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 * Copyright (c) 2003, 2018, 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,

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 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

package java.util;

/**

 * A specialized {@link Map} implementation for use with enum type keys.  All

 * of the keys in an enum map must come from a single enum type that is

 * specified, explicitly or implicitly, when the map is created.  Enum maps

 * are represented internally as arrays.  This representation is extremely

 * compact and efficient.

 *

 * <p>Enum maps are maintained in the <i>natural order</i> of their keys

 * (the order in which the enum constants are declared).  This is reflected

 * in the iterators returned by the collections views ({@link #keySet()},

 * {@link #entrySet()}, and {@link #values()}).

 *

 * <p>Iterators returned by the collection views are <i>weakly consistent</i>:

 * they will never throw {@link ConcurrentModificationException} and they may

 * or may not show the effects of any modifications to the map that occur while

 * the iteration is in progress.

 *

 * <p>Null keys are not permitted.  Attempts to insert a null key will

 * throw {@link NullPointerException}.  Attempts to test for the

 * presence of a null key or to remove one will, however, function properly.

 * Null values are permitted.

 * <P>Like most collection implementations {@code EnumMap} is not

 * synchronized. If multiple threads access an enum map concurrently, and at

 * least one of the threads modifies the map, it should be synchronized

 * externally.  This is typically accomplished by synchronizing on some

 * object that naturally encapsulates the enum map.  If no such object exists,

 * the map should be "wrapped" using the {@link Collections#synchronizedMap}

 * method.  This is best done at creation time, to prevent accidental

 * unsynchronized access:

 *

 * <pre>

 *     Map<EnumKey, V> m

 *         = Collections.synchronizedMap(new EnumMap<EnumKey, V>(...));

 * </pre>

 *

 * <p>Implementation note: All basic operations execute in constant time.

 * They are likely (though not guaranteed) to be faster than their

 * {@link HashMap} counterparts.

 *

 * <p>This class is a member of the

 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">

 * Java Collections Framework</a>.

 *

 * @author Josh Bloch

 * @see EnumSet

 * @since 1.5

 */

public class EnumMap<K extends Enum<K>, V> extends AbstractMap<K, V>

    implements java.io.Serializable, Cloneable

{

    /**

     * The {@code Class} object for the enum type of all the keys of this map.

     *

     * @serial

     */

    private final Class<K> keyType;

    /**

     * All of the values comprising K.  (Cached for performance.)

     */

    private transient K[] keyUniverse;

    /**

     * Array representation of this map.  The ith element is the value

     * to which universe[i] is currently mapped, or null if it isn't

     * mapped to anything, or NULL if it's mapped to null.

     */

    private transient Object[] vals;

    /**

     * The number of mappings in this map.

     */

    private transient int size = 0;

    /**

     * Distinguished non-null value for representing null values.

     */

    private static final Object NULL = new Object() {

        public int hashCode() {

            return 0;

        }

        public String toString() {

            return "java.util.EnumMap.NULL";

        }

    };

    private Object maskNull(Object value) {

        return (value == null ? NULL : value);

    }

    @SuppressWarnings("unchecked")

    private V unmaskNull(Object value) {

        return (V)(value == NULL ? null : value);

    }

    /**

     * Creates an empty enum map with the specified key type.

     *

     * @param keyType the class object of the key type for this enum map

     * @throws NullPointerException if {@code keyType} is null

     */

    public EnumMap(Class<K> keyType) {

        this.keyType = keyType;

        keyUniverse = getKeyUniverse(keyType);

        vals = new Object[keyUniverse.length];

    }

    /**

     * Creates an enum map with the same key type as the specified enum

     * map, initially containing the same mappings (if any).

     *

     * @param m the enum map from which to initialize this enum map

     * @throws NullPointerException if {@code m} is null

     */

    public EnumMap(EnumMap<K, ? extends V> m) {

        keyType = m.keyType;

        keyUniverse = m.keyUniverse;

        vals = m.vals.clone();

        size = m.size;

    }

    /**

     * Creates an enum map initialized from the specified map.  If the

     * specified map is an {@code EnumMap} instance, this constructor behaves

     * identically to {@link #EnumMap(EnumMap)}.  Otherwise, the specified map

     * must contain at least one mapping (in order to determine the new

     * enum map's key type).

