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## org.apache.commons.collections.map
Class AbstractHashedMap

    java.lang.Object
      java.util.AbstractMap
          org.apache.commons.collections.map.AbstractHashedMap

All Implemented Interfaces:
  java.util.Map, IterableMap

Direct Known Subclasses:
  AbstractLinkedMap, AbstractReferenceMap, CaseInsensitiveMap, HashedMap, IdentityMap

    public class AbstractHashedMap

extends java.util.AbstractMap
implements IterableMap

An abstract implementation of a hash-based map which provides numerous points for subclasses to override.

This class implements all the features necessary for a subclass hash-based map. Key-value entries are stored in instances of the `HashEntry` class, which can be overridden and replaced. The iterators can similarly be replaced, without the need to replace the KeySet, EntrySet and Values view classes.

Overridable methods are provided to change the default hashing behaviour, and to change how entries are added to and removed from the map. Hopefully, all you need for unusual subclasses is here.

NOTE: From Commons Collections 3.1 this class extends AbstractMap. This is to provide backwards compatibility for ReferenceMap between v3.0 and v3.1. This extends clause will be removed in v4.0.

Since:
  Commons Collections 3.0
Version:
  $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
Author:
  java util HashMap, Stephen Colebourne, Christian Siefkes

Nested Class Summary
`protected static class` | `AbstractHashedMap.EntrySet` EntrySet implementation.
`protected static class` | `AbstractHashedMap.EntrySetIterator` EntrySet iterator.
`protected static class` | `AbstractHashedMap.HashEntry` HashEntry used to store the data.
`protected static class` | `AbstractHashedMap.HashIterator` Base Iterator
`protected static class` | `AbstractHashedMap.HashMapIterator` MapIterator implementation.
`protected static class` | `AbstractHashedMap.KeySet` KeySet implementation.
`protected static class` | `AbstractHashedMap.KeySetIterator` KeySet iterator.
`protected static class` | `AbstractHashedMap.Values` Values implementation.
`protected static class` | `AbstractHashedMap.ValuesIterator` Values iterator.

Nested classes/interfaces inherited from interface java.util.Map
`java.util.Map.Entry`

Field Summary
`protected AbstractHashedMap.HashEntry[]` | `data` Map entries
`protected static int` | `DEFAULT_CAPACITY` The default capacity to use
`protected static float` | `DEFAULT_LOAD_FACTOR` The default load factor to use
`protected static int` | `DEFAULT_THRESHOLD` The default threshold to use
`protected AbstractHashedMap.EntrySet` | `entrySet` Entry set
`protected static java.lang.String` | `GETKEY_INVALID`
`protected static java.lang.String` | `GETVALUE_INVALID`
`protected AbstractHashedMap.KeySet` | `keySet` Key set
`protected float` | `loadFactor` Load factor, normally 0.75
`protected static int` | `MAXIMUM_CAPACITY` The maximum capacity allowed
`protected int` | `modCount` Modification count for iterators
`protected static java.lang.String` | `NO_NEXT_ENTRY`
`protected static java.lang.String` | `NO_PREVIOUS_ENTRY`
`protected static java.lang.Object` | `NULL` An object for masking null
`protected static java.lang.String` | `REMOVE_INVALID`
`protected static java.lang.String` | `SETVALUE_INVALID`
`protected int` | `size` The size of the map
`protected int` | `threshold` Size at which to rehash
`protected AbstractHashedMap.Values` | `values` Values

Constructor Summary
`protected` | `AbstractHashedMap()` Constructor only used in deserialization, do not use otherwise.
`protected` | `AbstractHashedMap(int initialCapacity)` Constructs a new, empty map with the specified initial capacity and default load factor.
`protected` | `AbstractHashedMap(int initialCapacity, float loadFactor)` Constructs a new, empty map with the specified initial capacity and load factor.
`protected` | `AbstractHashedMap(int initialCapacity, float loadFactor, int threshold)` Constructor which performs no validation on the passed in parameters.
`protected` | `AbstractHashedMap(java.util.Map map)` Constructor copying elements from another map.

