Package org.eclipse.collections.api.multimap

Interface Multimap<K,V>

Type Parameters:
K - the type of keys used
V - the type of mapped values
All Known Subinterfaces:
BagMultimap<K,V>, ImmutableBagIterableMultimap<K,V>, ImmutableBagMultimap<K,V>, ImmutableListMultimap<K,V>, ImmutableMultimap<K,V>, ImmutableSetIterableMultimap<K,V>, ImmutableSetMultimap<K,V>, ImmutableSortedBagMultimap<K,V>, ImmutableSortedSetMultimap<K,V>, ListMultimap<K,V>, MutableBagIterableMultimap<K,V>, MutableBagMultimap<K,V>, MutableListMultimap<K,V>, MutableMultimap<K,V>, MutableSetIterableMultimap<K,V>, MutableSetMultimap<K,V>, MutableSortedBagMultimap<K,V>, MutableSortedSetMultimap<K,V>, OrderedIterableMultimap<K,V>, ReversibleIterableMultimap<K,V>, SetMultimap<K,V>, SortedBagMultimap<K,V>, SortedIterableMultimap<K,V>, SortedSetMultimap<K,V>, UnsortedBagMultimap<K,V>, UnsortedSetMultimap<K,V>
All Known Implementing Classes:
AbstractImmutableMultimap, AbstractMultimap, AbstractMutableBagMultimap, AbstractMutableListMultimap, AbstractMutableMultimap, AbstractMutableSetMultimap, AbstractSynchronizedMultimap, AbstractSynchronizedPutMultimap, FastListMultimap, HashBagMultimap, HashBagMultimapWithHashingStrategy, ImmutableBagMultimapImpl, ImmutableListMultimapImpl, ImmutableSetMultimapImpl, ImmutableSortedBagMultimapImpl, ImmutableSortedSetMultimapImpl, MultiReaderFastListMultimap, MultiReaderHashBagMultimap, MultiReaderUnifiedSetMultimap, SynchronizedBagMultimap, SynchronizedListMultimap, SynchronizedPutFastListMultimap, SynchronizedPutHashBagMultimap, SynchronizedPutTreeSortedSetMultimap, SynchronizedPutUnifiedSetMultimap, SynchronizedSetMultimap, SynchronizedSortedBagMultimap, SynchronizedSortedSetMultimap, TreeBagMultimap, TreeBagMultimap, TreeBagMultimap, TreeSortedSetMultimap, UnifiedSetMultimap, UnifiedSetWithHashingStrategyMultimap
public interface Multimap<K,V>
This collection is a type of Map that can associate multiple values for keys.

Unlike Map however, this interface is read-only so the results of access methods such as get(Object) return a view onto the values associated with that key. The MutableMultimap sub-interface provides methods to mutate the collection.

The advantages to using this container over a Map<K, Collection<V>> is that all of the handling of the value collection can be done automatically. It also allows implementations to further specialize in how duplicate values will be handled. Value collections with list semantics would allow duplicate values for a key, while those implementing set semantics would not. The value collections can never be empty.

Internal iteration methods for keys and values (singly - forEachKey(Procedure), forEachValue(Procedure), and together - forEachKeyValue(Procedure2)), forEachKeyMultiValues(Procedure2)) are provided to allow flexible browsing of the collection's contents. Similarly, views also are provided for keys (keysView()), values (valuesView()) and the combination thereof (keyValuePairsView(), keyMultiValuePairsView()).

Since:
1.0

  • Method Details

    • newEmpty

      Multimap<K,V> newEmpty()
      Creates a new instance of the same implementation type, using the default capacity and growth parameters.

    • isEmpty

      boolean isEmpty()
      Returns true if there are no entries.

    • notEmpty

      boolean notEmpty()
      Returns true if there is at least one entry.

    • forEachValue

      void forEachValue(Procedure<? super V> procedure)
      Calls the procedure with each value.

      Given a Multimap with the contents:

      {"key1" : ["val1", "val2", "val2"], "key2" : ["val3"]}

      The given procedure would be invoked with the parameters:

      ["val1", "val2", "val2", "val3"]

    • forEachKey

      void forEachKey(Procedure<? super K> procedure)
      Calls the procedure with each key.

      Given a Multimap with the contents:

      {"key1" : ["val1", "val2", "val2"], "key2" : ["val3"]}

      The given procedure would be invoked with the parameters:

      ["key1", "key2"]

    • forEachKeyValue

      void forEachKeyValue(Procedure2<? super K,? super V> procedure)
      Calls the procedure with each key-value pair.

