Package org.forgerock.guava.common.collect

Interface Multiset<E>

All Superinterfaces:
Collection<E>, Iterable<E>
@GwtCompatible @Deprecated public interface Multiset<E> extends Collection<E>
Deprecated.
Use Multiset instead.
In order to maintain binary compatibility between product versions less than 6.5, which used forgerock-guava (a repackaged distribution of Guava 18.0) and version 6.5, this interface is copied from the guava project.

A collection that supports order-independent equality, like Set, but may have duplicate elements. A multiset is also sometimes called a bag.

Elements of a multiset that are equal to one another are referred to as occurrences of the same single element. The total number of occurrences of an element in a multiset is called the count of that element (the terms "frequency" and "multiplicity" are equivalent, but not used in this API). Since the count of an element is represented as an int, a multiset may never contain more than Integer.MAX_VALUE occurrences of any one element.

Multiset refines the specifications of several methods from Collection. It also defines an additional query operation, count(java.lang.Object), which returns the count of an element. There are five new bulk-modification operations, for example add(Object, int), to add or remove multiple occurrences of an element at once, or to set the count of an element to a specific value. These modification operations are optional, but implementations which support the standard collection operations add(Object) or remove(Object) are encouraged to implement the related methods as well. Finally, two collection views are provided: elementSet() contains the distinct elements of the multiset "with duplicates collapsed", and entrySet() is similar but contains Multiset.Entry instances, each providing both a distinct element and the count of that element.

In addition to these required methods, implementations of Multiset are expected to provide two static creation methods: create(), returning an empty multiset, and create(Iterable<? extends E>), returning a multiset containing the given initial elements. This is simply a refinement of Collection's constructor recommendations, reflecting the new developments of Java 5.

As with other collection types, the modification operations are optional, and should throw UnsupportedOperationException when they are not implemented. Most implementations should support either all add operations or none of them, all removal operations or none of them, and if and only if all of these are supported, the setCount methods as well.

A multiset uses Object.equals(java.lang.Object) to determine whether two instances should be considered "the same," unless specified otherwise by the implementation.

Common implementations include ImmutableMultiset, HashMultiset, and ConcurrentHashMultiset.

If your values may be zero, negative, or outside the range of an int, you may wish to use AtomicLongMap instead. Note, however, that unlike Multiset, AtomicLongMap does not automatically remove zeros.

See the Guava User Guide article on Multiset.

Since:
2.0 (imported from Google Collections Library)

  • Nested Class Summary

    Nested Classes
    Modifier and Type
    Interface
    Description
    static interface 
    Multiset.Entry<E>
    Deprecated.
    An unmodifiable element-count pair for a multiset.

  • Method Summary

    Modifier and Type
    Method
    Description
    boolean
    add(E element)
    Deprecated.
    Adds a single occurrence of the specified element to this multiset.
    int
    add(E element, int occurrences)
    Deprecated.
    Adds a number of occurrences of an element to this multiset.
    boolean
    contains(Object element)
    Deprecated.
    Determines whether this multiset contains the specified element.
    boolean
    containsAll(Collection<?> elements)
    Deprecated.
    Returns true if this multiset contains at least one occurrence of each element in the specified collection.
    int
    count(Object element)
    Deprecated.
    Returns the number of occurrences of an element in this multiset (the count of the element).
    Set<E>
    elementSet()
    Deprecated.
    Returns the set of distinct elements contained in this multiset.
    Set<Multiset.Entry<E>>
    entrySet()
    Deprecated.
    Returns a view of the contents of this multiset, grouped into Multiset.Entry instances, each providing an element of the multiset and the count of that element.
    boolean
    equals(Object object)
    Deprecated.
    Compares the specified object with this multiset for equality.
    int
    hashCode()
    Deprecated.
    Returns the hash code for this multiset.
    Iterator<E>
    iterator()
    Deprecated.
    boolean
    remove(Object element)
    Deprecated.
    Removes a single occurrence of the specified element from this multiset, if present.
    int
    remove(Object element, int occurrences)
    Deprecated.
    Removes a number of occurrences of the specified element from this multiset.
    boolean
    removeAll(Collection<?> c)
    Deprecated.
    boolean
    retainAll(Collection<?> c)
    Deprecated.
    int
    setCount(E element, int count)
    Deprecated.
    Adds or removes the necessary occurrences of an element such that the element attains the desired count.
    boolean
    setCount(E element, int oldCount, int newCount)
    Deprecated.
    Conditionally sets the count of an element to a new value, as described in setCount(Object, int), provided that the element has the expected current count.
    String
    toString()
    Deprecated.