     *

     * @param m the map from which to initialize this enum map

     * @throws IllegalArgumentException if {@code m} is not an

     *     {@code EnumMap} instance and contains no mappings

     * @throws NullPointerException if {@code m} is null

     */

    public EnumMap(Map<K, ? extends V> m) {

        if (m instanceof EnumMap) {

            EnumMap<K, ? extends V> em = (EnumMap<K, ? extends V>) m;

            keyType = em.keyType;

            keyUniverse = em.keyUniverse;

            vals = em.vals.clone();

            size = em.size;

        } else {

            if (m.isEmpty())

                throw new IllegalArgumentException("Specified map is empty");

            keyType = m.keySet().iterator().next().getDeclaringClass();

            keyUniverse = getKeyUniverse(keyType);

            vals = new Object[keyUniverse.length];

            putAll(m);

        }

    }

    // Query Operations

    /**

     * Returns the number of key-value mappings in this map.

     *

     * @return the number of key-value mappings in this map

     */

    public int size() {

        return size;

    }

    /**

     * Returns {@code true} if this map maps one or more keys to the

     * specified value.

     *

     * @param value the value whose presence in this map is to be tested

     * @return {@code true} if this map maps one or more keys to this value

     */

    public boolean containsValue(Object value) {

        value = maskNull(value);

        for (Object val : vals)

            if (value.equals(val))

                return true;

        return false;

    }

    /**

     * Returns {@code true} if this map contains a mapping for the specified

     * key.

     *

     * @param key the key whose presence in this map is to be tested

     * @return {@code true} if this map contains a mapping for the specified

     *            key

     */

    public boolean containsKey(Object key) {

        return isValidKey(key) && vals[((Enum<?>)key).ordinal()] != null;

    }

    private boolean containsMapping(Object key, Object value) {

        return isValidKey(key) &&

            maskNull(value).equals(vals[((Enum<?>)key).ordinal()]);

    }

    /**

     * 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 (key == k)},

     * then this method returns {@code v}; otherwise it returns

     * {@code null}.  (There can be at most one such mapping.)

     *

     * <p>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.

     */

    public V get(Object key) {

        return (isValidKey(key) ?

                unmaskNull(vals[((Enum<?>)key).ordinal()]) : null);

    }

    // Modification Operations

    /**

     * Associates the specified value with the specified key in this map.

     * If the map previously contained a mapping for this key, the old

     * value is replaced.

     *

     * @param key the key with which the specified value is to be associated

     * @param value the value to be associated with the specified key

     *

     * @return the previous value associated with specified key, or

     *     {@code null} if there was no mapping for key.  (A {@code null}

     *     return can also indicate that the map previously associated

     *     {@code null} with the specified key.)

     * @throws NullPointerException if the specified key is null

     */

    public V put(K key, V value) {

        typeCheck(key);

        int index = key.ordinal();

        Object oldValue = vals[index];

        vals[index] = maskNull(value);

        if (oldValue == null)

            size++;

        return unmaskNull(oldValue);

    }

    /**

     * Removes the mapping for this key from this map if present.

     *

     * @param key the key whose mapping is to be removed from the map

     * @return the previous value associated with specified key, or

     *     {@code null} if there was no entry for key.  (A {@code null}

     *     return can also indicate that the map previously associated

     *     {@code null} with the specified key.)

     */

    public V remove(Object key) {

        if (!isValidKey(key))

            return null;

        int index = ((Enum<?>)key).ordinal();

        Object oldValue = vals[index];

        vals[index] = null;

        if (oldValue != null)

            size--;

        return unmaskNull(oldValue);

    }

    private boolean removeMapping(Object key, Object value) {

        if (!isValidKey(key))

            return false;

        int index = ((Enum<?>)key).ordinal();

        if (maskNull(value).equals(vals[index])) {

            vals[index] = null;

            size--;

            return true;

        }

        return false;

    }

    /**

     * Returns true if key is of the proper type to be a key in this

     * enum map.

     */

    private boolean isValidKey(Object key) {

        if (key == null)

            return false;

        // Cheaper than instanceof Enum followed by getDeclaringClass

        Class<?> keyClass = key.getClass();

        return keyClass == keyType || keyClass.getSuperclass() == keyType;

    }

    // Bulk Operations

    /**

     * Copies all of the mappings from the specified map to this map.

     * These mappings will replace any mappings that this map had for

     * any of the keys currently in the specified map.

     *

     * @param m the mappings to be stored in this map

     * @throws NullPointerException the specified map is null, or if

     *     one or more keys in the specified map are null

     */

    public void putAll(Map<? extends K, ? extends V> m) {

        if (m instanceof EnumMap) {

            EnumMap<?, ?> em = (EnumMap<?, ?>)m;

            if (em.keyType != keyType) {

                if (em.isEmpty())

                    return;

                throw new ClassCastException(em.keyType + " != " + keyType);

            }

            for (int i = 0; i < keyUniverse.length; i++) {

                Object emValue = em.vals[i];

                if (emValue != null) {

                    if (vals[i] == null)

                        size++;

                    vals[i] = emValue;

                }

            }

        } else {

            super.putAll(m);

        }

    }

    /**

     * Removes all mappings from this map.

