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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(' ');

         }

     }

     /**

      * Returns a shallow copy of this <tt>AbstractMap</tt> instance: the keys

      * and values themselves are not cloned.

      *

      * @return a shallow copy of this map

      */

     protected Object clone() throws CloneNotSupportedException {

         AbstractMap<K,V> result = (AbstractMap<K,V>)super.clone();

         result.keySet = null;

         result.values = null;

         return result;

     }

     /**

      * Utility method for SimpleEntry and SimpleImmutableEntry.

      * Test for equality, checking for nulls.

      */

     private static boolean eq(Object o1, Object o2) {

         return o1 == null ? o2 == null : o1.equals(o2);

     }

     // Implementation Note: SimpleEntry and SimpleImmutableEntry

     // are distinct unrelated classes, even though they share

     // some code. Since you can't add or subtract final-ness

     // of a field in a subclass, they can't share representations,

     // and the amount of duplicated code is too small to warrant

     // exposing a common abstract class.

     /**

      * An Entry maintaining a key and a value.  The value may be

      * changed using the <tt>setValue</tt> method.  This class

      * facilitates the process of building custom map

      * implementations. For example, it may be convenient to return

      * arrays of <tt>SimpleEntry</tt> instances in method

      * <tt>Map.entrySet().toArray</tt>.

      *

      * @since 1.6

      */

     public static class SimpleEntry<K,V>

         implements Entry<K,V>, java.io.Serializable

     {

         private static final long serialVersionUID = -8499721149061103585L;

         private final K key;

         private V value;

         /**

          * Creates an entry representing a mapping from the specified

          * key to the specified value.

          *

          * @param key the key represented by this entry

          * @param value the value represented by this entry

          */

         public SimpleEntry(K key, V value) {

             this.key   = key;

             this.value = value;

         }

         /**

          * Creates an entry representing the same mapping as the

          * specified entry.

          *

          * @param entry the entry to copy

          */

         public SimpleEntry(Entry<? extends K, ? extends V> entry) {

             this.key   = entry.getKey();

             this.value = entry.getValue();

         }

         /**

          * Returns the key corresponding to this entry.

          *

          * @return the key corresponding to this entry

          */

         public K getKey() {

             return key;

         }

         /**

          * Returns the value corresponding to this entry.

          *

          * @return the value corresponding to this entry

          */

         public V getValue() {

             return value;

         }

         /**

          * Replaces the value corresponding to this entry with the specified

          * value.

          *

          * @param value new value to be stored in this entry

          * @return the old value corresponding to the entry

          */

         public V setValue(V value) {

             V oldValue = this.value;

             this.value = value;

             return oldValue;

         }

         /**

          * Compares the specified object with this entry for equality.

          * Returns {@code true} if the given object is also a map entry and

          * the two entries represent the same mapping.  More formally, two

          * entries {@code e1} and {@code e2} represent the same mapping

          * if<pre>

          *   (e1.getKey()==null ?

          *    e2.getKey()==null :

          *    e1.getKey().equals(e2.getKey()))

          *   &&

          *   (e1.getValue()==null ?

          *    e2.getValue()==null :

          *    e1.getValue().equals(e2.getValue()))</pre>

          * This ensures that the {@code equals} method works properly across

          * different implementations of the {@code Map.Entry} interface.

          *

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

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

          *         entry

          * @see    #hashCode

          */

         public boolean equals(Object o) {

             if (!(o instanceof Map.Entry))

                 return false;

             Map.Entry e = (Map.Entry)o;

             return eq(key, e.getKey()) && eq(value, e.getValue());

         }

         /**

          * Returns the hash code value for this map entry.  The hash code

          * of a map entry {@code e} is defined to be: <pre>

          *   (e.getKey()==null   ? 0 : e.getKey().hashCode()) ^

          *   (e.getValue()==null ? 0 : e.getValue().hashCode())</pre>

          * This ensures that {@code e1.equals(e2)} implies that

          * {@code e1.hashCode()==e2.hashCode()} for any two Entries

          * {@code e1} and {@code e2}, as required by the general

          * contract of {@link Object#hashCode}.