    Methods inherited from interface java.util.Collection

    addAll, clear, isEmpty, parallelStream, removeIf, size, spliterator, stream, toArray, toArray, toArray

    Methods inherited from interface java.lang.Iterable

    forEach

  • Method Details

    • count

      int count(@Nullable Object element)
      Deprecated.
      Returns the number of occurrences of an element in this multiset (the count of the element). Note that for an Object.equals(java.lang.Object)-based multiset, this gives the same result as Collections.frequency(java.util.Collection<?>, java.lang.Object) (which would presumably perform more poorly).

      Note: the utility method Iterables#frequency generalizes this operation; it correctly delegates to this method when dealing with a multiset, but it can also accept any other iterable type.

      Parameters:
      element - the element to count occurrences of
      Returns:
      the number of occurrences of the element in this multiset; possibly zero but never negative

    • add

      int add(@Nullable E element, int occurrences)
      Deprecated.
      Adds a number of occurrences of an element to this multiset. Note that if occurrences == 1, this method has the identical effect to add(Object). This method is functionally equivalent (except in the case of overflow) to the call addAll(Collections.nCopies(element, occurrences)), which would presumably perform much more poorly.
      Parameters:
      element - the element to add occurrences of; may be null only if explicitly allowed by the implementation
      occurrences - the number of occurrences of the element to add. May be zero, in which case no change will be made.
      Returns:
      the count of the element before the operation; possibly zero
      Throws:
      IllegalArgumentException - if occurrences is negative, or if this operation would result in more than Integer.MAX_VALUE occurrences of the element
      NullPointerException - if element is null and this implementation does not permit null elements. Note that if occurrences is zero, the implementation may opt to return normally.

    • remove

      int remove(@Nullable Object element, int occurrences)
      Deprecated.
      Removes a number of occurrences of the specified element from this multiset. If the multiset contains fewer than this number of occurrences to begin with, all occurrences will be removed. Note that if occurrences == 1, this is functionally equivalent to the call remove(element).
      Parameters:
      element - the element to conditionally remove occurrences of
      occurrences - the number of occurrences of the element to remove. May be zero, in which case no change will be made.
      Returns:
      the count of the element before the operation; possibly zero
      Throws:
      IllegalArgumentException - if occurrences is negative

    • setCount

      int setCount(E element, int count)
      Deprecated.
      Adds or removes the necessary occurrences of an element such that the element attains the desired count.
      Parameters:
      element - the element to add or remove occurrences of; may be null only if explicitly allowed by the implementation
      count - the desired count of the element in this multiset
      Returns:
      the count of the element before the operation; possibly zero
      Throws:
      IllegalArgumentException - if count is negative
      NullPointerException - if element is null and this implementation does not permit null elements. Note that if count is zero, the implementor may optionally return zero instead.

    • setCount

      boolean setCount(E element, int oldCount, int newCount)
      Deprecated.
      Conditionally sets the count of an element to a new value, as described in setCount(Object, int), provided that the element has the expected current count. If the current count is not oldCount, no change is made.
      Parameters:
      element - the element to conditionally set the count of; may be null only if explicitly allowed by the implementation
      oldCount - the expected present count of the element in this multiset
      newCount - the desired count of the element in this multiset
      Returns:
      true if the condition for modification was met. This implies that the multiset was indeed modified, unless oldCount == newCount.
      Throws:
      IllegalArgumentException - if oldCount or newCount is negative
      NullPointerException - if element is null and the implementation does not permit null elements. Note that if oldCount and newCount are both zero, the implementor may optionally return true instead.

    • elementSet

      Set<E> elementSet()
      Deprecated.
      Returns the set of distinct elements contained in this multiset. The element set is backed by the same data as the multiset, so any change to either is immediately reflected in the other. The order of the elements in the element set is unspecified.

      If the element set supports any removal operations, these necessarily cause all occurrences of the removed element(s) to be removed from the multiset. Implementations are not expected to support the add operations, although this is possible.

      A common use for the element set is to find the number of distinct elements in the multiset: elementSet().size().

      Returns:
      a view of the set of distinct elements in this multiset

    • entrySet

      Set<Multiset.Entry<E>> entrySet()
      Deprecated.
      Returns a view of the contents of this multiset, grouped into Multiset.Entry instances, each providing an element of the multiset and the count of that element. This set contains exactly one entry for each distinct element in the multiset (thus it always has the same size as the elementSet()). The order of the elements in the element set is unspecified.

      The entry set is backed by the same data as the multiset, so any change to either is immediately reflected in the other. However, multiset changes may or may not be reflected in any Entry instances already retrieved from the entry set (this is implementation-dependent). Furthermore, implementations are not required to support modifications to the entry set at all, and the Entry instances themselves don't even have methods for modification. See the specific implementation class for more details on how its entry set handles modifications.

