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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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package java.util;
import java.util.Map.Entry;

This class provides a skeletal implementation of the Map interface, to minimize the effort required to implement this interface. 
To implement an unmodifiable map, the programmer needs only to extend this class and provide an implementation for the entrySet method, which returns a set-view of the map's mappings. Typically, the returned set will, in turn, be implemented atop AbstractSet. This set should not support the add or remove methods, and its iterator should not support the remove method. 
To implement a modifiable map, the programmer must additionally override this class's put method (which otherwise throws an UnsupportedOperationException), and the iterator returned by entrySet().iterator() must additionally implement its remove method. 
The programmer should generally provide a void (no argument) and map constructor, as per the recommendation in the Map interface specification. 
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.
This class is a member of the

Java Collections Framework.
Author:
 Josh Bloch,  Neal Gafter
Type parameters:
<K> – the type of keys maintained by this map
<V> – the type of mapped values
See Also:
Map
Collection
Since:
1.2/**
 * 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.)
/**
     * Sole constructor.  (For invocation by subclass constructors, typically
     * implicit.)
     */
    protected AbstractMap() {
    }

    // Query Operations

    
{@inheritDoc}
Implementation Requirements:
 This implementation returns entrySet().size()./**
     * {@inheritDoc}
     *
     * @implSpec
     * This implementation returns {@code entrySet().size()}.
     */
    public int size() {
        return entrySet().size();
    }

    
{@inheritDoc}
Implementation Requirements:
 This implementation returns size() == 0./**
     * {@inheritDoc}
     *
     * @implSpec
     * This implementation returns {@code size() == 0}.
     */
    public boolean isEmpty() {
        return size() == 0;
    }

    
{@inheritDoc}
Throws:
ClassCastException –   {@inheritDoc}
NullPointerException – {@inheritDoc}
Implementation Requirements:
 This implementation iterates over entrySet() searching for an entry with the specified value. If such an entry is found, true is returned. If the iteration terminates without finding such an entry, false is returned. Note that this implementation requires linear time in the size of the map./**
     * {@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}
Throws:
ClassCastException –   {@inheritDoc}
NullPointerException – {@inheritDoc}
Implementation Requirements:
 This implementation iterates over entrySet() searching for an entry with the specified key. If such an entry is found, true is returned. If the iteration terminates without finding such an entry, false is returned. Note that this implementation requires linear time in the size of the map; many implementations will override this method./**
     * {@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}
Throws:
ClassCastException –            {@inheritDoc}
NullPointerException –          {@inheritDoc}
Implementation Requirements:
 This implementation iterates over 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, null is returned. Note that this implementation requires linear time in the size of the map; many implementations will override this method./**
     * {@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}
Throws:
UnsupportedOperationException – {@inheritDoc}
ClassCastException –            {@inheritDoc}
NullPointerException –          {@inheritDoc}
IllegalArgumentException –      {@inheritDoc}
Implementation Requirements:
 This implementation always throws an UnsupportedOperationException./**
     * {@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}
Throws:
UnsupportedOperationException – {@inheritDoc}
ClassCastException –            {@inheritDoc}
NullPointerException –          {@inheritDoc}
Implementation Requirements:
 This implementation iterates over entrySet() searching for an entry with the specified key. If such an entry is found, its value is obtained with its getValue operation, the entry is removed from the collection (and the backing map) with the iterator's remove operation, and the saved value is returned. If the iteration terminates without finding such an entry, null is returned. Note that this implementation requires linear time in the size of the map; many implementations will override this method. 
Note that this implementation throws an UnsupportedOperationException if the entrySet iterator does not support the remove method and this map contains a mapping for the specified key./**
     * {@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}
Throws:
UnsupportedOperationException – {@inheritDoc}
ClassCastException –            {@inheritDoc}
NullPointerException –          {@inheritDoc}
IllegalArgumentException –      {@inheritDoc}
Implementation Requirements:
 This implementation iterates over the specified map's entrySet() collection, and calls this map's put operation once for each entry returned by the iteration. 
Note that this implementation throws an UnsupportedOperationException if this map does not support the put operation and the specified map is nonempty./**
     * {@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}
Throws:
UnsupportedOperationException – {@inheritDoc}
Implementation Requirements:
 This implementation calls entrySet().clear(). 
Note that this implementation throws an UnsupportedOperationException if the entrySet does not support the clear operation./**
     * {@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.
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.
It is also imperative that implementations read the field only once,
as in:
 
public Set<K> keySet() {
  Set<K> ks = keySet;  // single racy read
  if (ks == null) {
    ks = new KeySet();
    keySet = ks;
  }
  return ks;
 }

