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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

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 * accompanied this code).

 *

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package java.util;

import java.util.Map.Entry;

/**

 * This class provides a skeletal implementation of the {@code Map}

 * interface, to minimize the effort required to implement this interface.

 *

 * <p>To implement an unmodifiable map, the programmer needs only to extend this

 * class and provide an implementation for the {@code entrySet} method, which

 * returns a set-view of the map's mappings.  Typically, the returned set

 * will, in turn, be implemented atop {@code AbstractSet}.  This set should

 * not support the {@code add} or {@code remove} methods, and its iterator

 * should not support the {@code remove} method.

 *

 * <p>To implement a modifiable map, the programmer must additionally override

 * this class's {@code put} method (which otherwise throws an

 * {@code UnsupportedOperationException}), and the iterator returned by

 * {@code entrySet().iterator()} must additionally implement its

 * {@code remove} method.

 *

 * <p>The programmer should generally provide a void (no argument) and map

 * constructor, as per the recommendation in the {@code Map} interface

 * specification.

 *

 * <p>The documentation for each non-abstract method in this class describes its

 * implementation in detail.  Each of these methods may be overridden if the

 * map being implemented admits a more efficient implementation.

 *

 * <p>This class is a member of the

 * <a href="{@docRoot}/java.base/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

 * @author  Neal Gafter

 * @see Map

 * @see Collection

 * @since 1.2

 */

public abstract class AbstractMap<K,V> implements Map<K,V> {

    /**

     * Sole constructor.  (For invocation by subclass constructors, typically

     * implicit.)

     */

    protected AbstractMap() {

    }

    // Query Operations

    /**

     * {@inheritDoc}

     *

     * @implSpec

     * This implementation returns {@code entrySet().size()}.

     */

    public int size() {

        return entrySet().size();

    }

    /**

     * {@inheritDoc}

     *

     * @implSpec

     * This implementation returns {@code size() == 0}.

     */

    public boolean isEmpty() {

        return size() == 0;

    }

    /**

     * {@inheritDoc}

     *

     * @implSpec

     * This implementation iterates over {@code entrySet()} searching

     * for an entry with the specified value.  If such an entry is found,

     * {@code true} is returned.  If the iteration terminates without

     * finding such an entry, {@code false} is returned.  Note that this

     * implementation requires linear time in the size of the map.

     *

     * @throws ClassCastException   {@inheritDoc}

     * @throws NullPointerException {@inheritDoc}

     */

    public boolean containsValue(Object value) {

        Iterator<Entry<K,V>> i = entrySet().iterator();

        if (value==null) {

            while (i.hasNext()) {

                Entry<K,V> e = i.next();

                if (e.getValue()==null)

                    return true;

            }

        } else {

            while (i.hasNext()) {

                Entry<K,V> e = i.next();

                if (value.equals(e.getValue()))

                    return true;

            }

        }

        return false;

    }

    /**

     * {@inheritDoc}

     *

     * @implSpec

     * This implementation iterates over {@code entrySet()} searching

     * for an entry with the specified key.  If such an entry is found,

     * {@code true} is returned.  If the iteration terminates without

     * finding such an entry, {@code false} is returned.  Note that this

     * implementation requires linear time in the size of the map; many

     * implementations will override this method.

     *

     * @throws ClassCastException   {@inheritDoc}

     * @throws NullPointerException {@inheritDoc}

     */

    public boolean containsKey(Object key) {

        Iterator<Map.Entry<K,V>> i = entrySet().iterator();

        if (key==null) {

            while (i.hasNext()) {

                Entry<K,V> e = i.next();

                if (e.getKey()==null)

                    return true;

            }

        } else {

            while (i.hasNext()) {

                Entry<K,V> e = i.next();

                if (key.equals(e.getKey()))

                    return true;

            }

        }

        return false;

    }

    /**

     * {@inheritDoc}

     *

     * @implSpec

     * This implementation iterates over {@code entrySet()} searching

     * for an entry with the specified key.  If such an entry is found,

     * the entry's value is returned.  If the iteration terminates without

     * finding such an entry, {@code null} is returned.  Note that this

     * implementation requires linear time in the size of the map; many

     * implementations will override this method.

