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 * Copyright (c) 1997, 2018, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package java.util;
import java.util.Map.Entry;

/**
 * This class provides a skeletal implementation of the {@code Map}
 * interface, to minimize the effort required to implement this interface.
 *
 * <p>To implement an unmodifiable map, the programmer needs only to extend this
 * class and provide an implementation for the {@code entrySet} method, which
 * returns a set-view of the map's mappings. Typically, the returned set
 * will, in turn, be implemented atop {@code AbstractSet}. This set should
 * not support the {@code add} or {@code remove} methods, and its iterator
 * should not support the {@code remove} method.
 *
 * <p>To implement a modifiable map, the programmer must additionally override
 * this class's {@code put} method (which otherwise throws an
 * {@code UnsupportedOperationException}), and the iterator returned by
 * {@code entrySet().iterator()} must additionally implement its
 * {@code remove} method.
 *
 * <p>The programmer should generally provide a void (no argument) and map
 * constructor, as per the recommendation in the {@code Map} interface
 * specification.
 *
 * <p>The documentation for each non-abstract method in this class describes its
 * implementation in detail. Each of these methods may be overridden if the
 * map being implemented admits a more efficient implementation.
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
 * Java Collections Framework</a>.
 *
 * @param <K> the type of keys maintained by this map
 * @param <V> the type of mapped values
 *
 * @author Josh Bloch
 * @author Neal Gafter
 * @see Map
 * @see Collection
 * @since 1.2
 */

public abstract class AbstractMap<K,V> implements Map<K,V> {
 /**
 * Sole constructor. (For invocation by subclass constructors, typically
 * implicit.)
 */
 protected AbstractMap() {
 }

 // Query Operations

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

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

 /**
 * {@inheritDoc}
 *
 * @implSpec
 * This implementation iterates over {@code entrySet()} searching
 * for an entry with the specified value. If such an entry is found,
 * {@code true} is returned. If the iteration terminates without
 * finding such an entry, {@code false} is returned. Note that this
 * implementation requires linear time in the size of the map.
 *
 * @throws ClassCastException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 */
 public boolean containsValue(Object value) {
 Iterator<Entry<K,V>> i = entrySet().iterator();
 if (value==null) {
 while (i.hasNext()) {
 Entry<K,V> e = i.next();
 if (e.getValue()==null)
 return true;
 }
 } else {
 while (i.hasNext()) {
 Entry<K,V> e = i.next();
 if (value.equals(e.getValue()))
 return true;
 }
 }
 return false;
 }

 /**
 * {@inheritDoc}
 *
 * @implSpec
 * This implementation iterates over {@code entrySet()} searching
 * for an entry with the specified key. If such an entry is found,
 * {@code true} is returned. If the iteration terminates without
 * finding such an entry, {@code false} is returned. Note that this
 * implementation requires linear time in the size of the map; many
 * implementations will override this method.
 *
 * @throws ClassCastException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 */
 public boolean containsKey(Object key) {
 Iterator<Map.Entry<K,V>> i = entrySet().iterator();
 if (key==null) {
 while (i.hasNext()) {
 Entry<K,V> e = i.next();
 if (e.getKey()==null)
 return true;
 }
 } else {
 while (i.hasNext()) {
 Entry<K,V> e = i.next();
 if (key.equals(e.getKey()))
 return true;
 }
 }
 return false;
 }

 /**
 * {@inheritDoc}
 *
 * @implSpec
 * This implementation iterates over {@code entrySet()} searching
 * for an entry with the specified key. If such an entry is found,
 * the entry's value is returned. If the iteration terminates without
 * finding such an entry, {@code null} is returned. Note that this
 * implementation requires linear time in the size of the map; many
 * implementations will override this method.
 *
 * @throws ClassCastException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 */
 public V get(Object key) {
 Iterator<Entry<K,V>> i = entrySet().iterator();
 if (key==null) {
 while (i.hasNext()) {
 Entry<K,V> e = i.next();
 if (e.getKey()==null)
 return e.getValue();
 }
 } else {
 while (i.hasNext()) {
 Entry<K,V> e = i.next();
 if (key.equals(e.getKey()))
 return e.getValue();
 }
 }
 return null;
 }


