Package com.google.common.collect

Class HashMultiset<E>

  • All Implemented Interfaces:
    Multiset<E>, java.io.Serializable, java.lang.Iterable<E>, java.util.Collection<E>
    @GwtCompatible(serializable=true,
               emulated=true)
public final class HashMultiset<E>
extends java.util.AbstractCollection<E>
    Multiset implementation backed by a HashMap.
    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 an 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 an element in this multiset (the count of the element).
      static <E> HashMultiset<E> create()
      Creates a new, empty HashMultiset using the default initial capacity.
      static <E> HashMultiset<E> create​(int distinctElements)
      Creates a new, empty HashMultiset with the specified expected number of distinct elements.
      static <E> HashMultiset<E> create​(java.lang.Iterable<? extends E> elements)
      Creates a new HashMultiset containing the specified elements.
      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 retainAll​(java.util.Collection<?> elementsToRetain)
      int setCount​(E element, int count)
      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)
      Conditionally sets the count of an element to a new value, as described in Multiset.setCount(Object, int), provided that the element has the expected current count.
      int size()  
      java.lang.String toString()

      • Methods inherited from class java.util.AbstractCollection

        containsAll, toArray, toArray

      • 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, toArray, toArray

      • Methods inherited from interface java.lang.Iterable

        forEach

    • Method Detail

      • create

        public static <E> HashMultiset<E> create()
        Creates a new, empty HashMultiset using the default initial capacity.

      • create

        public static <E> HashMultiset<E> create​(int distinctElements)
        Creates a new, empty HashMultiset with the specified expected number of distinct elements.
        Parameters:
        distinctElements - the expected number of distinct elements
        Throws:
        java.lang.IllegalArgumentException - if distinctElements is negative

      • create

        public static <E> HashMultiset<E> create​(java.lang.Iterable<? extends E> elements)
        Creates a new HashMultiset containing the specified elements.

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

        Parameters:
        elements - the elements that the multiset should contain

      • entrySet

        public 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. 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.

        Invoking Multiset.Entry.getCount() on an entry in the returned set always returns the current count of that element in the multiset, as opposed to the count at the time the entry was retrieved.

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

      • clear

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

      • size

        public int size()
        Specified by:
        size in interface java.util.Collection<E>

      • 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>

      • count

        public int count​(@Nullable
                 java.lang.Object element)
        Description copied from interface: Multiset
        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(java.lang.Iterable<?>, java.lang.Object) generalizes this operation; it correctly delegates to this method when dealing with a multiset, but it can also accept any other iterable type.

        Specified by:
        count in interface Multiset<E>
        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

        public int add​(@Nullable
               E element,
               int occurrences)
        Adds a number of occurrences of an element to this multiset. Note that if occurrences == 1, this method has the identical effect to Multiset.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.
        Specified by:
        add in interface Multiset<E>
        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:
        java.lang.IllegalArgumentException - if the call would result in more than Integer.MAX_VALUE occurrences of element in this multiset.

      • remove

        public int remove​(@Nullable
                  java.lang.Object element,
                  int occurrences)
        Description copied from interface: Multiset
        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).
        Specified by:
        remove in interface Multiset<E>
        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

      • setCount

        public int setCount​(@Nullable
                    E element,
                    int count)
        Description copied from interface: Multiset
        Adds or removes the necessary occurrences of an element such that the element attains the desired 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 the element before the operation; possibly zero

      • isEmpty

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

      • 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

      • setCount

        public boolean setCount​(@Nullable
                        E element,
                        int oldCount,
                        int newCount)
        Description copied from interface: Multiset
        Conditionally sets the count of an element to a new value, as described in Multiset.setCount(Object, int), provided that the element has the expected current count. If the current count is not oldCount, no change is 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
        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.

      • 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>