      Given a Multimap with the contents:

      {"key1" : ["val1", "val2", "val2"], "key2" : ["val3"]}

      The given procedure would be invoked with the parameters:

      [["key1", "val1"], ["key1", "val2"], ["key1", "val2"], ["key2", "val3"]]

    • forEachKeyMultiValues

      void forEachKeyMultiValues(Procedure2<? super K,? super RichIterable<V>> procedure)
      Calls the procedure with each key-Iterable[value].

      Given a Multimap with the contents:

      {"key1" : ["val1", "val2", "val2"], "key2" : ["val3"]}

      The given procedure would be invoked with the parameters:

      [["key1", {@link RichIterable["val1", "val2", "val2"]}], ["key2", {@link RichIterable["val3"]}]]

      Since:
      6.0

    • size

      int size()
      Returns the number of key-value entry pairs.

      This method is implemented with O(1) (constant-time) performance.

    • sizeDistinct

      int sizeDistinct()
      Returns the number of distinct keys.

    • containsKey

      boolean containsKey(Object key)
      Returns true if any values are mapped to the specified key.
      Parameters:
      key - the key to search for

    • containsValue

      boolean containsValue(Object value)
      Returns true if any key is mapped to the specified value.
      Parameters:
      value - the value to search for

    • containsKeyAndValue

      boolean containsKeyAndValue(Object key, Object value)
      Returns true if the specified key-value pair is mapped.
      Parameters:
      key - the key to search for
      value - the value to search for

    • get

      RichIterable<V> get(K key)
      Returns a view of all values associated with the given key.

      If the given key does not exist, an empty RichIterable is returned.

      Parameters:
      key - the key to search for

    • keysView

      RichIterable<K> keysView()
      Returns a lazy view of the unique keys.

    • keySet

      SetIterable<K> keySet()
      Returns an unmodifiable SetIterable of keys with O(1) complexity.

    • keyBag

      Bag<K> keyBag()
      Returns a Bag of keys with the count corresponding to the number of mapped values.

    • multiValuesView

      RichIterable<RichIterable<V>> multiValuesView()
      Returns an unmodifiable view of all the values mapped to each key.

    • valuesView

      RichIterable<V> valuesView()
      Returns a lazy flattened view of all the values.

    • keyMultiValuePairsView

      RichIterable<Pair<K,RichIterable<V>>> keyMultiValuePairsView()
      Returns a lazy view of the pair of a key and a lazy view of the values mapped to that key.

    • keyValuePairsView

      RichIterable<Pair<K,V>> keyValuePairsView()
      Returns a lazy view of all the key/value pairs.

    • toMap

      MutableMap<K,RichIterable<V>> toMap()
      Returns a new MutableMap of keys from this Multimap to the mapped values as a RichIterable.

    • toMap

      <R extends Collection<V>> MutableMap<K,R> toMap(Function0<R> collectionFactory)
      Returns a new MutableMap of keys from this Multimap to the mapped values as a RichIterable.
      Parameters:
      collectionFactory - used to create the collections that hold the values and affects the return type

    • equals

      boolean equals(Object obj)
      Compares the specified object with this Multimap for equality.

      Two Multimaps are equal when their map views (as returned by toMap()) are also equal.

      In general, two Multimaps with identical key-value mappings may or may not be equal, depending on the type of the collections holding the values. If the backing collections are Sets, then two instances with the same key-value mappings are equal, but if the backing collections are Lists, equality depends on the ordering of the values for each key.

      Any two empty Multimaps are equal, because they both have empty toMap() views.

      Overrides:
      equals in class 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 toMap().

      Overrides:
      hashCode in class Object

    • toMutable

      MutableMultimap<K,V> toMutable()
      Returns a mutable copy of this Multimap.

    • toImmutable

      ImmutableMultimap<K,V> toImmutable()
      Returns an immutable copy of this Multimap if it is not already immutable. If the Multimap is immutable, it will return itself.

      The returned Multimap will be Serializable if this Multimap is Serializable.

    • flip

      Multimap<V,K> flip()
      Given a Multimap from Domain -> Range return a multimap from Range -> Domain.
      Since:
      6.0

    • selectKeysValues

      Multimap<K,V> selectKeysValues(Predicate2<? super K,? super V> predicate)
      Returns all elements of the source multimap that satisfies the predicate. This method is also commonly called filter. 
      e.g.
 return multimap.selectKeysValues(new Predicate2<Integer, Person>()
 {
     public boolean accept(Integer age, Person person)
     {
         return (age >= 18)
                  && (person.getAddress().getCity().equals("Metuchen"));
     }
 });
      Parameters:
      predicate - a Predicate2 to use as the select criteria
      Returns:
      Multimap, which contains elements as a result of the select criteria
      Since:
      6.0

