Package com.google.common.collect

Class ConcurrentHashMultiset<E>

  • All Implemented Interfaces:
    Multiset<E>, java.io.Serializable, java.lang.Iterable<E>, java.util.Collection<E>
    public final class ConcurrentHashMultiset<E>
extends java.util.AbstractCollection<E>
implements java.io.Serializable
    A multiset that supports concurrent modifications and that provides atomic versions of most Multiset operations (exceptions where noted). Null elements are not supported.

    See the Guava User Guide article on Multiset.

    Since:
    2.0 (imported from Google Collections Library)
    See Also:
    Serialized Form

    • Nested Class Summary

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      boolean add​(E element)
      Adds a single occurrence of the specified element to this multiset.
      int add​(E element, int occurrences)
      Adds a number of occurrences of the specified element to this multiset.
      boolean addAll​(java.util.Collection<? extends E> elementsToAdd)
      void clear()  
      boolean contains​(java.lang.Object element)
      Determines whether this multiset contains the specified element.
      int count​(java.lang.Object element)
      Returns the number of occurrences of element in this multiset.
      static <E> ConcurrentHashMultiset<E> create()
      Creates a new, empty ConcurrentHashMultiset using the default initial capacity, load factor, and concurrency settings.
      static <E> ConcurrentHashMultiset<E> create​(MapMaker mapMaker)
      Creates a new, empty ConcurrentHashMultiset using mapMaker to construct the internal backing map.
      static <E> ConcurrentHashMultiset<E> create​(java.lang.Iterable<? extends E> elements)
      Creates a new ConcurrentHashMultiset containing the specified elements, using the default initial capacity, load factor, and concurrency settings.
      java.util.Set<E> elementSet()
      Returns the set of distinct elements contained in this multiset.
      java.util.Set<Multiset.Entry<E>> entrySet()
      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​(java.lang.Object object)
      Compares the specified object with this multiset for equality.
      int hashCode()
      Returns the hash code for this multiset.
      boolean isEmpty()  
      java.util.Iterator<E> iterator()
      boolean remove​(java.lang.Object element)
      Removes a single occurrence of the specified element from this multiset, if present.
      int remove​(java.lang.Object element, int occurrences)
      Removes a number of occurrences of the specified element from this multiset.
      boolean removeAll​(java.util.Collection<?> elementsToRemove)
      boolean removeExactly​(java.lang.Object element, int occurrences)
      Removes exactly the specified number of occurrences of element, or makes no change if this is not possible.
      boolean retainAll​(java.util.Collection<?> elementsToRetain)
      int setCount​(E element, int count)
      Adds or removes occurrences of element such that the count(java.lang.Object) of the element becomes count.
      boolean setCount​(E element, int expectedOldCount, int newCount)
      Sets the number of occurrences of element to newCount, but only if the count is currently expectedOldCount.
      int size()
      java.lang.Object[] toArray()  
      <T> T[] toArray​(T[] array)  
      java.lang.String toString()

      • Methods inherited from class java.util.AbstractCollection

        containsAll

      • Methods inherited from class java.lang.Object

        getClass, notify, notifyAll, wait, wait, wait

      • Methods inherited from interface java.util.Collection

        parallelStream, removeIf, spliterator, stream, toArray

      • Methods inherited from interface java.lang.Iterable

        forEach

    • Method Detail

      • create

        public static <E> ConcurrentHashMultiset<E> create()
        Creates a new, empty ConcurrentHashMultiset using the default initial capacity, load factor, and concurrency settings.

      • create

        public static <E> ConcurrentHashMultiset<E> create​(java.lang.Iterable<? extends E> elements)
        Creates a new ConcurrentHashMultiset containing the specified elements, using the default initial capacity, load factor, and concurrency settings.

        This implementation is highly efficient when elements is itself a Multiset.

        Parameters:
        elements - the elements that the multiset should contain

      • create

        @Beta
public static <E> ConcurrentHashMultiset<E> create​(MapMaker mapMaker)
        Creates a new, empty ConcurrentHashMultiset using mapMaker to construct the internal backing map.

