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 * 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

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 */

package java.util;

import java.util.Map.Entry;

/**

 * This class provides a skeletal implementation of the <tt>Map</tt>

 * 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 <tt>entrySet</tt> method, which

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

 * will, in turn, be implemented atop <tt>AbstractSet</tt>.  This set should

 * not support the <tt>add</tt> or <tt>remove</tt> methods, and its iterator

 * should not support the <tt>remove</tt> method.

 *

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

 * this class's <tt>put</tt> method (which otherwise throws an

 * <tt>UnsupportedOperationException</tt>), and the iterator returned by

 * <tt>entrySet().iterator()</tt> must additionally implement its

 * <tt>remove</tt> method.

 *

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

 * constructor, as per the recommendation in the <tt>Map</tt> 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}/../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

 * @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}

     *

     * <p>This implementation returns <tt>entrySet().size()</tt>.

     */

    public int size() {

        return entrySet().size();

    }

    /**

     * {@inheritDoc}

     *

     * <p>This implementation returns <tt>size() == 0</tt>.

     */

    public boolean isEmpty() {

        return size() == 0;

    }

    /**

     * {@inheritDoc}

     *

     * <p>This implementation iterates over <tt>entrySet()</tt> searching

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

     * <tt>true</tt> is returned.  If the iteration terminates without

     * finding such an entry, <tt>false</tt> 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}

     *

     * <p>This implementation iterates over <tt>entrySet()</tt> searching

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

     * <tt>true</tt> is returned.  If the iteration terminates without

     * finding such an entry, <tt>false</tt> 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}

     *

     * <p>This implementation iterates over <tt>entrySet()</tt> 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, <tt>null</tt> 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}

     *

     * <p>This implementation always throws an

     * <tt>UnsupportedOperationException</tt>.

     *

     * @throws UnsupportedOperationException {@inheritDoc}

     * @throws ClassCastException            {@inheritDoc}

     * @throws NullPointerException          {@inheritDoc}

     * @throws IllegalArgumentException      {@inheritDoc}

     */

    public V put(K key, V value) {

        throw new UnsupportedOperationException();

    }

    /**

     * {@inheritDoc}

     *

     * <p>This implementation iterates over <tt>entrySet()</tt> searching for an

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

     * obtained with its <tt>getValue</tt> operation, the entry is removed

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

     * <tt>remove</tt> operation, and the saved value is returned.  If the

     * iteration terminates without finding such an entry, <tt>null</tt> 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

     * <tt>UnsupportedOperationException</tt> if the <tt>entrySet</tt>

     * iterator does not support the <tt>remove</tt> 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}

     *

     * <p>This implementation iterates over the specified map's

     * <tt>entrySet()</tt> collection, and calls this map's <tt>put</tt>

     * operation once for each entry returned by the iteration.

     *

     * <p>Note that this implementation throws an

     * <tt>UnsupportedOperationException</tt> if this map does not support

     * the <tt>put</tt> 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}

     *

     * <p>This implementation calls <tt>entrySet().clear()</tt>.

     *

     * <p>Note that this implementation throws an

     * <tt>UnsupportedOperationException</tt> if the <tt>entrySet</tt>

     * does not support the <tt>clear</tt> 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.

     */

    transient volatile Set<K>        keySet = null;

    transient volatile Collection<V> values = null;

    /**

     * {@inheritDoc}

     *

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

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

     * map's <tt>entrySet()</tt> iterator.  The <tt>size</tt> method

     * delegates to this map's <tt>size</tt> method and the

     * <tt>contains</tt> method delegates to this map's

     * <tt>containsKey</tt> 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() {

        if (keySet == null) {

            keySet = 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);

                }

            };

        }

        return keySet;

    }

    /**

     * {@inheritDoc}

     *

     * <p>This implementation returns a collection that subclasses {@link

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

     * "wrapper object" over this map's <tt>entrySet()</tt> iterator.

     * The <tt>size</tt> method delegates to this map's <tt>size</tt>

     * method and the <tt>contains</tt> method delegates to this map's

     * <tt>containsValue</tt> 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() {

        if (values == null) {

            values = 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);

                }

            };

        }

        return values;

    }

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

    // Comparison and hashing

    /**

     * Compares the specified object with this map for equality.  Returns

     * <tt>true</tt> if the given object is also a map and the two maps

     * represent the same mappings.  More formally, two maps <tt>m1</tt> and

     * <tt>m2</tt> represent the same mappings if

     * <tt>m1.entrySet().equals(m2.entrySet())</tt>.  This ensures that the

     * <tt>equals</tt> method works properly across different implementations

     * of the <tt>Map</tt> interface.

     *

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

     * if so it returns <tt>true</tt>.  Then, it checks if the specified

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

     * not, it returns <tt>false</tt>.  If so, it iterates over this map's

     * <tt>entrySet</tt> collection, and checks that the specified map

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

     * fails to contain such a mapping, <tt>false</tt> is returned.  If the

     * iteration completes, <tt>true</tt> is returned.

     *

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

     * @return <tt>true</tt> 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<K,V> m = (Map<K,V>) o;

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

            return false;

        try {

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

            while (i.hasNext()) {

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

                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

     * <tt>entrySet()</tt> view.  This ensures that <tt>m1.equals(m2)</tt>

     * implies that <tt>m1.hashCode()==m2.hashCode()</tt> for any two maps

     * <tt>m1</tt> and <tt>m2</tt>, as required by the general contract of

     * {@link Object#hashCode}.

     *

     * <p>This implementation iterates over <tt>entrySet()</tt>, calling

     * {@link Map.Entry#hashCode hashCode()} on each element (entry) in the

     * set, and adding up the results.

     *

     * @return the hash code value for this map

     * @see Map.Entry#hashCode()

     * @see Object#equals(Object)

     * @see Set#equals(Object)

     */

    public int hashCode() {

        int h = 0;

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

        while (i.hasNext())

            h += i.next().hashCode();

        return h;

    }

    /**

     * Returns a string representation of this map.  The string representation

     * consists of a list of key-value mappings in the order returned by the

     * map's <tt>entrySet</tt> view's iterator, enclosed in braces

     * (<tt>"{}"</tt>).  Adjacent mappings are separated by the characters

     * <tt>", "</tt> (comma and space).  Each key-value mapping is rendered as

     * the key followed by an equals sign (<tt>"="</tt>) followed by the

     * associated value.  Keys and values are converted to strings as by

     * {@link String#valueOf(Object)}.

     *

     * @return a string representation of this map

     */

    public String toString() {

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

        if (! i.hasNext())

            return "{}";

        StringBuilder sb = new StringBuilder();

        sb.append('{');

        for (;;) {

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

            K key = e.getKey();

            V value = e.getValue();

            sb.append(key   == this ? "(this Map)" : key);

            sb.append('=');

            sb.append(value == this ? "(this Map)" : value);

            if (! i.hasNext())

                return sb.append('}').toString();

            sb.append(',').append(' ');

        }