Method Summary
`protected void` | `addEntry(AbstractHashedMap.HashEntry entry, int hashIndex)` Adds an entry into this map.
`protected void` | `addMapping(int hashIndex, int hashCode, java.lang.Object key, java.lang.Object value)` Adds a new key-value mapping into this map.
`protected int` | `calculateNewCapacity(int proposedCapacity)` Calculates the new capacity of the map.
`protected int` | `calculateThreshold(int newCapacity, float factor)` Calculates the new threshold of the map, where it will be resized.
`protected void` | `checkCapacity()` Checks the capacity of the map and enlarges it if necessary.
`void` | `clear()` Clears the map, resetting the size to zero and nullifying references to avoid garbage collection issues.
`protected java.lang.Object` | `clone()` Clones the map without cloning the keys or values.
`boolean` | `containsKey(java.lang.Object key)` Checks whether the map contains the specified key.
`boolean` | `containsValue(java.lang.Object value)` Checks whether the map contains the specified value.
`protected java.lang.Object` | `convertKey(java.lang.Object key)` Converts input keys to another object for storage in the map.
`protected AbstractHashedMap.HashEntry` | `createEntry(AbstractHashedMap.HashEntry next, int hashCode, java.lang.Object key, java.lang.Object value)` Creates an entry to store the key-value data.
`protected java.util.Iterator` | `createEntrySetIterator()` Creates an entry set iterator.
`protected java.util.Iterator` | `createKeySetIterator()` Creates a key set iterator.
`protected java.util.Iterator` | `createValuesIterator()` Creates a values iterator.
`protected void` | `destroyEntry(AbstractHashedMap.HashEntry entry)` Kills an entry ready for the garbage collector.
`protected void` | `doReadObject(java.io.ObjectInputStream in)` Reads the map data from the stream.
`protected void` | `doWriteObject(java.io.ObjectOutputStream out)` Writes the map data to the stream.
`protected void` | `ensureCapacity(int newCapacity)` Changes the size of the data structure to the capacity proposed.
`protected int` | `entryHashCode(AbstractHashedMap.HashEntry entry)` Gets the `hashCode` field from a `HashEntry`.
`protected java.lang.Object` | `entryKey(AbstractHashedMap.HashEntry entry)` Gets the `key` field from a `HashEntry`.
`protected AbstractHashedMap.HashEntry` | `entryNext(AbstractHashedMap.HashEntry entry)` Gets the `next` field from a `HashEntry`.
`java.util.Set` | `entrySet()` Gets the entrySet view of the map.
`protected java.lang.Object` | `entryValue(AbstractHashedMap.HashEntry entry)` Gets the `value` field from a `HashEntry`.
`boolean` | `equals(java.lang.Object obj)` Compares this map with another.
`java.lang.Object` | `get(java.lang.Object key)` Gets the value mapped to the key specified.
`protected AbstractHashedMap.HashEntry` | `getEntry(java.lang.Object key)` Gets the entry mapped to the key specified.
`protected int` | `hash(java.lang.Object key)` Gets the hash code for the key specified.
`int` | `hashCode()` Gets the standard Map hashCode.
`protected int` | `hashIndex(int hashCode, int dataSize)` Gets the index into the data storage for the hashCode specified.
`protected void` | `init()` Initialise subclasses during construction, cloning or deserialization.
`boolean` | `isEmpty()` Checks whether the map is currently empty.
`protected boolean` | `isEqualKey(java.lang.Object key1, java.lang.Object key2)` Compares two keys, in internal converted form, to see if they are equal.
`protected boolean` | `isEqualValue(java.lang.Object value1, java.lang.Object value2)` Compares two values, in external form, to see if they are equal.
`java.util.Set` | `keySet()` Gets the keySet view of the map.
`MapIterator` | `mapIterator()` Gets an iterator over the map.
`java.lang.Object` | `put(java.lang.Object key, java.lang.Object value)` Puts a key-value mapping into this map.
`void` | `putAll(java.util.Map map)` Puts all the values from the specified map into this map.
`java.lang.Object` | `remove(java.lang.Object key)` Removes the specified mapping from this map.
`protected void` | `removeEntry(AbstractHashedMap.HashEntry entry, int hashIndex, AbstractHashedMap.HashEntry previous)` Removes an entry from the chain stored in a particular index.
`protected void` | `removeMapping(AbstractHashedMap.HashEntry entry, int hashIndex, AbstractHashedMap.HashEntry previous)` Removes a mapping from the map.
`protected void` | `reuseEntry(AbstractHashedMap.HashEntry entry, int hashIndex, int hashCode, java.lang.Object key, java.lang.Object value)` Reuses an existing key-value mapping, storing completely new data.
`int` | `size()` Gets the size of the map.
`java.lang.String` | `toString()` Gets the map as a String.
`protected void` | `updateEntry(AbstractHashedMap.HashEntry entry, java.lang.Object newValue)` Updates an existing key-value mapping to change the value.
`java.util.Collection` | `values()` Gets the values view of the map.