     */

    public void clear() {

        Arrays.fill(vals, null);

        size = 0;

    }

    // Views

    /**

     * This field is initialized to contain an instance of the entry set

     * view the first time this view is requested.  The view is stateless,

     * so there's no reason to create more than one.

     */

    private transient Set<Map.Entry<K,V>> entrySet;

    /**

     * Returns a {@link Set} view of the keys contained in this map.

     * The returned set obeys the general contract outlined in

     * {@link Map#keySet()}.  The set's iterator will return the keys

     * in their natural order (the order in which the enum constants

     * are declared).

     *

     * @return a set view of the keys contained in this enum map

     */

    public Set<K> keySet() {

        Set<K> ks = keySet;

        if (ks == null) {

            ks = new KeySet();

            keySet = ks;

        }

        return ks;

    }

    private class KeySet extends AbstractSet<K> {

        public Iterator<K> iterator() {

            return new KeyIterator();

        }

        public int size() {

            return size;

        }

        public boolean contains(Object o) {

            return containsKey(o);

        }

        public boolean remove(Object o) {

            int oldSize = size;

            EnumMap.this.remove(o);

            return size != oldSize;

        }

        public void clear() {

            EnumMap.this.clear();

        }

    }

    /**

     * Returns a {@link Collection} view of the values contained in this map.

     * The returned collection obeys the general contract outlined in

     * {@link Map#values()}.  The collection's iterator will return the

     * values in the order their corresponding keys appear in map,

     * which is their natural order (the order in which the enum constants

     * are declared).

     *

     * @return a collection view of the values contained in this map

     */

    public Collection<V> values() {

        Collection<V> vs = values;

        if (vs == null) {

            vs = new Values();

            values = vs;

        }

        return vs;

    }

    private class Values extends AbstractCollection<V> {

        public Iterator<V> iterator() {

            return new ValueIterator();

        }

        public int size() {

            return size;

        }

        public boolean contains(Object o) {

            return containsValue(o);

        }

        public boolean remove(Object o) {

            o = maskNull(o);

            for (int i = 0; i < vals.length; i++) {

                if (o.equals(vals[i])) {

                    vals[i] = null;

                    size--;

                    return true;

                }

            }

            return false;

        }

        public void clear() {

            EnumMap.this.clear();

        }

    }

    /**

     * Returns a {@link Set} view of the mappings contained in this map.

     * The returned set obeys the general contract outlined in

     * {@link Map#keySet()}.  The set's iterator will return the

     * mappings in the order their keys appear in map, which is their

     * natural order (the order in which the enum constants are declared).

     *

     * @return a set view of the mappings contained in this enum map

     */

    public Set<Map.Entry<K,V>> entrySet() {

        Set<Map.Entry<K,V>> es = entrySet;

        if (es != null)

            return es;

        else

            return entrySet = new EntrySet();

    }

    private class EntrySet extends AbstractSet<Map.Entry<K,V>> {

        public Iterator<Map.Entry<K,V>> iterator() {

            return new EntryIterator();

        }

        public boolean contains(Object o) {

            if (!(o instanceof Map.Entry))

                return false;

            Map.Entry<?,?> entry = (Map.Entry<?,?>)o;

            return containsMapping(entry.getKey(), entry.getValue());

        }

        public boolean remove(Object o) {

            if (!(o instanceof Map.Entry))

                return false;

            Map.Entry<?,?> entry = (Map.Entry<?,?>)o;

            return removeMapping(entry.getKey(), entry.getValue());

        }

        public int size() {

            return size;

        }

        public void clear() {

            EnumMap.this.clear();

        }

        public Object[] toArray() {

            return fillEntryArray(new Object[size]);

        }

        @SuppressWarnings("unchecked")

        public <T> T[] toArray(T[] a) {

            int size = size();

            if (a.length < size)

                a = (T[])java.lang.reflect.Array

                    .newInstance(a.getClass().getComponentType(), size);

            if (a.length > size)

                a[size] = null;

            return (T[]) fillEntryArray(a);

        }

        private Object[] fillEntryArray(Object[] a) {

            int j = 0;

            for (int i = 0; i < vals.length; i++)

                if (vals[i] != null)

                    a[j++] = new AbstractMap.SimpleEntry<>(

                        keyUniverse[i], unmaskNull(vals[i]));

            return a;

        }

    }

    private abstract class EnumMapIterator<T> implements Iterator<T> {

        // Lower bound on index of next element to return

        int index = 0;