @param elements a list of elements
     * 
     * @return {@code TRUE} If and only if {@code 'this'} instance' {@code 'values()'} contains
     * none of the elements in {@code 'elements'}
     */
    default boolean containsValueNAND(Object... elements)
    {
        ReadOnlyCollection<V> values = this.values();
        for (Object elem : elements) if (values.contains(elem)) return false;
        return true;
    }

    /**
     * Checks to ensure that {@code 'this'} instance of {@code ReadOnlyMap}
     * <B STYLE='color: red;'>contains at least one value that matches at least one element</B> in
     * Var-Args Parameter {@code 'elements'}
     * 
     * @param elements a list of elements
     * 
     * @return {@code TRUE} If and only if {@code 'this'} instance' {@code 'values()'} contains
     * one or more of the elements in {@code 'elements'}
     */
    default boolean containsValueOR(Object... elements)
    {
        ReadOnlyCollection<V> values = this.values();
        for (Object elem : elements) if (values.contains(elem)) return true;
        return false;
    }

    /**
     * Checks to ensure that {@code 'this'} instance of {@code ReadOnlyMap}
     * <B STYLE='color: red;'>contains exactly one value that matches an element</B> in Var-Args
     * Parameter {@code 'elements'}
     * 
     * @param elements a list of elements
     * 
     * @return {@code TRUE} If and only if {@code 'this'} instance' {@code 'values()'} contains
     * precisely one element that is also in {@code 'elements'}
     */
    default boolean containsValueXOR(Object... elements)
    {
        ReadOnlyCollection<V>   values  = this.values();
        boolean                 found   = false;

        for (Object elem : elements)

            if (values.contains(elem))
            {
                if (found) return false;
                else found = true;
            }

        return found;
    }


    // ********************************************************************************************
    // ********************************************************************************************
    // MAP-VALUES: contains - using java.lang.Iterable
    // ********************************************************************************************
    // ********************************************************************************************


    /**
     * Checks to ensure that {@code 'this'} instance of {@code ReadOnlyMap}
     * <B STYLE='color: red;'>contains a matching value for every one of the elements</B> in
     * {@code Iterable} parameter {@code 'i'}
     * 
     * @param i any Java {@code Iterable}
     * 
     * @return {@code TRUE} If and only if {@code 'this'} instance' {@code 'values()'} contains
     * every element in {@code 'i'}
     */
    default boolean containsValueAND(Iterable<?> i)
    {
        ReadOnlyCollection<V> values = this.values();
        for (Object o: i) if (! values.contains(o)) return false;
        return true;
    }

    /**
     * Checks to ensure that {@code 'this'} instance of {@code ReadOnlyMap}
     * <B STYLE='color: red;'>does not contain any value that matches any of the elements</B> in
     * {@code Iterable} parameter {@code 'i'}
     * 
     * @param i any Java {@code Iterable}
     * 
     * @return {@code TRUE} If and only if {@code 'this'} instance' {@code 'values()'} contains
     * none of the elements in {@code 'i'}
     */
    default boolean containsValueNAND(Iterable<?> i)
    {
        ReadOnlyCollection<V> values = this.values();
        for (Object o: i) if (values.contains(o)) return false;
        return true;
    }

    /**
     * Checks to ensure that {@code 'this'} instance of {@code ReadOnlyMap}
     * <B STYLE='color: red;'>contains at least one value that matches at least one element</B> in
     * {@code Iterable} parameter {@code 'i'}
     *
     * @param i any Java {@code Iterable}
     * 
     * @return {@code TRUE} If and only if {@code 'this'} instance' {@code 'values()'} contains
     * one or more of the elements in {@code 'i'}
     */
    default boolean containsValueOR(Iterable<?> i)
    {
        ReadOnlyCollection<V> values = this.values();
        for (Object o: i) if (values.contains(o)) return true;
        return false;
    }