        If this MapMaker is configured to use entry eviction of any kind, this eviction applies to all occurrences of a given element as a single unit. However, most updates to the multiset do not count as map updates at all, since we're usually just mutating the value stored in the map, so MapMaker.expireAfterAccess(long, java.util.concurrent.TimeUnit) makes sense (evict the entry that was queried or updated longest ago), but MapMaker.expireAfterWrite(long, java.util.concurrent.TimeUnit) doesn't, because the eviction time is measured from when we saw the first occurrence of the object.

        The returned multiset is serializable but any serialization caveats given in MapMaker apply.

        Finally, soft/weak values can be used but are not very useful: the values are created internally and not exposed externally, so no one else will have a strong reference to the values. Weak keys on the other hand can be useful in some scenarios.

        Since:
        15.0 (source compatible (accepting the since removed GenericMapMaker class) since 7.0)

      • count

        public int count​(@Nullable
                 java.lang.Object element)
        Returns the number of occurrences of element in this multiset.
        Specified by:
        count in interface Multiset<E>
        Parameters:
        element - the element to look for
        Returns:
        the nonnegative number of occurrences of the element

      • size

        public int size()

        If the data in the multiset is modified by any other threads during this method, it is undefined which (if any) of these modifications will be reflected in the result.

        Specified by:
        size in interface java.util.Collection<E>

      • toArray

        public java.lang.Object[] toArray()
        Specified by:
        toArray in interface java.util.Collection<E>
        Overrides:
        toArray in class java.util.AbstractCollection<E>

      • toArray

        public <T> T[] toArray​(T[] array)
        Specified by:
        toArray in interface java.util.Collection<E>
        Overrides:
        toArray in class java.util.AbstractCollection<E>

      • add

        public int add​(E element,
               int occurrences)
        Adds a number of occurrences of the specified element to this multiset.
        Specified by:
        add in interface Multiset<E>
        Parameters:
        element - the element to add
        occurrences - the number of occurrences to add
        Returns:
        the previous count of the element before the operation; possibly zero
        Throws:
        java.lang.IllegalArgumentException - if occurrences is negative, or if the resulting amount would exceed Integer.MAX_VALUE

      • remove

        public int remove​(@Nullable
                  java.lang.Object element,
                  int occurrences)
        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.
        Specified by:
        remove in interface Multiset<E>
        Parameters:
        element - the element whose occurrences should be removed
        occurrences - the number of occurrences of the element to remove
        Returns:
        the count of the element before the operation; possibly zero
        Throws:
        java.lang.IllegalArgumentException - if occurrences is negative

      • removeExactly

        public boolean removeExactly​(@Nullable
                             java.lang.Object element,
                             int occurrences)
        Removes exactly the specified number of occurrences of element, or makes no change if this is not possible.

        This method, in contrast to remove(Object, int), has no effect when the element count is smaller than occurrences.

        Parameters:
        element - the element to remove
        occurrences - the number of occurrences of element to remove
        Returns:
        true if the removal was possible (including if occurrences is zero)

      • setCount

        public int setCount​(E element,
                    int count)
        Adds or removes occurrences of element such that the count(java.lang.Object) of the element becomes count.
        Specified by:
        setCount in interface Multiset<E>
        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 element in the multiset before this call
        Throws:
        java.lang.IllegalArgumentException - if count is negative

      • setCount

        public boolean setCount​(E element,
                        int expectedOldCount,
                        int newCount)
        Sets the number of occurrences of element to newCount, but only if the count is currently expectedOldCount. If element does not appear in the multiset exactly expectedOldCount times, no changes will be made.
        Specified by:
        setCount in interface Multiset<E>
        Parameters:
        element - the element to conditionally set the count of; may be null only if explicitly allowed by the implementation
        expectedOldCount - the expected present count of the element in this multiset
        newCount - the desired count of the element in this multiset
        Returns:
        true if the change was successful. This usually indicates that the multiset has been modified, but not always: in the case that expectedOldCount == newCount, the method will return true if the condition was met.
        Throws:
        java.lang.IllegalArgumentException - if expectedOldCount or newCount is negative

      • entrySet

        public java.util.Set<Multiset.Entry<E>> entrySet()
        Description copied from interface: Multiset
        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 Multiset.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.

