Interface Multimap<K,​V>

    • Method Summary

      All Methods Instance Methods Abstract Methods Default Methods 
      Modifier and Type Method Description
      java.util.Map<K,​java.util.Collection<V>> asMap()
      Returns a view of this multimap as a Map from each distinct key to the nonempty collection of that key's associated values.
      void clear()
      Removes all key-value pairs from the multimap, leaving it empty.
      boolean containsEntry​(java.lang.Object key, java.lang.Object value)
      Returns true if this multimap contains at least one key-value pair with the key key and the value value.
      boolean containsKey​(java.lang.Object key)
      Returns true if this multimap contains at least one key-value pair with the key key.
      boolean containsValue​(java.lang.Object value)
      Returns true if this multimap contains at least one key-value pair with the value value.
      java.util.Collection<java.util.Map.Entry<K,​V>> entries()
      Returns a view collection of all key-value pairs contained in this multimap, as Map.Entry instances.
      boolean equals​(java.lang.Object obj)
      Compares the specified object with this multimap for equality.
      default void forEach​(java.util.function.BiConsumer<? super K,​? super V> action)
      Performs the given action for all key-value pairs contained in this multimap.
      java.util.Collection<V> get​(K key)
      Returns a view collection of the values associated with key in this multimap, if any.
      int hashCode()
      Returns the hash code for this multimap.
      boolean isEmpty()
      Returns true if this multimap contains no key-value pairs.
      Multiset<K> keys()
      Returns a view collection containing the key from each key-value pair in this multimap, without collapsing duplicates.
      java.util.Set<K> keySet()
      Returns a view collection of all distinct keys contained in this multimap.
      boolean put​(K key, V value)
      Stores a key-value pair in this multimap.
      boolean putAll​(Multimap<? extends K,​? extends V> multimap)
      Stores all key-value pairs of multimap in this multimap, in the order returned by multimap.entries().
      boolean putAll​(K key, java.lang.Iterable<? extends V> values)
      Stores a key-value pair in this multimap for each of values, all using the same key, key.
      boolean remove​(java.lang.Object key, java.lang.Object value)
      Removes a single key-value pair with the key key and the value value from this multimap, if such exists.
      java.util.Collection<V> removeAll​(java.lang.Object key)
      Removes all values associated with the key key.
      java.util.Collection<V> replaceValues​(K key, java.lang.Iterable<? extends V> values)
      Stores a collection of values with the same key, replacing any existing values for that key.
      int size()
      Returns the number of key-value pairs in this multimap.
      java.util.Collection<V> values()
      Returns a view collection containing the value from each key-value pair contained in this multimap, without collapsing duplicates (so values().size() == size()).
    • Method Detail

      • size

        int size()
        Returns the number of key-value pairs in this multimap.

        Note: this method does not return the number of distinct keys in the multimap, which is given by keySet().size() or asMap().size(). See the opening section of the Multimap class documentation for clarification.

      • isEmpty

        boolean isEmpty()
        Returns true if this multimap contains no key-value pairs. Equivalent to size() == 0, but can in some cases be more efficient.
      • containsKey

        boolean containsKey​(java.lang.Object key)
        Returns true if this multimap contains at least one key-value pair with the key key.
      • containsValue

        boolean containsValue​(java.lang.Object value)
        Returns true if this multimap contains at least one key-value pair with the value value.
      • containsEntry

        boolean containsEntry​(java.lang.Object key,
                              java.lang.Object value)
        Returns true if this multimap contains at least one key-value pair with the key key and the value value.
      • put

        boolean put​(K key,
                    V value)
        Stores a key-value pair in this multimap.

        Some multimap implementations allow duplicate key-value pairs, in which case put always adds a new key-value pair and increases the multimap size by 1. Other implementations prohibit duplicates, and storing a key-value pair that's already in the multimap has no effect.

        Returns:
        true if the method increased the size of the multimap, or false if the multimap already contained the key-value pair and doesn't allow duplicates
      • remove

        boolean remove​(java.lang.Object key,
                       java.lang.Object value)
        Removes a single key-value pair with the key key and the value value from this multimap, if such exists. If multiple key-value pairs in the multimap fit this description, which one is removed is unspecified.
        Returns:
        true if the multimap changed
      • putAll

        boolean putAll​(K key,
                       java.lang.Iterable<? extends V> values)
        Stores a key-value pair in this multimap for each of values, all using the same key, key. Equivalent to (but expected to be more efficient than):
        
         for (V value : values) {
           put(key, value);
         }
         

        In particular, this is a no-op if values is empty.