/**
     * 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}
Implementation Requirements:
 This implementation returns a set that subclasses AbstractSet. The subclass's iterator method returns a "wrapper object" over this map's entrySet() iterator. The size method delegates to this map's size method and the contains method delegates to this map's containsKey method. 
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./**
     * {@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}
Implementation Requirements:
 This implementation returns a collection that subclasses AbstractCollection. The subclass's iterator method returns a "wrapper object" over this map's entrySet() iterator. The size method delegates to this map's size method and the contains method delegates to this map's containsValue method. 
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./**
     * {@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 true if the given object is also a map and the two maps represent the same mappings. More formally, two maps m1 and m2 represent the same mappings if m1.entrySet().equals(m2.entrySet()). This ensures that the equals method works properly across different implementations of the Map interface. 
Params:
o – object to be compared for equality with this map
Implementation Requirements:
 This implementation first checks if the specified object is this map; if so it returns 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 false. If so, it iterates over this map's 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, false is returned. If the iteration completes, true is returned.
Returns:
true if the specified object is equal to this map/**
     * 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 entrySet() view. This ensures that m1.equals(m2) implies that m1.hashCode()==m2.hashCode() for any two maps m1 and m2, as required by the general contract of Object.hashCode. 
See Also:
Entry.hashCode()
Object.equals(Object)
Set.equals(Object)
Implementation Requirements:
 This implementation iterates over entrySet(), calling hashCode() on each element (entry) in the set, and adding up the results.
Returns:
the hash code value for this map/**
     * 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
     * This implementation iterates over {@code entrySet()}, 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;
        for (Entry<K, V> entry : entrySet())
            h += entry.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 entrySet view's iterator, enclosed in braces ("{}"). Adjacent mappings are separated by the characters ", " (comma and space). Each key-value mapping is rendered as the key followed by an equals sign ("=") followed by the associated value. Keys and values are converted to strings as by String.valueOf(Object). 
Returns:
a string representation of this map/**
     * 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 {@code entrySet} view's iterator, enclosed in braces
     * ({@code "{}"}).  Adjacent mappings are separated by the characters
     * {@code ", "} (comma and space).  Each key-value mapping is rendered as
     * the key followed by an equals sign ({@code "="}) 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 AbstractMap instance: the keys and values themselves are not cloned. 
Returns:
a shallow copy of this map/**
     * Returns a shallow copy of this {@code AbstractMap} instance: the keys
     * and values themselves are not cloned.
     *
     * @return a shallow copy of this map
     */
    protected Object clone() throws CloneNotSupportedException {
        AbstractMap<?,?> result = (AbstractMap<?,?>)super.clone();
        result.keySet = null;
        result.values = null;
        return result;
    }

    
Utility method for SimpleEntry and SimpleImmutableEntry.
Test for equality, checking for nulls.
NB: Do not replace with Object.equals until JDK-8015417 is resolved.
/**
     * Utility method for SimpleEntry and SimpleImmutableEntry.
     * Test for equality, checking for nulls.
     *
     * NB: Do not replace with Object.equals until JDK-8015417 is resolved.
     */
    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 setValue method. This class facilitates the process of building custom map implementations. For example, it may be convenient to return arrays of SimpleEntry instances in method Map.entrySet().toArray. 
Since:
1.6/**
     * An Entry maintaining a key and a value.  The value may be
     * changed using the {@code setValue} method.  This class
     * facilitates the process of building custom map
     * implementations. For example, it may be convenient to return
     * arrays of {@code SimpleEntry} instances in method
     * {@code Map.entrySet().toArray}.
     *
     * @since 1.6
     */
    public static class SimpleEntry<K,V>
        implements Entry<K,V>, java.io.Serializable
    {
        @java.io.Serial
        private static final long serialVersionUID = -8499721149061103585L;

        @SuppressWarnings("serial") // Conditionally serializable
        private final K key;
        @SuppressWarnings("serial") // Conditionally serializable
        private V value;

