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## com.neoworks.util
Class HashMapMultiMap

    java.lang.Object
      |
      +--com.neoworks.util.HashMapMultiMap

All Implemented Interfaces:
  MultiMap

public class HashMapMultiMap
extends java.lang.Object
implements MultiMap

HashMapMultiMap is a Multimap backed by a `HashMap` of `Set` objects. This means it differs from a standard MultiMap in a few important ways.

- It cannot contain duplicate entries in the keys
- It cannot contain duplicates in the values
- It might even be in any way quick

Version:
  $Revision: 1.2 $
Author:
  nick@neoworks.com

Nested Class Summary

Nested classes inherited from class com.neoworks.util.MultiMap
`MultiMap.Entry`

Constructor Summary
`HashMapMultiMap()` Public constructor

Method Summary
`void` | `clear()` Removes all mappings from this multimap (optional operation).
`boolean` | `containsKey(java.lang.Object key)` Returns `true` if this multimap contains a mapping for the specified key.
`boolean` | `containsValue(java.lang.Object value)` Returns true if this multimap maps one or more keys to the specified value.
`java.util.Set` | `entrySet()` Get the EntrySet.
`boolean` | `equals(java.lang.Object o)` Compares the specified object with this multimap for equality.
`java.util.Set` | `get(java.lang.Object key)` Returns the set of values to which this multimap maps the specified key.
`int` | `hashCode()` Returns the hash code value for this multimap.
`boolean` | `isEmpty()` Returns `true` if this multimap contains no key-value mappings.
`java.util.Collection` | `keys()` Returns a collection view of the keys contained in this multimap.
`java.util.Set` | `put(java.lang.Object key, java.lang.Object value)` Associates the specified value with the specified key in this multimap (optional operation).
`void` | `putAll(MultiMap multimap)` Copies all of the mappings from the specified multimap to this multimap (optional operation).
`java.util.Set` | `remove(java.lang.Object key)` Removes all the mappings for this key from this multimap if present (optional operation).
`java.lang.Object` | `remove(java.lang.Object key, java.lang.Object value)` Removes the (key, value) mapping from this multimap if present (optional operation).
`int` | `size()` Returns the number of key-values mappings in this multimap.
`java.util.Collection` | `uniqueKeys()` Returns a collection of the unique keys in this multimap.
`java.util.Collection` | `values()` Returns a collection view of the values contained in this multimap.

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

Constructor Detail

### HashMapMultiMap

    public HashMapMultiMap()

  Public constructor

Method Detail

### put

    public java.util.Set put(java.lang.Object key,
                             java.lang.Object value)
                      throws java.lang.UnsupportedOperationException,
                             java.lang.ClassCastException,
                             java.lang.IllegalArgumentException,
                             java.lang.NullPointerException

  Associates the specified value with the specified key in this multimap (optional operation). If the multimap previously contained a mapping for this key this mapping is not lost.

  Specified by:
    `put` in interface `MultiMap`
  Parameters:
    `key` - Key with which the specified value is to be associated.
    `value` - Value to be associated with the specified key.
  Returns:
    `Set` of values associated with the specified key (including the new addition).
  Throws:
    `java.lang.UnsupportedOperationException` - If the put operation is not supported by this multimap.
    `java.lang.ClassCastException` - If the class of the specified key or value prevents it from being stored in this multimap.
    `java.lang.IllegalArgumentException` - If some aspect of this key or value prevents it from being stored in this multimap.
    `java.lang.NullPointerException` - This multimap does not permit `null` keys or values, and the specified key or value is `null`.

### keys

    public java.util.Collection keys()

  Returns a collection view of the keys contained in this multimap. The collection is backed by the multimap, so changes to the multimap are reflected in the collection, and vice-versa. If the multimap is modified while an iteration over the collection is in progress, the results of the iteration are undefined. The collection supports element removal, which removes the corresponding mapping from the multimap, via the `Iterator.remove`, `Collection.remove`, `removeAll` `retainAll`, and `clear` operations. It does not support the `add` or `addAll` operations. This implementation does not return duplicate keys in the keyset.

  Specified by:
    `keys` in interface `MultiMap`
  Returns:
    A collection view of the keys contained in this multimap.

### remove

    public java.util.Set remove(java.lang.Object key)
                         throws java.lang.UnsupportedOperationException

  Removes all the mappings for this key from this multimap if present (optional operation).

  Specified by:
    `remove` in interface `MultiMap`
  Parameters:
    `key` - Key whose mappings is to be removed from the multimap.
  Returns:
    `Set` of values associated with the specified key, or `null` if there were no mappings for key.
  Throws:
    `java.lang.UnsupportedOperationException` - If the remove operation is not supported by this multimap.

### clear

    public void clear()
               throws java.lang.UnsupportedOperationException

  Removes all mappings from this multimap (optional operation).

  Specified by:
    `clear` in interface `MultiMap`
  Throws:
    `java.lang.UnsupportedOperationException` - If clear is not supported by this multimap.

### values

    public java.util.Collection values()

  Returns a collection view of the values contained in this multimap. The collection is backed by the multimap, so changes to the multimap are reflected in the collection, and vice-versa. If the multimap is modified while an iteration over the collection is in progress, the results of the iteration are undefined. The collection supports element removal, which removes the corresponding mapping from the multimap, via the `Iterator.remove`, `Collection.remove`, `removeAll`, `retainAll` and `clear` operations. It does not support the `add` or `addAll` operations.

  Specified by:
    `values` in interface `MultiMap`
  Returns:
    A collection view of the values contained in this multimap.

### entrySet

    public java.util.Set entrySet()

  Get the EntrySet. This is pretty pointless for this particular implementation, but is included because it's in the interface.