Methods inherited from class java.lang.Object
`finalize, getClass, notify, notifyAll, wait, wait, wait`

Field Detail

### NO_NEXT_ENTRY

    protected static final java.lang.String NO_NEXT_ENTRY

See Also:
  Constant Field Values

### NO_PREVIOUS_ENTRY

    protected static final java.lang.String NO_PREVIOUS_ENTRY

See Also:
  Constant Field Values

### REMOVE_INVALID

    protected static final java.lang.String REMOVE_INVALID

See Also:
  Constant Field Values

### GETKEY_INVALID

    protected static final java.lang.String GETKEY_INVALID

See Also:
  Constant Field Values

### GETVALUE_INVALID

    protected static final java.lang.String GETVALUE_INVALID

See Also:
  Constant Field Values

### SETVALUE_INVALID

    protected static final java.lang.String SETVALUE_INVALID

See Also:
  Constant Field Values

### DEFAULT_CAPACITY

    protected static final int DEFAULT_CAPACITY

  The default capacity to use

  See Also:
    Constant Field Values

### DEFAULT_THRESHOLD

    protected static final int DEFAULT_THRESHOLD

  The default threshold to use

  See Also:
    Constant Field Values

### DEFAULT_LOAD_FACTOR

    protected static final float DEFAULT_LOAD_FACTOR

  The default load factor to use

  See Also:
    Constant Field Values

### MAXIMUM_CAPACITY

    protected static final int MAXIMUM_CAPACITY

  The maximum capacity allowed

  See Also:
    Constant Field Values

### NULL

    protected static final java.lang.Object NULL

  An object for masking null

### loadFactor

    protected transient float loadFactor

  Load factor, normally 0.75

### size

    protected transient int size

  The size of the map

### data

    protected transient AbstractHashedMap.HashEntry[] data

  Map entries

### threshold

    protected transient int threshold

  Size at which to rehash

### modCount

    protected transient int modCount

  Modification count for iterators

### entrySet

    protected transient AbstractHashedMap.EntrySet entrySet

  Entry set

### keySet

    protected transient AbstractHashedMap.KeySet keySet

  Key set

### values

    protected transient AbstractHashedMap.Values values

  Values

Constructor Detail

### AbstractHashedMap

    protected AbstractHashedMap()

  Constructor only used in deserialization, do not use otherwise.

### AbstractHashedMap

    protected AbstractHashedMap(int initialCapacity,
                                float loadFactor,
                                int threshold)

  Constructor which performs no validation on the passed in parameters.

  Parameters:
    `initialCapacity` - the initial capacity, must be a power of two
    `loadFactor` - the load factor, must be > 0.0f and generally < 1.0f
    `threshold` - the threshold, must be sensible

### AbstractHashedMap

    protected AbstractHashedMap(int initialCapacity)

  Constructs a new, empty map with the specified initial capacity and default load factor.

  Parameters:
    `initialCapacity` - the initial capacity
  Throws:
    `java.lang.IllegalArgumentException` - if the initial capacity is less than one

### AbstractHashedMap

    protected AbstractHashedMap(int initialCapacity,
                                float loadFactor)

  Constructs a new, empty map with the specified initial capacity and load factor.