        
Creates an entry representing a mapping from the specified
key to the specified value.
Params:
key – the key represented by this entry
value – the value represented by this entry/**
         * 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.
Params:
entry – the entry to copy/**
         * 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.
Returns:
the key corresponding to this entry/**
         * 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.
Returns:
the value corresponding to this entry/**
         * 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.
Params:
value – new value to be stored in this entry
Returns:
the old value corresponding to the entry/**
         * 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 true if the given object is also a map entry and the two entries represent the same mapping. More formally, two entries e1 and e2 represent the same mapping if
  (e1.getKey()==null ?
   e2.getKey()==null :
   e1.getKey().equals(e2.getKey()))
  &&
  (e1.getValue()==null ?
   e2.getValue()==null :
   e1.getValue().equals(e2.getValue()))
 This ensures that the equals method works properly across different implementations of the Map.Entry interface. 
Params:
o – object to be compared for equality with this map entry
See Also:
hashCode
Returns:
true if the specified object is equal to this map entry/**
         * 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()))
         *   &amp;&amp;
         *   (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 e is defined to be: 
  (e.getKey()==null   ? 0 : e.getKey().hashCode()) ^
  (e.getValue()==null ? 0 : e.getValue().hashCode())
 This ensures that e1.equals(e2) implies that e1.hashCode()==e2.hashCode() for any two Entries e1 and e2, as required by the general contract of Object.hashCode. 
See Also:
equals
Returns:
the hash code value for this map entry/**
         * 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 ("=") followed by the string representation of this entry's value. 
Returns:
a String representation of this map entry/**
         * Returns a String representation of this map entry.  This
         * implementation returns the string representation of this
         * entry's key followed by the equals character ("{@code =}")
         * 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 setValue. This class may be convenient in methods that return thread-safe snapshots of key-value mappings. 
Since:
1.6/**
     * An Entry maintaining an immutable key and value.  This class
     * does not support method {@code setValue}.  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
    {
        @java.io.Serial
        private static final long serialVersionUID = 7138329143949025153L;

        @SuppressWarnings("serial") // Not statically typed as Serializable
        private final K key;
        @SuppressWarnings("serial") // Not statically typed as Serializable
        private final V value;

        
Creates an entry representing a mapping from the specified
key to the specified value.
Params:
key – the key represented by this entry
value – the value represented by this entry/**
         * 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.
Params:
entry – the entry to copy/**
         * 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.
Returns:
the key corresponding to this entry/**
         * 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.
Returns:
the value corresponding to this entry/**
         * 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 UnsupportedOperationException, as this class implements an immutable map entry.
Params:
value – new value to be stored in this entry
Throws:
UnsupportedOperationException – always
Returns:
(Does not return)/**
         * Replaces the value corresponding to this entry with the specified
         * value (optional operation).  This implementation simply throws
         * {@code UnsupportedOperationException}, 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 true if the given object is also a map entry and the two entries represent the same mapping. More formally, two entries e1 and e2 represent the same mapping if
  (e1.getKey()==null ?
   e2.getKey()==null :
   e1.getKey().equals(e2.getKey()))
  &&
  (e1.getValue()==null ?
   e2.getValue()==null :
   e1.getValue().equals(e2.getValue()))
 This ensures that the equals method works properly across different implementations of the Map.Entry interface. 
Params:
o – object to be compared for equality with this map entry
See Also:
hashCode
Returns:
true if the specified object is equal to this map entry/**
         * 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()))
         *   &amp;&amp;
         *   (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 e is defined to be: 
  (e.getKey()==null   ? 0 : e.getKey().hashCode()) ^
  (e.getValue()==null ? 0 : e.getValue().hashCode())
 This ensures that e1.equals(e2) implies that e1.hashCode()==e2.hashCode() for any two Entries e1 and e2, as required by the general contract of Object.hashCode. 
See Also:
equals
Returns:
the hash code value for this map entry/**
         * 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 ("=") followed by the string representation of this entry's value. 
Returns:
a String representation of this map entry/**
         * Returns a String representation of this map entry.  This
         * implementation returns the string representation of this
         * entry's key followed by the equals character ("{@code =}")
         * followed by the string representation of this entry's value.
         *
         * @return a String representation of this map entry
         */
        public String toString() {
            return key + "=" + value;
        }

    }

}