     *

     * @throws ClassCastException            {@inheritDoc}

     * @throws NullPointerException          {@inheritDoc}

     */

    public V get(Object key) {

        Iterator<Entry<K,V>> i = entrySet().iterator();

        if (key==null) {

            while (i.hasNext()) {

                Entry<K,V> e = i.next();

                if (e.getKey()==null)

                    return e.getValue();

            }

        } else {

            while (i.hasNext()) {

                Entry<K,V> e = i.next();

                if (key.equals(e.getKey()))

                    return e.getValue();

            }

        }

        return null;

    }

    // Modification Operations

    /**

     * {@inheritDoc}

     *

     * @implSpec

     * This implementation always throws an

     * {@code UnsupportedOperationException}.

     *

     * @throws UnsupportedOperationException {@inheritDoc}

     * @throws ClassCastException            {@inheritDoc}

     * @throws NullPointerException          {@inheritDoc}

     * @throws IllegalArgumentException      {@inheritDoc}

     */

    public V put(K key, V value) {

        throw new UnsupportedOperationException();

    }

    /**

     * {@inheritDoc}

     *

     * @implSpec

     * This implementation iterates over {@code entrySet()} searching for an

     * entry with the specified key.  If such an entry is found, its value is

     * obtained with its {@code getValue} operation, the entry is removed

     * from the collection (and the backing map) with the iterator's

     * {@code remove} operation, and the saved value is returned.  If the

     * iteration terminates without finding such an entry, {@code null} is

     * returned.  Note that this implementation requires linear time in the

     * size of the map; many implementations will override this method.

     *

     * <p>Note that this implementation throws an

     * {@code UnsupportedOperationException} if the {@code entrySet}

     * iterator does not support the {@code remove} method and this map

     * contains a mapping for the specified key.

     *

     * @throws UnsupportedOperationException {@inheritDoc}

     * @throws ClassCastException            {@inheritDoc}

     * @throws NullPointerException          {@inheritDoc}

     */

    public V remove(Object key) {

        Iterator<Entry<K,V>> i = entrySet().iterator();

        Entry<K,V> correctEntry = null;

        if (key==null) {

            while (correctEntry==null && i.hasNext()) {

                Entry<K,V> e = i.next();

                if (e.getKey()==null)

                    correctEntry = e;

            }

        } else {

            while (correctEntry==null && i.hasNext()) {

                Entry<K,V> e = i.next();

                if (key.equals(e.getKey()))

                    correctEntry = e;

            }

        }

        V oldValue = null;

        if (correctEntry !=null) {

            oldValue = correctEntry.getValue();

            i.remove();

        }

        return oldValue;

    }

    // Bulk Operations

    /**

     * {@inheritDoc}

     *

     * @implSpec

     * This implementation iterates over the specified map's

     * {@code entrySet()} collection, and calls this map's {@code put}

     * operation once for each entry returned by the iteration.

     *

     * <p>Note that this implementation throws an

     * {@code UnsupportedOperationException} if this map does not support

     * the {@code put} operation and the specified map is nonempty.

     *

     * @throws UnsupportedOperationException {@inheritDoc}

     * @throws ClassCastException            {@inheritDoc}

     * @throws NullPointerException          {@inheritDoc}

     * @throws IllegalArgumentException      {@inheritDoc}

     */

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

        for (Map.Entry<? extends K, ? extends V> e : m.entrySet())

            put(e.getKey(), e.getValue());

    }

    /**

     * {@inheritDoc}

     *

     * @implSpec

     * This implementation calls {@code entrySet().clear()}.

     *

     * <p>Note that this implementation throws an

     * {@code UnsupportedOperationException} if the {@code entrySet}

     * does not support the {@code clear} operation.

     *

     * @throws UnsupportedOperationException {@inheritDoc}

     */

    public void clear() {

        entrySet().clear();

    }

    // Views

    /**

     * Each of these fields are initialized to contain an instance of the

     * appropriate view the first time this view is requested.  The views are

     * stateless, so there's no reason to create more than one of each.

     *

     * <p>Since there is no synchronization performed while accessing these fields,

     * it is expected that java.util.Map view classes using these fields have

     * no non-final fields (or any fields at all except for outer-this). Adhering

     * to this rule would make the races on these fields benign.

     *

     * <p>It is also imperative that implementations read the field only once,

     * as in:

     *

     * <pre> {@code

     * public Set<K> keySet() {

     *   Set<K> ks = keySet;  // single racy read

     *   if (ks == null) {

     *     ks = new KeySet();

     *     keySet = ks;

     *   }

     *   return ks;

     * }

     *}</pre>

     */

    transient Set<K>        keySet;

    transient Collection<V> values;

    /**

     * {@inheritDoc}

     *

     * @implSpec

     * This implementation returns a set that subclasses {@link AbstractSet}.