        Specified by:
        entrySet in interface Multiset<E>
        Returns:
        a set of entries representing the data of this multiset

      • isEmpty

        public boolean isEmpty()
        Specified by:
        isEmpty in interface java.util.Collection<E>

      • clear

        public void clear()
        Specified by:
        clear in interface java.util.Collection<E>

      • contains

        public boolean contains​(@Nullable
                        java.lang.Object element)
        Description copied from interface: Multiset
        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 java.util.Collection<E>
        Specified by:
        contains in interface Multiset<E>
        Overrides:
        contains in class java.util.AbstractCollection<E>
        Parameters:
        element - the element to check for
        Returns:
        true if this multiset contains at least one occurrence of the element

      • iterator

        public java.util.Iterator<E> iterator()
        Description copied from interface: Multiset

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

        Specified by:
        iterator in interface java.util.Collection<E>
        Specified by:
        iterator in interface java.lang.Iterable<E>
        Specified by:
        iterator in interface Multiset<E>
        Specified by:
        iterator in class java.util.AbstractCollection<E>

      • add

        public boolean add​(@Nullable
                   E element)
        Description copied from interface: Multiset
        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 java.util.Collection<E>
        Specified by:
        add in interface Multiset<E>
        Overrides:
        add in class java.util.AbstractCollection<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

      • remove

        public boolean remove​(@Nullable
                      java.lang.Object element)
        Description copied from interface: Multiset
        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 java.util.Collection<E>
        Specified by:
        remove in interface Multiset<E>
        Overrides:
        remove in class java.util.AbstractCollection<E>
        Parameters:
        element - the element to remove one occurrence of
        Returns:
        true if an occurrence was found and removed

      • addAll

        public boolean addAll​(java.util.Collection<? extends E> elementsToAdd)

        This implementation is highly efficient when elementsToAdd is itself a Multiset.

        Specified by:
        addAll in interface java.util.Collection<E>
        Overrides:
        addAll in class java.util.AbstractCollection<E>

      • removeAll

        public boolean removeAll​(java.util.Collection<?> elementsToRemove)
        Description copied from interface: Multiset

        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 java.util.Collection<E>
        Specified by:
        removeAll in interface Multiset<E>
        Overrides:
        removeAll in class java.util.AbstractCollection<E>

      • retainAll

        public boolean retainAll​(java.util.Collection<?> elementsToRetain)
        Description copied from interface: Multiset

        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 java.util.Collection<E>
        Specified by:
        retainAll in interface Multiset<E>
        Overrides:
        retainAll in class java.util.AbstractCollection<E>
        See Also:
        Multisets.retainOccurrences(Multiset, Multiset)

      • elementSet

        public java.util.Set<E> elementSet()
        Description copied from interface: Multiset
        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().

        Specified by:
        elementSet in interface Multiset<E>
        Returns:
        a view of the set of distinct elements in this multiset

      • equals

        public boolean equals​(@Nullable
                      java.lang.Object object)
        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.

        This implementation returns true if object is a multiset of the same size and if, for each element, the two multisets have the same count.

        Specified by:
        equals in interface java.util.Collection<E>
        Specified by:
        equals in interface Multiset<E>
        Overrides:
        equals in class java.lang.Object

      • hashCode

        public int hashCode()
        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.

        This implementation returns the hash code of Multiset.entrySet().

        Specified by:
        hashCode in interface java.util.Collection<E>
        Specified by:
        hashCode in interface Multiset<E>
        Overrides:
        hashCode in class java.lang.Object

      • toString

        public java.lang.String toString()

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

        This implementation returns the result of invoking toString on Multiset.entrySet().

        Specified by:
        toString in interface Multiset<E>
        Overrides:
        toString in class java.util.AbstractCollection<E>