    • selectKeysValues

      <R extends MutableMultimap<K, V>> R selectKeysValues(Predicate2<? super K,? super V> predicate, R target)
      Same as the select method but uses the specified target multimap for the results. 
      e.g.
 return multimap.selectKeysValues(new Predicate2<Integer, Person>()
 {
     public boolean accept(Integer age, Person person)
     {
         return (age >= 18)
                  && (person.getAddress().getCity().equals("Metuchen"));
     }
 }, FastListMultimap.newMultimap());
      Parameters:
      predicate - a Predicate2 to use as the select criteria
      target - the Multimap to append to for all elements in this Multimap that satisfy the predicate
      Returns:
      target, which contains appended elements as a result of the select criteria
      Since:
      6.0

    • rejectKeysValues

      Multimap<K,V> rejectKeysValues(Predicate2<? super K,? super V> predicate)
      Returns all elements of the source multimap that don't satisfy the predicate. 
      e.g.
 return multimap.rejectKeysValues(new Predicate2<Integer, Person>()
 {
     public boolean accept(Integer age, Person person)
     {
         return (age >= 18)
                  && (person.getAddress().getCity().equals("Metuchen"));
     }
 });
      Parameters:
      predicate - a Predicate2 to use as the reject criteria
      Returns:
      Multimap, which contains elements that don't satisfy the predicate
      Since:
      6.0

    • rejectKeysValues

      <R extends MutableMultimap<K, V>> R rejectKeysValues(Predicate2<? super K,? super V> predicate, R target)
      Same as the reject method but uses the specified target multimap for the results. 
      e.g.
 return multimap.rejectKeysValues(new Predicate2<Integer, Person>()
 {
     public boolean accept(Integer age, Person person)
     {
         return (age >= 18)
                  && (person.getAddress().getCity().equals("Metuchen"));
     }
 }, FastListMultimap.newMultimap());
      Parameters:
      predicate - a Predicate2 to use as the reject criteria
      target - the Multimap to append to for all elements in this Multimap that don't satisfy the predicate
      Returns:
      target, which contains appended elements that don't satisfy the predicate
      Since:
      6.0

    • selectKeysMultiValues

      Multimap<K,V> selectKeysMultiValues(Predicate2<? super K,? super RichIterable<V>> predicate)
      Returns all elements of the source multimap that satisfies the predicate. This method is also commonly called filter. 
      e.g.
 return multimap.selectKeysMultiValues(new Predicate2<Integer, Iterable<Person>>()
 {
     public boolean accept(Integer age, Iterable<Person> values)
     {
         return (age >= 18)
                  && ((RichIterable<Person>)values.size() >= 2);
     }
 });
      Parameters:
      predicate - a Predicate2 to use as the select criteria
      Returns:
      Multimap, which contains elements as a result of the select criteria
      Since:
      6.0

    • selectKeysMultiValues

      <R extends MutableMultimap<K, V>> R selectKeysMultiValues(Predicate2<? super K,? super RichIterable<V>> predicate, R target)
      Same as the select method but uses the specified target multimap for the results. 
      e.g.
 return multimap.selectKeysMultiValues(new Predicate2<Integer, Iterable<Person>>()
 {
     public boolean accept(Integer age, Iterable<Person> values)
     {
         return (age >= 18)
                  && ((RichIterable<Person>)values.size() >= 2);
     }
 }, FastListMultimap.newMultimap());
      Parameters:
      predicate - a Predicate2 to use as the select criteria
      target - the Multimap to append to for all elements in this Multimap that satisfy the predicate
      Returns:
      target, which contains appended elements as a result of the select criteria
      Since:
      6.0

    • rejectKeysMultiValues

      Multimap<K,V> rejectKeysMultiValues(Predicate2<? super K,? super RichIterable<V>> predicate)
      Returns all elements of the source multimap that don't satisfy the predicate. 
      e.g.
 return multimap.rejectKeysMultiValues(new Predicate2<Integer, Iterable<Person>>()
 {
     public boolean accept(Integer age, Iterable<Person> values)
     {
         return (age >= 18)
                  && ((RichIterable<Person>)values.size() >= 2);
     }
 });
      Parameters:
      predicate - a Predicate2 to use as the reject criteria
      Returns:
      Multimap, which contains elements that don't satisfy the predicate
      Since:
      6.0