  Parameters:
    `initialCapacity` - the initial capacity
    `loadFactor` - the load factor
  Throws:
    `java.lang.IllegalArgumentException` - if the initial capacity is less than one
    `java.lang.IllegalArgumentException` - if the load factor is less than or equal to zero

### AbstractHashedMap

    protected AbstractHashedMap(java.util.Map map)

  Constructor copying elements from another map.

  Parameters:
    `map` - the map to copy
  Throws:
    `java.lang.NullPointerException` - if the map is null

Method Detail

### init

    protected void init()

  Initialise subclasses during construction, cloning or deserialization.

### get

    public java.lang.Object get(java.lang.Object key)

  Gets the value mapped to the key specified.

  Specified by:
    `get` in interface `java.util.Map`
  Overrides:
    `get` in class `java.util.AbstractMap`
  Parameters:
    `key` - the key
  Returns:
    the mapped value, null if no match

### size

    public int size()

  Gets the size of the map.

  Specified by:
    `size` in interface `java.util.Map`
  Overrides:
    `size` in class `java.util.AbstractMap`
  Returns:
    the size

### isEmpty

    public boolean isEmpty()

  Checks whether the map is currently empty.

  Specified by:
    `isEmpty` in interface `java.util.Map`
  Overrides:
    `isEmpty` in class `java.util.AbstractMap`
  Returns:
    true if the map is currently size zero

### containsKey

    public boolean containsKey(java.lang.Object key)

  Checks whether the map contains the specified key.

  Specified by:
    `containsKey` in interface `java.util.Map`
  Overrides:
    `containsKey` in class `java.util.AbstractMap`
  Parameters:
    `key` - the key to search for
  Returns:
    true if the map contains the key

### containsValue

    public boolean containsValue(java.lang.Object value)

  Checks whether the map contains the specified value.

  Specified by:
    `containsValue` in interface `java.util.Map`
  Overrides:
    `containsValue` in class `java.util.AbstractMap`
  Parameters:
    `value` - the value to search for
  Returns:
    true if the map contains the value

### put

    public java.lang.Object put(java.lang.Object key,
                                java.lang.Object value)

  Puts a key-value mapping into this map.

  Specified by:
    `put` in interface `java.util.Map`
  Overrides:
    `put` in class `java.util.AbstractMap`
  Parameters:
    `key` - the key to add
    `value` - the value to add
  Returns:
    the value previously mapped to this key, null if none

### putAll

    public void putAll(java.util.Map map)

  Puts all the values from the specified map into this map.

  This implementation iterates around the specified map and uses `put(Object, Object)`.

  Specified by:
    `putAll` in interface `java.util.Map`
  Overrides:
    `putAll` in class `java.util.AbstractMap`
  Parameters:
    `map` - the map to add
  Throws:
    `java.lang.NullPointerException` - if the map is null

### remove

    public java.lang.Object remove(java.lang.Object key)

  Removes the specified mapping from this map.

  Specified by:
    `remove` in interface `java.util.Map`
  Overrides:
    `remove` in class `java.util.AbstractMap`
  Parameters:
    `key` - the mapping to remove
  Returns:
    the value mapped to the removed key, null if key not in map

### clear

    public void clear()

  Clears the map, resetting the size to zero and nullifying references to avoid garbage collection issues.

  Specified by:
    `clear` in interface `java.util.Map`
  Overrides:
    `clear` in class `java.util.AbstractMap`

### convertKey

    protected java.lang.Object convertKey(java.lang.Object key)

  Converts input keys to another object for storage in the map. This implementation masks nulls. Subclasses can override this to perform alternate key conversions.

  The reverse conversion can be changed, if required, by overriding the getKey() method in the hash entry.

  Parameters:
    `key` - the key convert
  Returns:
    the converted key

### hash

    protected int hash(java.lang.Object key)

  Gets the hash code for the key specified. This implementation uses the additional hashing routine from JDK1.4. Subclasses can override this to return alternate hash codes.