  Specified by:
    `entrySet` in interface `MultiMap`
  Returns:
    A set of entries

### hashCode

    public int hashCode()

  Returns the hash code value for this multimap. The hash code of a multimap is defined to be the sum of the `hashCodes` of each entry in the multimap's `entrySet` view. This ensures that `t1.equals(t2)` implies that `t1.hashCode()==t2.hashCode()` for any two multimaps t1 and t2, as required by the general contract of `Object.hashCode`.

  Specified by:
    `hashCode` in interface `MultiMap`
  Overrides:
    `hashCode` in class `java.lang.Object`
  Returns:
    The hash code value for this multimap.

### containsKey

    public boolean containsKey(java.lang.Object key)
                        throws java.lang.ClassCastException,
                               java.lang.NullPointerException

  Returns `true` if this multimap contains a mapping for the specified key.

  Specified by:
    `containsKey` in interface `MultiMap`
  Parameters:
    `key` - Key whose presence in this multimap is to be tested.
  Returns:
    `true` if this multimap contains a mapping for the specified key.
  Throws:
    `java.lang.ClassCastException` - If the key is of an inappropriate type for this multimap.
    `java.lang.NullPointerException` - If the key is null and this multimap does not not permit null keys

### putAll

    public void putAll(MultiMap multimap)
                throws java.lang.UnsupportedOperationException,
                       java.lang.ClassCastException,
                       java.lang.IllegalArgumentException,
                       java.lang.NullPointerException

  Copies all of the mappings from the specified multimap to this multimap (optional operation). These mappings will replace any mappings that this multimap had for any of the keys currently in the specified multimap.

  Specified by:
    `putAll` in interface `MultiMap`
  Parameters:
    `multimap` - Mappings to be stored in this multimap.
  Throws:
    `java.lang.UnsupportedOperationException` - If the put operation is not supported by this multimap.
    `java.lang.ClassCastException` - If the class of the specified key or value prevents it from being stored in this multimap.
    `java.lang.IllegalArgumentException` - If some aspect of a key or value in the specified multimap prevents it from being stored in this multimap.
    `java.lang.NullPointerException` - This multimap does not permit `null` keys or values, and the specified key or value is `null`.

### size

    public int size()

  Returns the number of key-values mappings in this multimap. If the multimap contains more than `Integer.MAX_VALUE` elements, returns `Integer.MAX_VALUE`.

  Specified by:
    `size` in interface `MultiMap`
  Returns:
    The number of key-values mappings in this multimap

### uniqueKeys

    public java.util.Collection uniqueKeys()

  Returns a collection of the unique keys in this multimap.

  Specified by:
    `uniqueKeys` in interface `MultiMap`
  Returns:
    A Collection of unique keys

### remove

    public java.lang.Object remove(java.lang.Object key,
                                   java.lang.Object value)
                            throws java.lang.UnsupportedOperationException

  Removes the (key, value) mapping from this multimap if present (optional operation).

  Specified by:
    `remove` in interface `MultiMap`
  Parameters:
    `value` - The value associated with the key to identify the item to remove
    `key` - Key whose mapping to the value is to be removed from the multimap.
  Returns:
    Value that was unmapped from the specified key, or `null` if the given mapping did not exist.
  Throws:
    `java.lang.UnsupportedOperationException` - If the remove operation is not supported by this multimap.

### containsValue

    public boolean containsValue(java.lang.Object value)

  Returns true if this multimap maps one or more keys to the specified value. More formally, returns true if and only if this multimap contains at least one mapping to a value v such that `(value==null ? v==null : value.equals(v))`. This operation will probably require time linear in the multimap size for most implementations of the `MultiMap` interface.

  Specified by:
    `containsValue` in interface `MultiMap`
  Parameters:
    `value` - Value whose presence in this multimap is to be tested.
  Returns:
    `true` if this multimap maps one or more keys to the specified value.

### equals

    public boolean equals(java.lang.Object o)

  Compares the specified object with this multimap for equality. Returns true if the given object is also a multimap and the two multimaps represent the same mappings. More formally, two maps t1 and t2 represent the same mappings if `t1.entrySet().equals(t2.entrySet())`. This ensures that the equals method works properly across different implementations of the `MultiMap` interface.

  Specified by:
    `equals` in interface `MultiMap`
  Overrides:
    `equals` in class `java.lang.Object`
  Parameters:
    `o` - Object to be compared for equality with this multimap.
  Returns:
    `true` if the specified object is equal to this multimap.

### get

    public java.util.Set get(java.lang.Object key)
                      throws java.lang.ClassCastException,
                             java.lang.NullPointerException

  Returns the set of values to which this multimap maps the specified key. Returns null if the multimap contains no mappings for this key. A return value of `null` does indicate that the multimap contains no mappings for the key; it's possible that the multimap explicitly maps the key to null, in this case the returned set will contain `null` possibly along with other objects. The `containsKey` operation may also be used to distinguish these two cases.

  Specified by:
    `get` in interface `MultiMap`
  Parameters:
    `key` - Key whose associated value is to be returned.
  Returns:
    A `Set` of values to which this multimap maps the specified key, or `null` if the multimap contains no mapping for this key.
  Throws:
    `java.lang.ClassCastException` - If the key is of an inappropriate type for this multimap.
    `java.lang.NullPointerException` - If the key is `null` and this multimap does not not permit`null` keys

### isEmpty

    public boolean isEmpty()

  Returns `true` if this multimap contains no key-value mappings.

  Specified by:
    `isEmpty` in interface `MultiMap`
  Returns:
    `true` if this multimap contains no key-value mappings.

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