Package org.apache.commons.collections4

Interface MultiSet<E>

Type Parameters:
E - the type held in the multiset
All Superinterfaces:
Collection<E>, Iterable<E>
All Known Implementing Classes:
AbstractMapMultiSet, AbstractMultiSet, AbstractMultiSetDecorator, HashMultiSet, PredicatedMultiSet, SynchronizedMultiSet, UnmodifiableMultiSet
public interface MultiSet<E> extends Collection<E>
Defines a collection that counts the number of times an object appears in the collection.

Suppose you have a MultiSet that contains {a, a, b, c}. Calling getCount(Object) on a would return 2, while calling uniqueSet() would return {a, b, c}.

Since:
4.1

  • Nested Class Summary

    Nested Classes
    Modifier and Type
    Interface
    Description
    static interface 
    MultiSet.Entry<E>
    An unmodifiable entry for an element and its occurrence as contained in a MultiSet.

  • Method Summary

    Modifier and Type
    Method
    Description
    boolean
    add(E object)
    Adds one copy of the specified object to the MultiSet.
    int
    add(E object, int occurrences)
    Adds a number of occurrences of the specified object to the MultiSet.
    boolean
    containsAll(Collection<?> coll)
    Returns true if the MultiSet contains at least one occurrence for each element contained in the given collection.
    Set<MultiSet.Entry<E>>
    entrySet()
    Returns a Set of all entries contained in the MultiSet.
    boolean
    equals(Object obj)
    Compares this MultiSet to another object.
    int
    getCount(Object object)
    Returns the number of occurrences of the given object currently in the MultiSet.
    int
    hashCode()
    Gets a hash code for the MultiSet compatible with the definition of equals.
    Iterator<E>
    iterator()
    Returns an Iterator over the entire set of members, including copies due to cardinality.
    boolean
    remove(Object object)
    Removes one occurrence of the given object from the MultiSet.
    int
    remove(Object object, int occurrences)
    Removes a number of occurrences of the specified object from the MultiSet.
    boolean
    removeAll(Collection<?> coll)
    Remove all occurrences of all elements from this MultiSet represented in the given collection.
    boolean
    retainAll(Collection<?> coll)
    Remove any elements of this MultiSet that are not contained in the given collection.
    int
    setCount(E object, int count)
    Sets the number of occurrences of the specified object in the MultiSet to the given count.
    int
    size()
    Returns the total number of items in the MultiSet.
    Set<E>
    uniqueSet()
    Returns a Set of unique elements in the MultiSet.

    Methods inherited from interface java.util.Collection

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

    Methods inherited from interface java.lang.Iterable

    forEach

  • Method Details

    • add

      boolean add(E object)
      Adds one copy of the specified object to the MultiSet.

      If the object is already in the uniqueSet() then increment its count as reported by getCount(Object). Otherwise, add it to the uniqueSet() and report its count as 1.

      Specified by:
      add in interface Collection<E>
      Parameters:
      object - the object to add
      Returns:
      true always, as the size of the MultiSet is increased in any case

    • add

      int add(E object, int occurrences)
      Adds a number of occurrences of the specified object to the MultiSet.

      If the object is already in the uniqueSet() then increment its count as reported by getCount(Object). Otherwise, add it to the uniqueSet() and report its count as occurrences.

      Parameters:
      object - the object to add
      occurrences - the number of occurrences to add, may be zero, in which case no change is made to the multiset
      Returns:
      the number of occurrences of the object in the multiset before this operation; possibly zero
      Throws:
      IllegalArgumentException - if occurrences is negative

    • containsAll

      boolean containsAll(Collection<?> coll)
      Returns true if the MultiSet contains at least one occurrence for each element contained in the given collection.
      Specified by:
      containsAll in interface Collection<E>
      Parameters:
      coll - the collection to check against
      Returns:
      true if the MultiSet contains all the collection

    • entrySet

      Set<MultiSet.Entry<E>> entrySet()
      Returns a Set of all entries contained in the MultiSet.