  Parameters:
    `key` - the key to get a hash code for
  Returns:
    the hash code

### isEqualKey

    protected boolean isEqualKey(java.lang.Object key1,
                                 java.lang.Object key2)

  Compares two keys, in internal converted form, to see if they are equal. This implementation uses the equals method and assumes neither key is null. Subclasses can override this to match differently.

  Parameters:
    `key1` - the first key to compare passed in from outside
    `key2` - the second key extracted from the entry via `entry.key`
  Returns:
    true if equal

### isEqualValue

    protected boolean isEqualValue(java.lang.Object value1,
                                   java.lang.Object value2)

  Compares two values, in external form, to see if they are equal. This implementation uses the equals method and assumes neither value is null. Subclasses can override this to match differently.

  Parameters:
    `value1` - the first value to compare passed in from outside
    `value2` - the second value extracted from the entry via `getValue()`
  Returns:
    true if equal

### hashIndex

    protected int hashIndex(int hashCode,
                            int dataSize)

  Gets the index into the data storage for the hashCode specified. This implementation uses the least significant bits of the hashCode. Subclasses can override this to return alternate bucketing.

  Parameters:
    `hashCode` - the hash code to use
    `dataSize` - the size of the data to pick a bucket from
  Returns:
    the bucket index

### getEntry

    protected AbstractHashedMap.HashEntry getEntry(java.lang.Object key)

  Gets the entry mapped to the key specified.

  This method exists for subclasses that may need to perform a multi-step process accessing the entry. The public methods in this class don't use this method to gain a small performance boost.

  Parameters:
    `key` - the key
  Returns:
    the entry, null if no match

### updateEntry

    protected void updateEntry(AbstractHashedMap.HashEntry entry,
                               java.lang.Object newValue)

  Updates an existing key-value mapping to change the value.

  This implementation calls `setValue()` on the entry. Subclasses could override to handle changes to the map.

  Parameters:
    `entry` - the entry to update
    `newValue` - the new value to store

### reuseEntry

    protected void reuseEntry(AbstractHashedMap.HashEntry entry,
                              int hashIndex,
                              int hashCode,
                              java.lang.Object key,
                              java.lang.Object value)

  Reuses an existing key-value mapping, storing completely new data.

  This implementation sets all the data fields on the entry. Subclasses could populate additional entry fields.

  Parameters:
    `entry` - the entry to update, not null
    `hashIndex` - the index in the data array
    `hashCode` - the hash code of the key to add
    `key` - the key to add
    `value` - the value to add

### addMapping

    protected void addMapping(int hashIndex,
                              int hashCode,
                              java.lang.Object key,
                              java.lang.Object value)

  Adds a new key-value mapping into this map.

  This implementation calls `createEntry()`, `addEntry()` and `checkCapacity()`. It also handles changes to `modCount` and `size`. Subclasses could override to fully control adds to the map.

  Parameters:
    `hashIndex` - the index into the data array to store at
    `hashCode` - the hash code of the key to add
    `key` - the key to add
    `value` - the value to add

### createEntry

    protected AbstractHashedMap.HashEntry createEntry(AbstractHashedMap.HashEntry next,
                                                      int hashCode,
                                                      java.lang.Object key,
                                                      java.lang.Object value)

  Creates an entry to store the key-value data.

  This implementation creates a new HashEntry instance. Subclasses can override this to return a different storage class, or implement caching.

  Parameters:
    `next` - the next entry in sequence
    `hashCode` - the hash code to use
    `key` - the key to store
    `value` - the value to store
  Returns:
    the newly created entry

### addEntry

    protected void addEntry(AbstractHashedMap.HashEntry entry,
                            int hashIndex)

  Adds an entry into this map.

  This implementation adds the entry to the data storage table. Subclasses could override to handle changes to the map.

  Parameters:
    `entry` - the entry to add
    `hashIndex` - the index into the data array to store at

### removeMapping

    protected void removeMapping(AbstractHashedMap.HashEntry entry,
                                 int hashIndex,
                                 AbstractHashedMap.HashEntry previous)

  Removes a mapping from the map.

