org.apache.commons.collections4

## Interface SetValuedMap<K,V>

- All Superinterfaces:
    MultiValuedMap<K,V>
  All Known Implementing Classes:
    AbstractSetValuedMap, HashSetValuedHashMap

      public interface SetValuedMap<K,V>
      extends MultiValuedMap<K,V>

  Defines a map that holds a set of values against each key.

  A `SetValuedMap` is a Map with slightly different semantics:

  - Putting a value into the map will add the value to a `Set` at that key.
  - Getting a value will return a `Set`, holding all the values put to that key.
  Since:
    4.1
  Version:
    $Id: SetValuedMap.java 1685299 2015-06-13 18:27:11Z tn $

- - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `Set<V>` | `get(K key)` Gets the set of values associated with the specified key.
    `Set<V>` | `remove(Object key)` Removes all values associated with the specified key.

    - ### Methods inherited from interface org.apache.commons.collections4.MultiValuedMap

      `asMap, clear, containsKey, containsMapping, containsValue, entries, isEmpty, keys, keySet, mapIterator, put, putAll, putAll, putAll, removeMapping, size, values`

- - ### Method Detail

    - #### get

          Set<V> get(K key)

      Gets the set of values associated with the specified key.

      Implementations typically return an empty `Set` if no values have been mapped to the key.

      Specified by:
        `get` in interface `MultiValuedMap<K,V>`
      Parameters:
        `key` - the key to retrieve
      Returns:
        the `Set` of values, implementations should return an empty `Set` for no mapping
      Throws:
        `NullPointerException` - if the key is null and null keys are invalid

    - #### remove

          Set<V> remove(Object key)

      Removes all values associated with the specified key.

      The returned set may be modifiable, but updates will not be propagated to this set-valued map. In case no mapping was stored for the specified key, an empty, unmodifiable set will be returned.

      Specified by:
        `remove` in interface `MultiValuedMap<K,V>`
      Parameters:
        `key` - the key to remove values from
      Returns:
        the `Set` of values removed, implementations should return null for no mapping found, but may return an empty collection
      Throws:
        `UnsupportedOperationException` - if the map is unmodifiable
        `NullPointerException` - if the key is null and null keys are invalid

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