    /**
     * Checks to ensure that {@code 'this'} instance of {@code ReadOnlyMap}
     * <B STYLE='color: red;'>contains exactly one value that matches an element</B> in 
     * {@code Iterable} parameter {@code 'i'}
     *
     * @param i any Java {@code Iterable}
     *  
     * @return {@code TRUE} If and only if {@code 'this'} instance' {@code 'values()'} contains
     * precisely one element that is also in {@code 'i'}
     */
    default boolean containsValueXOR(Iterable<?> i)
    {
        ReadOnlyCollection<V>   values  = this.values();
        boolean                 found   = false;

        for (Object o: i)

            if (values.contains(o))
            {
                if (found) return false;
                else found = true;
            }

        return found;
    }


    // ********************************************************************************************
    // ********************************************************************************************
    // "of" ...
    // ********************************************************************************************
    // ********************************************************************************************


    /**
     * Returns an unmodifiable map containing zero mappings.
     *
     * @param <K> the {@code Map}'s key type
     * @param <V> the {@code Map}'s value type
     * @return an empty {@code Map}
     */
    @SuppressWarnings("unchecked")
    static <K, V> ReadOnlyMap<K, V> of()
    { return InterfaceBuilder.toReadOnlyMap(Map.of()); }

    /**
     * Returns an unmodifiable map containing a single mapping.
     *
     * @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 {@link ReadOnlyMap} containing the specified mapping
     * @throws NullPointerException if the key or the value is {@code null}
     */
    static <K, V> ReadOnlyMap<K, V> of(K k1, V v1)
    { return InterfaceBuilder.toReadOnlyMap(Map.of(k1, v1)); }

    /**
     * Returns an unmodifiable map containing two mappings.
     *
     * @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 {@link ReadOnlyMap} containing the specified mappings
     * @throws IllegalArgumentException if the keys are duplicates
     * @throws NullPointerException if any key or value is {@code null}
     */
    static <K, V> ReadOnlyMap<K, V> of(K k1, V v1, K k2, V v2)
    { return InterfaceBuilder.toReadOnlyMap(Map.of(k1, v1, k2, v2)); }

    /**
     * Returns an unmodifiable map containing three mappings.
     *
     * @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 {@link ReadOnlyMap} containing the specified mappings
     * @throws IllegalArgumentException if there are any duplicate keys
     * @throws NullPointerException if any key or value is {@code null}
     */
    static <K, V> ReadOnlyMap<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3)
    { return InterfaceBuilder.toReadOnlyMap(Map.of(k1, v1, k2, v2, k3, v3)); }

    /**
     * Returns an unmodifiable map containing four mappings.
     *
     * @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 {@link ReadOnlyMap} containing the specified mappings
     * @throws IllegalArgumentException if there are any duplicate keys
     * @throws NullPointerException if any key or value is {@code null}
     */
    static <K, V> ReadOnlyMap<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4)
    { return InterfaceBuilder.toReadOnlyMap(Map.of(k1, v1, k2, v2, k3, v3, k4, v4)); }

    /**
     * Returns an unmodifiable map containing five mappings.
     *
     * @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 {@link ReadOnlyMap} containing the specified mappings
     * @throws IllegalArgumentException if there are any duplicate keys
     * @throws NullPointerException if any key or value is {@code null}
     *
     */
    static <K, V> ReadOnlyMap<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5)
    { return InterfaceBuilder.toReadOnlyMap(Map.of(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5)); }

    /**
     * Returns an unmodifiable map containing six mappings.
     *
     * @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 {@link ReadOnlyMap} containing the specified mappings
     * @throws IllegalArgumentException if there are any duplicate keys
     * @throws NullPointerException if any key or value is {@code null}
     */
    static <K, V> ReadOnlyMap<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 InterfaceBuilder.toReadOnlyMap
            (Map.of(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5, k6, v6));
    }

    /**
     * Returns an unmodifiable map containing seven mappings.
     * 
     * @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 {@link ReadOnlyMap} containing the specified mappings
     * @throws IllegalArgumentException if there are any duplicate keys
     * @throws NullPointerException if any key or value is {@code null}
     */
    static <K, V> ReadOnlyMap<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 InterfaceBuilder.toReadOnlyMap
            (Map.of(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5, k6, v6, k7, v7));
    }