  This implementation calls `removeEntry()` and `destroyEntry()`. It also handles changes to `modCount` and `size`. Subclasses could override to fully control removals from the map.

  Parameters:
    `entry` - the entry to remove
    `hashIndex` - the index into the data structure
    `previous` - the previous entry in the chain

### removeEntry

    protected void removeEntry(AbstractHashedMap.HashEntry entry,
                               int hashIndex,
                               AbstractHashedMap.HashEntry previous)

  Removes an entry from the chain stored in a particular index.

  This implementation removes the entry from the data storage table. The size is not updated. Subclasses could override to handle changes to the map.

  Parameters:
    `entry` - the entry to remove
    `hashIndex` - the index into the data structure
    `previous` - the previous entry in the chain

### destroyEntry

    protected void destroyEntry(AbstractHashedMap.HashEntry entry)

  Kills an entry ready for the garbage collector.

  This implementation prepares the HashEntry for garbage collection. Subclasses can override this to implement caching (override clear as well).

  Parameters:
    `entry` - the entry to destroy

### checkCapacity

    protected void checkCapacity()

  Checks the capacity of the map and enlarges it if necessary.

  This implementation uses the threshold to check if the map needs enlarging

### ensureCapacity

    protected void ensureCapacity(int newCapacity)

  Changes the size of the data structure to the capacity proposed.

  Parameters:
    `newCapacity` - the new capacity of the array (a power of two, less or equal to max)

### calculateNewCapacity

    protected int calculateNewCapacity(int proposedCapacity)

  Calculates the new capacity of the map. This implementation normalizes the capacity to a power of two.

  Parameters:
    `proposedCapacity` - the proposed capacity
  Returns:
    the normalized new capacity

### calculateThreshold

    protected int calculateThreshold(int newCapacity,
                                     float factor)

  Calculates the new threshold of the map, where it will be resized. This implementation uses the load factor.

  Parameters:
    `newCapacity` - the new capacity
    `factor` - the load factor
  Returns:
    the new resize threshold

### entryNext

    protected AbstractHashedMap.HashEntry entryNext(AbstractHashedMap.HashEntry entry)

  Gets the `next` field from a `HashEntry`. Used in subclasses that have no visibility of the field.

  Parameters:
    `entry` - the entry to query, must not be null
  Returns:
    the `next` field of the entry
  Throws:
    `java.lang.NullPointerException` - if the entry is null
  Since:
    Commons Collections 3.1

### entryHashCode

    protected int entryHashCode(AbstractHashedMap.HashEntry entry)

  Gets the `hashCode` field from a `HashEntry`. Used in subclasses that have no visibility of the field.

  Parameters:
    `entry` - the entry to query, must not be null
  Returns:
    the `hashCode` field of the entry
  Throws:
    `java.lang.NullPointerException` - if the entry is null
  Since:
    Commons Collections 3.1

### entryKey

    protected java.lang.Object entryKey(AbstractHashedMap.HashEntry entry)

  Gets the `key` field from a `HashEntry`. Used in subclasses that have no visibility of the field.

  Parameters:
    `entry` - the entry to query, must not be null
  Returns:
    the `key` field of the entry
  Throws:
    `java.lang.NullPointerException` - if the entry is null
  Since:
    Commons Collections 3.1

### entryValue

    protected java.lang.Object entryValue(AbstractHashedMap.HashEntry entry)

  Gets the `value` field from a `HashEntry`. Used in subclasses that have no visibility of the field.

  Parameters:
    `entry` - the entry to query, must not be null
  Returns:
    the `value` field of the entry
  Throws:
    `java.lang.NullPointerException` - if the entry is null
  Since:
    Commons Collections 3.1

### mapIterator

    public MapIterator mapIterator()

  Gets an iterator over the map. Changes made to the iterator affect this map.

  A MapIterator returns the keys in the map. It also provides convenient methods to get the key and value, and set the value. It avoids the need to create an entrySet/keySet/values object. It also avoids creating the Map.Entry object.

  Specified by:
    `mapIterator` in interface `IterableMap`
  Returns:
    the map iterator

### entrySet

    public java.util.Set entrySet()

  Gets the entrySet view of the map. Changes made to the view affect this map. To simply iterate through the entries, use `mapIterator()`.