      Returns:
      a set of entries representing the data of this multiset

    • equals

      boolean equals(@Nullable Object object)
      Deprecated.
      Compares the specified object with this multiset for equality. Returns true if the given object is also a multiset and contains equal elements with equal counts, regardless of order.
      Specified by:
      equals in interface Collection<E>
      Overrides:
      equals in class Object

    • hashCode

      int hashCode()
      Deprecated.
      Returns the hash code for this multiset. This is defined as the sum of 
         

   ((element == null) ? 0 : element.hashCode()) ^ count(element)

      over all distinct elements in the multiset. It follows that a multiset and its entry set always have the same hash code.

      Specified by:
      hashCode in interface Collection<E>
      Overrides:
      hashCode in class Object

    • toString

      String toString()
      Deprecated.

      It is recommended, though not mandatory, that this method return the result of invoking toString() on the entrySet(), yielding a result such as [a x 3, c, d x 2, e].

      Overrides:
      toString in class Object

    • iterator

      Iterator<E> iterator()
      Deprecated.

      Elements that occur multiple times in the multiset will appear multiple times in this iterator, though not necessarily sequentially.

      Specified by:
      iterator in interface Collection<E>
      Specified by:
      iterator in interface Iterable<E>

    • contains

      boolean contains(@Nullable Object element)
      Deprecated.
      Determines whether this multiset contains the specified element.

      This method refines Collection.contains(java.lang.Object) to further specify that it may not throw an exception in response to element being null or of the wrong type.

      Specified by:
      contains in interface Collection<E>
      Parameters:
      element - the element to check for
      Returns:
      true if this multiset contains at least one occurrence of the element

    • containsAll

      boolean containsAll(Collection<?> elements)
      Deprecated.
      Returns true if this multiset contains at least one occurrence of each element in the specified collection.

      This method refines Collection.containsAll(java.util.Collection<?>) to further specify that it may not throw an exception in response to any of elements being null or of the wrong type.

      Note: this method does not take into account the occurrence count of an element in the two collections; it may still return true even if elements contains several occurrences of an element and this multiset contains only one. This is no different than any other collection type like List, but it may be unexpected to the user of a multiset.

      Specified by:
      containsAll in interface Collection<E>
      Parameters:
      elements - the collection of elements to be checked for containment in this multiset
      Returns:
      true if this multiset contains at least one occurrence of each element contained in elements
      Throws:
      NullPointerException - if elements is null

    • add

      boolean add(E element)
      Deprecated.
      Adds a single occurrence of the specified element to this multiset.

      This method refines Collection.add(E), which only ensures the presence of the element, to further specify that a successful call must always increment the count of the element, and the overall size of the collection, by one.

      Specified by:
      add in interface Collection<E>
      Parameters:
      element - the element to add one occurrence of; may be null only if explicitly allowed by the implementation
      Returns:
      true always, since this call is required to modify the multiset, unlike other Collection types
      Throws:
      NullPointerException - if element is null and this implementation does not permit null elements
      IllegalArgumentException - if Integer.MAX_VALUE occurrences of element are already contained in this multiset

    • remove

      boolean remove(@Nullable Object element)
      Deprecated.
      Removes a single occurrence of the specified element from this multiset, if present.

      This method refines Collection.remove(java.lang.Object) to further specify that it may not throw an exception in response to element being null or of the wrong type.

      Specified by:
      remove in interface Collection<E>
      Parameters:
      element - the element to remove one occurrence of
      Returns:
      true if an occurrence was found and removed

    • removeAll

      boolean removeAll(Collection<?> c)
      Deprecated.

      Note: This method ignores how often any element might appear in c, and only cares whether or not an element appears at all. If you wish to remove one occurrence in this multiset for every occurrence in c, see Multisets#removeOccurrences(Multiset, Multiset).

      This method refines Collection.removeAll(java.util.Collection<?>) to further specify that it may not throw an exception in response to any of elements being null or of the wrong type.

      Specified by:
      removeAll in interface Collection<E>

    • retainAll

      boolean retainAll(Collection<?> c)
      Deprecated.

      Note: This method ignores how often any element might appear in c, and only cares whether or not an element appears at all. If you wish to remove one occurrence in this multiset for every occurrence in c, see Multisets#retainOccurrences(Multiset, Multiset).

      This method refines Collection.retainAll(java.util.Collection<?>) to further specify that it may not throw an exception in response to any of elements being null or of the wrong type.

      Specified by:
      retainAll in interface Collection<E>
      See Also:
      • Multisets.retainOccurrences(com.google.common.collect.Multiset, com.google.common.collect.Multiset)