        Returns:
        true if the multimap changed
      • putAll

        boolean putAll​(Multimap<? extends K,​? extends V> multimap)
        Stores all key-value pairs of multimap in this multimap, in the order returned by multimap.entries().
        Returns:
        true if the multimap changed
      • replaceValues

        java.util.Collection<V> replaceValues​(K key,
                                              java.lang.Iterable<? extends V> values)
        Stores a collection of values with the same key, replacing any existing values for that key.

        If values is empty, this is equivalent to removeAll(key).

        Returns:
        the collection of replaced values, or an empty collection if no values were previously associated with the key. The collection may be modifiable, but updating it will have no effect on the multimap.
      • removeAll

        java.util.Collection<V> removeAll​(java.lang.Object key)
        Removes all values associated with the key key.

        Once this method returns, key will not be mapped to any values, so it will not appear in keySet(), asMap(), or any other views.

        Returns:
        the values that were removed (possibly empty). The returned collection may be modifiable, but updating it will have no effect on the multimap.
      • clear

        void clear()
        Removes all key-value pairs from the multimap, leaving it empty.
      • get

        java.util.Collection<V> get​(K key)
        Returns a view collection of the values associated with key in this multimap, if any. Note that when containsKey(key) is false, this returns an empty collection, not null.

        Changes to the returned collection will update the underlying multimap, and vice versa.

      • keySet

        java.util.Set<K> keySet()
        Returns a view collection of all distinct keys contained in this multimap. Note that the key set contains a key if and only if this multimap maps that key to at least one value.

        Changes to the returned set will update the underlying multimap, and vice versa. However, adding to the returned set is not possible.

      • keys

        Multiset<K> keys()
        Returns a view collection containing the key from each key-value pair in this multimap, without collapsing duplicates. This collection has the same size as this multimap, and keys().count(k) == get(k).size() for all k.

        Changes to the returned multiset will update the underlying multimap, and vice versa. However, adding to the returned collection is not possible.

      • values

        java.util.Collection<V> values()
        Returns a view collection containing the value from each key-value pair contained in this multimap, without collapsing duplicates (so values().size() == size()).

        Changes to the returned collection will update the underlying multimap, and vice versa. However, adding to the returned collection is not possible.

      • entries

        java.util.Collection<java.util.Map.Entry<K,​V>> entries()
        Returns a view collection of all key-value pairs contained in this multimap, as Map.Entry instances.

        Changes to the returned collection or the entries it contains will update the underlying multimap, and vice versa. However, adding to the returned collection is not possible.

      • forEach

        default void forEach​(java.util.function.BiConsumer<? super K,​? super V> action)
        Performs the given action for all key-value pairs contained in this multimap. If an ordering is specified by the Multimap implementation, actions will be performed in the order of iteration of entries(). Exceptions thrown by the action are relayed to the caller.

        To loop over all keys and their associated value collections, write Multimaps.asMap(multimap).forEach((key, valueCollection) -> action()).

        Since:
        21.0
      • asMap

        java.util.Map<K,​java.util.Collection<V>> asMap()
        Returns a view of this multimap as a Map from each distinct key to the nonempty collection of that key's associated values. Note that this.asMap().get(k) is equivalent to this.get(k) only when k is a key contained in the multimap; otherwise it returns null as opposed to an empty collection.

        Changes to the returned map or the collections that serve as its values will update the underlying multimap, and vice versa. The map does not support put or putAll, nor do its entries support setValue.

      • equals

        boolean equals​(java.lang.Object obj)
        Compares the specified object with this multimap for equality. Two multimaps are equal when their map views, as returned by asMap(), are also equal.

        In general, two multimaps with identical key-value mappings may or may not be equal, depending on the implementation. For example, two SetMultimap instances with the same key-value mappings are equal, but equality of two ListMultimap instances depends on the ordering of the values for each key.

        A non-empty SetMultimap cannot be equal to a non-empty ListMultimap, since their asMap() views contain unequal collections as values. However, any two empty multimaps are equal, because they both have empty asMap() views.

        Overrides:
        equals in class java.lang.Object
      • hashCode

        int hashCode()
        Returns the hash code for this multimap.

        The hash code of a multimap is defined as the hash code of the map view, as returned by asMap().

        In general, two multimaps with identical key-value mappings may or may not have the same hash codes, depending on the implementation. For example, two SetMultimap instances with the same key-value mappings will have the same hashCode, but the hashCode of ListMultimap instances depends on the ordering of the values for each key.

        Overrides:
        hashCode in class java.lang.Object