      The returned set is backed by this multiset, so any change to either is immediately reflected in the other.

      Returns:
      the Set of MultiSet entries

    • equals

      boolean equals(Object obj)
      Compares this MultiSet to another object.

      This MultiSet equals another object if it is also a MultiSet that contains the same number of occurrences of the same elements.

      Specified by:
      equals in interface Collection<E>
      Overrides:
      equals in class Object
      Parameters:
      obj - the object to compare to
      Returns:
      true if equal

    • getCount

      int getCount(Object object)
      Returns the number of occurrences of the given object currently in the MultiSet. If the object does not exist in the multiset, return 0.
      Parameters:
      object - the object to search for
      Returns:
      the number of occurrences of the object, zero if not found

    • hashCode

      int hashCode()
      Gets a hash code for the MultiSet compatible with the definition of equals. The hash code is defined as the sum total of a hash code for each element. The per element hash code is defined as (e==null ? 0 : e.hashCode()) ^ noOccurrences).
      Specified by:
      hashCode in interface Collection<E>
      Overrides:
      hashCode in class Object
      Returns:
      the hash code of the MultiSet

    • iterator

      Iterator<E> iterator()
      Returns an Iterator over the entire set of members, including copies due to cardinality. This iterator is fail-fast and will not tolerate concurrent modifications.
      Specified by:
      iterator in interface Collection<E>
      Specified by:
      iterator in interface Iterable<E>
      Returns:
      iterator over all elements in the MultiSet

    • remove

      boolean remove(Object object)
      Removes one occurrence of the given object from the MultiSet.

      If the number of occurrences after this operation is reduced to zero, the object will be removed from the uniqueSet().

      Specified by:
      remove in interface Collection<E>
      Parameters:
      object - the object to remove
      Returns:
      true if this call changed the collection

    • remove

      int remove(Object object, int occurrences)
      Removes a number of occurrences of the specified object from the MultiSet.

      If the number of occurrences to remove is greater than the actual number of occurrences in the multiset, the object will be removed from the multiset.

      Parameters:
      object - the object to remove
      occurrences - the number of occurrences to remove, may be zero, in which case no change is made to the multiset
      Returns:
      the number of occurrences of the object in the multiset before the operation; possibly zero
      Throws:
      IllegalArgumentException - if occurrences is negative

    • removeAll

      boolean removeAll(Collection<?> coll)
      Remove all occurrences of all elements from this MultiSet represented in the given collection.
      Specified by:
      removeAll in interface Collection<E>
      Parameters:
      coll - the collection of elements to remove
      Returns:
      true if this call changed the multiset

    • retainAll

      boolean retainAll(Collection<?> coll)
      Remove any elements of this MultiSet that are not contained in the given collection.
      Specified by:
      retainAll in interface Collection<E>
      Parameters:
      coll - the collection of elements to retain
      Returns:
      true if this call changed the multiset

    • setCount

      int setCount(E object, int count)
      Sets the number of occurrences of the specified object in the MultiSet to the given count.

      If the provided count is zero, the object will be removed from the uniqueSet().

      Parameters:
      object - the object to update
      count - the number of occurrences of the object
      Returns:
      the number of occurrences of the object before this operation, zero if the object was not contained in the multiset
      Throws:
      IllegalArgumentException - if count is negative

    • size

      int size()
      Returns the total number of items in the MultiSet.
      Specified by:
      size in interface Collection<E>
      Returns:
      the total size of the multiset

    • uniqueSet

      Set<E> uniqueSet()
      Returns a Set of unique elements in the MultiSet.

      Uniqueness constraints are the same as those in Set.

      The returned set is backed by this multiset, so any change to either is immediately reflected in the other. Only removal operations are supported, in which case all occurrences of the element are removed from the backing multiset.

      Returns:
      the Set of unique MultiSet elements