     * The subclass's iterator method returns a "wrapper object" over this

     * map's {@code entrySet()} iterator.  The {@code size} method

     * delegates to this map's {@code size} method and the

     * {@code contains} method delegates to this map's

     * {@code containsKey} method.

     *

     * <p>The set is created the first time this method is called,

     * and returned in response to all subsequent calls.  No synchronization

     * is performed, so there is a slight chance that multiple calls to this

     * method will not all return the same set.

     */

    public Set<K> keySet() {

        Set<K> ks = keySet;

        if (ks == null) {

            ks = new AbstractSet<K>() {

                public Iterator<K> iterator() {

                    return new Iterator<K>() {

                        private Iterator<Entry<K,V>> i = entrySet().iterator();

                        public boolean hasNext() {

                            return i.hasNext();

                        }

                        public K next() {

                            return i.next().getKey();

                        }

                        public void remove() {

                            i.remove();

                        }

                    };

                }

                public int size() {

                    return AbstractMap.this.size();

                }

                public boolean isEmpty() {

                    return AbstractMap.this.isEmpty();

                }

                public void clear() {

                    AbstractMap.this.clear();

                }

                public boolean contains(Object k) {

                    return AbstractMap.this.containsKey(k);

                }

            };

            keySet = ks;

        }

        return ks;

    }

    /**

     * {@inheritDoc}

     *

     * @implSpec

     * This implementation returns a collection that subclasses {@link

     * AbstractCollection}.  The subclass's iterator method returns a

     * "wrapper object" over this map's {@code entrySet()} iterator.

     * The {@code size} method delegates to this map's {@code size}

     * method and the {@code contains} method delegates to this map's

     * {@code containsValue} method.

     *

     * <p>The collection is created the first time this method is called, and

     * returned in response to all subsequent calls.  No synchronization is

     * performed, so there is a slight chance that multiple calls to this

     * method will not all return the same collection.

     */

    public Collection<V> values() {

        Collection<V> vals = values;

        if (vals == null) {

            vals = new AbstractCollection<V>() {

                public Iterator<V> iterator() {

                    return new Iterator<V>() {

                        private Iterator<Entry<K,V>> i = entrySet().iterator();

                        public boolean hasNext() {

                            return i.hasNext();

                        }

                        public V next() {

                            return i.next().getValue();

                        }

                        public void remove() {

                            i.remove();

                        }

                    };

                }

                public int size() {

                    return AbstractMap.this.size();

                }

                public boolean isEmpty() {

                    return AbstractMap.this.isEmpty();

                }

                public void clear() {

                    AbstractMap.this.clear();

                }

                public boolean contains(Object v) {

                    return AbstractMap.this.containsValue(v);

                }

            };

            values = vals;

        }

        return vals;

    }

    public abstract Set<Entry<K,V>> entrySet();

    // 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.

     *

     * @implSpec

     * This implementation first checks if the specified object is this map;

     * if so it returns {@code true}.  Then, it checks if the specified

     * object is a map whose size is identical to the size of this map; if

     * not, it returns {@code false}.  If so, it iterates over this map's

     * {@code entrySet} collection, and checks that the specified map

     * contains each mapping that this map contains.  If the specified map

     * fails to contain such a mapping, {@code false} is returned.  If the

     * iteration completes, {@code true} is returned.

     *

     * @param o object to be compared for equality with this map

     * @return {@code true} if the specified object is equal to this map

     */

    public boolean equals(Object o) {

        if (o == this)

            return true;

        if (!(o instanceof Map))

            return false;

        Map<?,?> m = (Map<?,?>) o;

        if (m.size() != size())

            return false;

        try {

            for (Entry<K, V> e : entrySet()) {

                K key = e.getKey();

                V value = e.getValue();

                if (value == null) {

                    if (!(m.get(key) == null && m.containsKey(key)))

                        return false;

                } else {

                    if (!value.equals(m.get(key)))

                        return false;

                }

            }

        } catch (ClassCastException unused) {

            return false;

        } catch (NullPointerException unused) {

            return false;

        }

        return true;

    }

    /**

     * 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}.

     *

     * @implSpec