  Specified by:
    `entrySet` in interface `java.util.Map`
  Specified by:
    `entrySet` in class `java.util.AbstractMap`
  Returns:
    the entrySet view

### createEntrySetIterator

    protected java.util.Iterator createEntrySetIterator()

  Creates an entry set iterator. Subclasses can override this to return iterators with different properties.

  Returns:
    the entrySet iterator

### keySet

    public java.util.Set keySet()

  Gets the keySet view of the map. Changes made to the view affect this map. To simply iterate through the keys, use `mapIterator()`.

  Specified by:
    `keySet` in interface `java.util.Map`
  Overrides:
    `keySet` in class `java.util.AbstractMap`
  Returns:
    the keySet view

### createKeySetIterator

    protected java.util.Iterator createKeySetIterator()

  Creates a key set iterator. Subclasses can override this to return iterators with different properties.

  Returns:
    the keySet iterator

### values

    public java.util.Collection values()

  Gets the values view of the map. Changes made to the view affect this map. To simply iterate through the values, use `mapIterator()`.

  Specified by:
    `values` in interface `java.util.Map`
  Overrides:
    `values` in class `java.util.AbstractMap`
  Returns:
    the values view

### createValuesIterator

    protected java.util.Iterator createValuesIterator()

  Creates a values iterator. Subclasses can override this to return iterators with different properties.

  Returns:
    the values iterator

### doWriteObject

    protected void doWriteObject(java.io.ObjectOutputStream out)
                          throws java.io.IOException

  Writes the map data to the stream. This method must be overridden if a subclass must be setup before `put()` is used.

  Serialization is not one of the JDK's nicest topics. Normal serialization will initialise the superclass before the subclass. Sometimes however, this isn't what you want, as in this case the `put()` method on read can be affected by subclass state.

  The solution adopted here is to serialize the state data of this class in this protected method. This method must be called by the `writeObject()` of the first serializable subclass.

  Subclasses may override if they have a specific field that must be present on read before this implementation will work. Generally, the read determines what must be serialized here, if anything.

  Parameters:
    `out` - the output stream
  Throws:
    `java.io.IOException`

### doReadObject

    protected void doReadObject(java.io.ObjectInputStream in)
                         throws java.io.IOException,
                                java.lang.ClassNotFoundException

  Reads the map data from the stream. This method must be overridden if a subclass must be setup before `put()` is used.

  Serialization is not one of the JDK's nicest topics. Normal serialization will initialise the superclass before the subclass. Sometimes however, this isn't what you want, as in this case the `put()` method on read can be affected by subclass state.

  The solution adopted here is to deserialize the state data of this class in this protected method. This method must be called by the `readObject()` of the first serializable subclass.

  Subclasses may override if the subclass has a specific field that must be present before `put()` or `calculateThreshold()` will work correctly.

  Parameters:
    `in` - the input stream
  Throws:
    `java.io.IOException`
    `java.lang.ClassNotFoundException`

### clone

    protected java.lang.Object clone()

  Clones the map without cloning the keys or values.

  To implement `clone()`, a subclass must implement the `Cloneable` interface and make this method public.

  Overrides:
    `clone` in class `java.util.AbstractMap`
  Returns:
    a shallow clone

### equals

    public boolean equals(java.lang.Object obj)

  Compares this map with another.

  Specified by:
    `equals` in interface `java.util.Map`
  Overrides:
    `equals` in class `java.util.AbstractMap`
  Parameters:
    `obj` - the object to compare to
  Returns:
    true if equal

### hashCode

    public int hashCode()

  Gets the standard Map hashCode.

  Specified by:
    `hashCode` in interface `java.util.Map`
  Overrides:
    `hashCode` in class `java.util.AbstractMap`
  Returns:
    the hash code defined in the Map interface

### toString

    public java.lang.String toString()

  Gets the map as a String.

  Overrides:
    `toString` in class `java.util.AbstractMap`
  Returns:
    a string version of the map

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