 // Modification Operations

 /**
 * {@inheritDoc}
 *
 * @implSpec
 * This implementation always throws an
 * {@code UnsupportedOperationException}.
 *
 * @throws UnsupportedOperationException {@inheritDoc}
 * @throws ClassCastException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 * @throws IllegalArgumentException {@inheritDoc}
 */
 public V put(K key, V value) {
 throw new UnsupportedOperationException();
 }

 /**
 * {@inheritDoc}
 *
 * @implSpec
 * This implementation iterates over {@code entrySet()} searching for an
 * entry with the specified key. If such an entry is found, its value is
 * obtained with its {@code getValue} operation, the entry is removed
 * from the collection (and the backing map) with the iterator's
 * {@code remove} operation, and the saved value is returned. If the
 * iteration terminates without finding such an entry, {@code null} is
 * returned. Note that this implementation requires linear time in the
 * size of the map; many implementations will override this method.
 *
 * <p>Note that this implementation throws an
 * {@code UnsupportedOperationException} if the {@code entrySet}
 * iterator does not support the {@code remove} method and this map
 * contains a mapping for the specified key.
 *
 * @throws UnsupportedOperationException {@inheritDoc}
 * @throws ClassCastException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 */
 public V remove(Object key) {
 Iterator<Entry<K,V>> i = entrySet().iterator();
 Entry<K,V> correctEntry = null;
 if (key==null) {
 while (correctEntry==null && i.hasNext()) {
 Entry<K,V> e = i.next();
 if (e.getKey()==null)
 correctEntry = e;
 }
 } else {
 while (correctEntry==null && i.hasNext()) {
 Entry<K,V> e = i.next();
 if (key.equals(e.getKey()))
 correctEntry = e;
 }
 }

 V oldValue = null;
 if (correctEntry !=null) {
 oldValue = correctEntry.getValue();
 i.remove();
 }
 return oldValue;
 }


 // Bulk Operations

 /**
 * {@inheritDoc}
 *
 * @implSpec
 * This implementation iterates over the specified map's
 * {@code entrySet()} collection, and calls this map's {@code put}
 * operation once for each entry returned by the iteration.
 *
 * <p>Note that this implementation throws an
 * {@code UnsupportedOperationException} if this map does not support
 * the {@code put} operation and the specified map is nonempty.
 *
 * @throws UnsupportedOperationException {@inheritDoc}
 * @throws ClassCastException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 * @throws IllegalArgumentException {@inheritDoc}
 */
 public void putAll(Map<? extends K, ? extends V> m) {
 for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
 put(e.getKey(), e.getValue());
 }

 /**
 * {@inheritDoc}
 *
 * @implSpec
 * This implementation calls {@code entrySet().clear()}.
 *
 * <p>Note that this implementation throws an
 * {@code UnsupportedOperationException} if the {@code entrySet}
 * does not support the {@code clear} operation.
 *
 * @throws UnsupportedOperationException {@inheritDoc}
 */
 public void clear() {
 entrySet().clear();
 }


 // Views

 /**
 * Each of these fields are initialized to contain an instance of the
 * appropriate view the first time this view is requested. The views are
 * stateless, so there's no reason to create more than one of each.
 *
 * <p>Since there is no synchronization performed while accessing these fields,
 * it is expected that java.util.Map view classes using these fields have
 * no non-final fields (or any fields at all except for outer-this). Adhering
 * to this rule would make the races on these fields benign.
 *
 * <p>It is also imperative that implementations read the field only once,
 * as in:
 *
 * <pre> {@code
 * public Set<K> keySet() {
 * Set<K> ks = keySet; // single racy read
 * if (ks == null) {
 * ks = new KeySet();
 * keySet = ks;
 * }
 * return ks;
 * }
 *}</pre>
 */
 transient Set<K> keySet;
 transient Collection<V> values;

 /**
 * {@inheritDoc}
 *
 * @implSpec
 * This implementation returns a set that subclasses {@link AbstractSet}.
 * The subclass's iterator method returns a "wrapper object" over this
 * map's {@code entrySet()} iterator. The {@code size} method
 * delegates to this map's {@code size} method and the
 * {@code contains} method delegates to this map's
 * {@code containsKey} method.
 *
 * <p>The set is created the first time this method is called,
 * and returned in response to all subsequent calls. No synchronization
 * is performed, so there is a slight chance that multiple calls to this
 * method will not all return the same set.
 */
 public Set<K> keySet() {
 Set<K> ks = keySet;
 if (ks == null) {
 ks = new AbstractSet<K>() {
 public Iterator<K> iterator() {
 return new Iterator<K>() {
 private Iterator<Entry<K,V>> i = entrySet().iterator();