    /**
     * Returns an unmodifiable map containing eight mappings.
     * 
     * @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 {@link ReadOnlyMap} containing the specified mappings
     * @throws IllegalArgumentException if there are any duplicate keys
     * @throws NullPointerException if any key or value is {@code null}
     */
    static <K, V> ReadOnlyMap<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 InterfaceBuilder.toReadOnlyMap
            (Map.of(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5, k6, v6, k7, v7, k8, v8));
    }

    /**
     * Returns an unmodifiable map containing nine mappings.
     * 
     * @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 {@link ReadOnlyMap} containing the specified mappings
     * @throws IllegalArgumentException if there are any duplicate keys
     * @throws NullPointerException if any key or value is {@code null}
     */
    static <K, V> ReadOnlyMap<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 InterfaceBuilder.toReadOnlyMap
            (Map.of(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5, k6, v6, k7, v7, k8, v8, k9, v9));
    }

    /**
     * Returns an unmodifiable map containing ten mappings.
     *
     * @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 {@link ReadOnlyMap} containing the specified mappings
     * @throws IllegalArgumentException if there are any duplicate keys
     * @throws NullPointerException if any key or value is {@code null}
     */
    static <K, V> ReadOnlyMap<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 InterfaceBuilder.toReadOnlyMap(
            Map.of(
                k1, v1, k2, v2, k3, v3, k4, v4, k5, v5, k6, v6,
                k7, v7, k8, v8, k9, v9, k10, v10
            ));
    }

    /**
     * Returns an unmodifiable map containing keys and values extracted from the given entries.
     * The entries themselves are not stored in the map.
     *
     * <BR /><BR />It is convenient to create the map entries using the
     * {@link ReadOnlyMap#entry ReadOnlyMap.entry()} method.  For example,
     *
     * <DIV CLASS=EXAMPLE>{@code
     * import static Torello.Java.ReadOnly.ReadOnlyMap.entry;
     *
     * ReadOnlyMap<Integer,String> map = ReadOnlyMap.ofEntries(
     *      entry(1, "a"),
     *      entry(2, "b"),
     *      entry(3, "c"),
     *      ...
     *      entry(26, "z"));
     * }</DIV>
     *
     * @param <K> the {@link ReadOnlyMap}'s key type
     * @param <V> the {@link ReadOnlyMap}'s value type
     * 
     * @param entries {@code ReadOnlyMap.Entry}s containing the keys and values from which the map
     * is populated
     * 
     * @return a {@link ReadOnlyMap} 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 ReadOnlyMap#entry Map.entry()
     */
    @SafeVarargs
    @SuppressWarnings("varargs")
    static <K, V>
        ReadOnlyMap<K, V>
        ofEntries
        (ReadOnlyMap.Entry<? extends K, ? extends V>... entries)
    {
        // *** Java-HTML: This arbitrarily uses TreeMap
        ROTreeMapBuilder<K, V> b = new ROTreeMapBuilder<>();

        for (ReadOnlyMap.Entry<? extends K, ? extends V> e : entries)
            b.put(e.getKey(), e.getValue());

        return b.build();
    }

    /**
     * Returns an unmodifiable {@link Entry} containing the given key and value.
     * These entries are suitable for populating {@code ReadOnlyMap} instances using the
     * {@link ReadOnlyMap#ofEntries ReadOnlyMap.ofEntries()} method.
     * 
     * @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 ReadOnlyMap#ofEntries Map.ofEntries()
     */
    static <K, V> ReadOnlyMap.Entry<K, V> entry(K k, V v)
    {
        // KeyValueHolder checks for nulls
        // return new KeyValueHolder<>(k, v);
        return new EntryImpl<>(Objects.requireNonNull(k), Objects.requireNonNull(v));
    }
}