          *

          * @return the hash code value for this map entry

          * @see    #equals

          */

         public int hashCode() {

             return (key   == null ? 0 :   key.hashCode()) ^

                    (value == null ? 0 : value.hashCode());

         }

         /**

          * Returns a String representation of this map entry.  This

          * implementation returns the string representation of this

          * entry's key followed by the equals character ("<tt>=</tt>")

          * followed by the string representation of this entry's value.

          *

          * @return a String representation of this map entry

          */

         public String toString() {

             return key + "=" + value;

         }

     }

     /**

      * An Entry maintaining an immutable key and value.  This class

      * does not support method <tt>setValue</tt>.  This class may be

      * convenient in methods that return thread-safe snapshots of

      * key-value mappings.

      *

      * @since 1.6

      */

     public static class SimpleImmutableEntry<K,V>

         implements Entry<K,V>, java.io.Serializable

     {

         private static final long serialVersionUID = 7138329143949025153L;

         private final K key;

         private final V value;

         /**

          * Creates an entry representing a mapping from the specified

          * key to the specified value.

          *

          * @param key the key represented by this entry

          * @param value the value represented by this entry

          */

         public SimpleImmutableEntry(K key, V value) {

             this.key   = key;

             this.value = value;

         }

         /**

          * Creates an entry representing the same mapping as the

          * specified entry.

          *

          * @param entry the entry to copy

          */

         public SimpleImmutableEntry(Entry<? extends K, ? extends V> entry) {

             this.key   = entry.getKey();

             this.value = entry.getValue();

         }

         /**

          * Returns the key corresponding to this entry.

          *

          * @return the key corresponding to this entry

          */

         public K getKey() {

             return key;

         }

         /**

          * Returns the value corresponding to this entry.

          *

          * @return the value corresponding to this entry

          */

         public V getValue() {

             return value;

         }

         /**

          * Replaces the value corresponding to this entry with the specified

          * value (optional operation).  This implementation simply throws

          * <tt>UnsupportedOperationException</tt>, as this class implements

          * an <i>immutable</i> map entry.

          *

          * @param value new value to be stored in this entry

          * @return (Does not return)

          * @throws UnsupportedOperationException always

          */

         public V setValue(V value) {

             throw new UnsupportedOperationException();

         }

         /**

          * Compares the specified object with this entry for equality.

          * Returns {@code true} if the given object is also a map entry and

          * the two entries represent the same mapping.  More formally, two

          * entries {@code e1} and {@code e2} represent the same mapping

          * if<pre>

          *   (e1.getKey()==null ?

          *    e2.getKey()==null :

          *    e1.getKey().equals(e2.getKey()))

          *   &&

          *   (e1.getValue()==null ?

          *    e2.getValue()==null :

          *    e1.getValue().equals(e2.getValue()))</pre>

          * This ensures that the {@code equals} method works properly across

          * different implementations of the {@code Map.Entry} interface.

          *

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

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

          *         entry

          * @see    #hashCode

          */

         public boolean equals(Object o) {

             if (!(o instanceof Map.Entry))

                 return false;

             Map.Entry e = (Map.Entry)o;

             return eq(key, e.getKey()) && eq(value, e.getValue());

         }

         /**

          * Returns the hash code value for this map entry.  The hash code

          * of a map entry {@code e} is defined to be: <pre>

          *   (e.getKey()==null   ? 0 : e.getKey().hashCode()) ^

          *   (e.getValue()==null ? 0 : e.getValue().hashCode())</pre>

          * This ensures that {@code e1.equals(e2)} implies that

          * {@code e1.hashCode()==e2.hashCode()} for any two Entries

          * {@code e1} and {@code e2}, as required by the general

          * contract of {@link Object#hashCode}.

          *

          * @return the hash code value for this map entry

          * @see    #equals

          */

         public int hashCode() {

             return (key   == null ? 0 :   key.hashCode()) ^

                    (value == null ? 0 : value.hashCode());

         }

         /**

          * Returns a String representation of this map entry.  This

          * implementation returns the string representation of this

          * entry's key followed by the equals character ("<tt>=</tt>")

          * followed by the string representation of this entry's value.

          *

          * @return a String representation of this map entry

          */

         public String toString() {

             return key + "=" + value;

         }

     }

 }