    • rejectKeysMultiValues

      <R extends MutableMultimap<K, V>> R rejectKeysMultiValues(Predicate2<? super K,? super RichIterable<V>> predicate, R target)
      Same as the reject method but uses the specified target multimap for the results. 
      e.g.
 return multimap.rejectKeysMultiValues(new Predicate2<Integer, Iterable<Person>>()
 {
     public boolean accept(Integer age, Iterable<Person> values)
     {
         return (age >= 18)
                  && ((RichIterable<Person>)values.size() >= 2);
     }
 }, FastListMultimap.newMultimap());
      Parameters:
      predicate - a Predicate2 to use as the reject criteria
      target - the Multimap to append to for all elements in this Multimap that don't satisfy the predicate
      Returns:
      target, which contains appended elements that don't satisfy the predicate
      Since:
      6.0

    • collectKeysValues

      <K2, V2> Multimap<K2,V2> collectKeysValues(Function2<? super K,? super V,Pair<K2,V2>> function)
      Returns a new multimap with the results of applying the specified function on each key and value of the source multimap. This method is also commonly called transform or map. 
      e.g.
 return multimap.collectKeysValues(new Function2<Integer, Person, Pair<String, String>>()
 {
     public Pair<String, String> valueOf(Integer age, Person person)
     {
         return Tuples.pair(age.toString(), person.getLastName());
     }
 });
      Parameters:
      function - a Function2 to use for transformation
      Returns:
      Multimap, which contains elements as a result of the transformation
      Since:
      6.0

    • collectKeysValues

      <K2, V2, R extends MutableMultimap<K2, V2>> R collectKeysValues(Function2<? super K,? super V,Pair<K2,V2>> function, R target)
      Same as the collect method but uses the specified target multimap for the results. 
      e.g.
 return multimap.collectKeysValues(new Function2<Integer, Person, Pair<String, String>>()
 {
     public Pair<String, String> valueOf(Integer age, Person person)
     {
         return Tuples.pair(age.toString(), person.getLastName());
     }
 }, HashBagMultimap.<String, String>newMultimap());
      Parameters:
      function - a Function2 to use for transformation
      target - the Multimap to append for all elements in this Multimap that are evaluated in function
      Returns:
      target, which contains appended elements as a result of the transformation
      Since:
      6.0

    • collectKeyMultiValues

      <K2, V2> Multimap<K2,V2> collectKeyMultiValues(Function<? super K,? extends K2> keyFunction, Function<? super V,? extends V2> valueFunction)
      Returns a new multimap with the results of applying the specified keyFunction and valueFunction on each key and corresponding values of the source multimap. This method is also commonly called transform or map. 
      e.g.
 return multimap.collectKeyMultiValues(each -> each + 1, Person::getLastName);
      Parameters:
      keyFunction - Function to use transformation to get the key
      valueFunction - Function to use transformation to get the values
      Returns:
      a new Multimap, which contains elements as a result of the transformation
      Since:
      10.0

    • collectKeyMultiValues

      <K2, V2, R extends MutableMultimap<K2, V2>> R collectKeyMultiValues(Function<? super K,? extends K2> keyFunction, Function<? super V,? extends V2> valueFunction, R target)
      Same as the collectKeyMultiValues method but uses the specified target multimap for the results. 
      e.g.
 return multimap.collectKeyMultiValues(each -> each + 1, Person::getLastName, HashBagMultimap.<Integer, String>newMultimap());
      Parameters:
      keyFunction - Function to use transformation to get the key
      valueFunction - Function to use transformation to get the values
      target - the Multimap to append for all elements in this Multimap that are evaluated in keyFunction and valueFunction
      Returns:
      target, which contains appended elements as a result of the transformation
      Since:
      10.0

    • collectValues

      <V2> Multimap<K,V2> collectValues(Function<? super V,? extends V2> function)
      Returns a new multimap with the results of applying the specified function on each value of the source multimap. This method is also commonly called transform or map. 
      e.g.
 return multimap.collectValues(new Function<Person, String>()
 {
     public String valueOf(Person person)
     {
         return person.getLastName();
     }
 });
      Parameters:
      function - a Function to use for transformation
      Returns:
      Multimap, which contains elements as a result of the transformation
      Since:
      6.0

    • collectValues

      <V2, R extends MutableMultimap<K, V2>> R collectValues(Function<? super V,? extends V2> function, R target)
      Same as the collect method but uses the specified target multimap for the results. 
      e.g.
 return multimap.collectValues(new Function<Person, String>()
 {
     public String valueOf(Person person)
     {
         return person.getLastName();
     }
 }, FastListMultimap.<Integer, String>newMultimap());
      Parameters:
      function - a Function to use for transformation
      target - the Multimap to append for all elements in this Multimap that are evaluated in function
      Returns:
      target, which contains appended elements as a result of the transformation
      Since:
      6.0