 public boolean hasNext() {
 return i.hasNext();
 }

 public K next() {
 return i.next().getKey();
 }

 public void remove() {
 i.remove();
 }
 };
 }

 public int size() {
 return AbstractMap.this.size();
 }

 public boolean isEmpty() {
 return AbstractMap.this.isEmpty();
 }

 public void clear() {
 AbstractMap.this.clear();
 }

 public boolean contains(Object k) {
 return AbstractMap.this.containsKey(k);
 }
 };
 keySet = ks;
 }
 return ks;
 }

 /**
 * {@inheritDoc}
 *
 * @implSpec
 * This implementation returns a collection that subclasses {@link
 * AbstractCollection}. The subclass's iterator method returns a
 * "wrapper object" over this map's {@code entrySet()} iterator.
 * The {@code size} method delegates to this map's {@code size}
 * method and the {@code contains} method delegates to this map's
 * {@code containsValue} method.
 *
 * <p>The collection is created the first time this method is called, and
 * returned in response to all subsequent calls. No synchronization is
 * performed, so there is a slight chance that multiple calls to this
 * method will not all return the same collection.
 */
 public Collection<V> values() {
 Collection<V> vals = values;
 if (vals == null) {
 vals = new AbstractCollection<V>() {
 public Iterator<V> iterator() {
 return new Iterator<V>() {
 private Iterator<Entry<K,V>> i = entrySet().iterator();

 public boolean hasNext() {
 return i.hasNext();
 }

 public V next() {
 return i.next().getValue();
 }

 public void remove() {
 i.remove();
 }
 };
 }

 public int size() {
 return AbstractMap.this.size();
 }

 public boolean isEmpty() {
 return AbstractMap.this.isEmpty();
 }

 public void clear() {
 AbstractMap.this.clear();
 }

 public boolean contains(Object v) {
 return AbstractMap.this.containsValue(v);
 }
 };
 values = vals;
 }
 return vals;
 }

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


 // Comparison and hashing

 /**
 * Compares the specified object with this map for equality. Returns
 * {@code true} if the given object is also a map and the two maps
 * represent the same mappings. More formally, two maps {@code m1} and
 * {@code m2} represent the same mappings if
 * {@code m1.entrySet().equals(m2.entrySet())}. This ensures that the
 * {@code equals} method works properly across different implementations
 * of the {@code Map} interface.
 *
 * @implSpec
 * This implementation first checks if the specified object is this map;
 * if so it returns {@code true}. Then, it checks if the specified
 * object is a map whose size is identical to the size of this map; if
 * not, it returns {@code false}. If so, it iterates over this map's
 * {@code entrySet} collection, and checks that the specified map
 * contains each mapping that this map contains. If the specified map
 * fails to contain such a mapping, {@code false} is returned. If the
 * iteration completes, {@code true} is returned.
 *
 * @param o object to be compared for equality with this map
 * @return {@code true} if the specified object is equal to this map
 */
 public boolean equals(Object o) {
 if (o == this)
 return true;

 if (!(o instanceof Map))
 return false;
 Map<?,?> m = (Map<?,?>) o;
 if (m.size() != size())
 return false;

 try {
 for (Entry<K, V> e : entrySet()) {
 K key = e.getKey();
 V value = e.getValue();
 if (value == null) {
 if (!(m.get(key) == null && m.containsKey(key)))
 return false;
 } else {
 if (!value.equals(m.get(key)))
 return false;
 }
 }
 } catch (ClassCastException unused) {
 return false;
 } catch (NullPointerException unused) {
 return false;
 }

 return true;
 }

 /**
 * Returns the hash code value for this map. The hash code of a map is
 * defined to be the sum of the hash codes of each entry in the map's
 * {@code entrySet()} view. This ensures that {@code m1.equals(m2)}
 * implies that {@code m1.hashCode()==m2.hashCode()} for any two maps
 * {@code m1} and {@code m2}, as required by the general contract of
 * {@link Object#hashCode}.
 *
 * @implSpec
 * 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 {@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 {@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.
 */
 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 {@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
 {
 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()))
 * &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 {@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 ("{@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 {@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
 {
 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
 * {@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 {@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 {@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 ("{@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;
 }

 }

}