Class HashMultiset<E extends @Nullable Object>

java.lang.Object
java.util.AbstractCollection<E>
com.google.common.collect.HashMultiset<E>
All Implemented Interfaces:
Multiset<E>, Serializable, Iterable<E>, Collection<E>
@GwtCompatible(emulated=true) public final class HashMultiset<E extends @Nullable Object> extends AbstractCollection<E>
Multiset implementation backed by a HashMap.
Since:
2.0
Author:
Kevin Bourrillion, Jared Levy
See Also:

  • Method Details

    • create

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

    • create

      public static <E extends @Nullable Object> 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:
      IllegalArgumentException - if distinctElements is negative

    • create

      public static <E extends @Nullable Object> HashMultiset<E> create(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 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 extends @Nullable Object>
      Returns:
      a set of entries representing the data of this multiset

    • forEachEntry

      public void forEachEntry(ObjIntConsumer<? super E> action)
      Description copied from interface: Multiset
      Runs the specified action for each distinct element in this multiset, and the number of occurrences of that element. For some Multiset implementations, this may be more efficient than iterating over the Multiset.entrySet() either explicitly or with entrySet().forEach(action).
      Specified by:
      forEachEntry in interface Multiset<E extends @Nullable Object>

    • clear

      public void clear()
      Specified by:
      clear in interface Collection<E extends @Nullable Object>

    • size

      public int size()
      Description copied from interface: Multiset
      Returns the total number of all occurrences of all elements in this multiset.

      Note: this method does not return the number of distinct elements in the multiset, which is given by entrySet().size().

      Specified by:
      size in interface Collection<E extends @Nullable Object>
      Specified by:
      size in interface Multiset<E extends @Nullable Object>
      Specified by:
      size in class AbstractCollection<E extends @Nullable Object>

    • iterator

      public 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 Collection<E extends @Nullable Object>
      Specified by:
      iterator in interface Iterable<E extends @Nullable Object>
      Specified by:
      iterator in interface Multiset<E extends @Nullable Object>
      Specified by:
      iterator in class AbstractCollection<E extends @Nullable Object>

    • count

      public int count(@Nullable 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 extends @Nullable Object>
      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

      @CanIgnoreReturnValue public int add(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 extends @Nullable Object>
      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 the call would result in more than Integer.MAX_VALUE occurrences of element in this multiset.

    • remove

      @CanIgnoreReturnValue public int remove(@Nullable 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 extends @Nullable Object>
      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

      @CanIgnoreReturnValue public int setCount(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 extends @Nullable Object>
      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 Collection<E extends @Nullable Object>
      Overrides:
      isEmpty in class AbstractCollection<E extends @Nullable Object>

    • contains

      public boolean contains(@Nullable 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 Collection<E extends @Nullable Object>
      Specified by:
      contains in interface Multiset<E extends @Nullable Object>
      Overrides:
      contains in class AbstractCollection<E extends @Nullable Object>
      Parameters:
      element - the element to check for
      Returns:
      true if this multiset contains at least one occurrence of the element

    • add

      @CanIgnoreReturnValue public final boolean add(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.

      To both add the element and obtain the previous count of that element, use add(element, 1) instead.

      Specified by:
      add in interface Collection<E extends @Nullable Object>
      Specified by:
      add in interface Multiset<E extends @Nullable Object>
      Overrides:
      add in class AbstractCollection<E extends @Nullable Object>
      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

      @CanIgnoreReturnValue public final boolean remove(@Nullable 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.

      To both remove the element and obtain the previous count of that element, use remove(element, 1) instead.

      Specified by:
      remove in interface Collection<E extends @Nullable Object>
      Specified by:
      remove in interface Multiset<E extends @Nullable Object>
      Overrides:
      remove in class AbstractCollection<E extends @Nullable Object>
      Parameters:
      element - the element to remove one occurrence of
      Returns:
      true if an occurrence was found and removed

    • setCount

      @CanIgnoreReturnValue public boolean setCount(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 extends @Nullable Object>
      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

      @CanIgnoreReturnValue public final boolean addAll(Collection<? extends E> elementsToAdd)

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

      Specified by:
      addAll in interface Collection<E extends @Nullable Object>
      Overrides:
      addAll in class AbstractCollection<E extends @Nullable Object>

    • removeAll

      @CanIgnoreReturnValue public final boolean removeAll(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 Collection<E extends @Nullable Object>
      Specified by:
      removeAll in interface Multiset<E extends @Nullable Object>
      Overrides:
      removeAll in class AbstractCollection<E extends @Nullable Object>

    • retainAll

      @CanIgnoreReturnValue public final boolean retainAll(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 Collection<E extends @Nullable Object>
      Specified by:
      retainAll in interface Multiset<E extends @Nullable Object>
      Overrides:
      retainAll in class AbstractCollection<E extends @Nullable Object>
      See Also:

    • elementSet

      public 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 extends @Nullable Object>
      Returns:
      a view of the set of distinct elements in this multiset

    • equals

      public final boolean equals(@Nullable 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 Collection<E extends @Nullable Object>
      Specified by:
      equals in interface Multiset<E extends @Nullable Object>
      Overrides:
      equals in class Object

    • hashCode

      public final 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 Collection<E extends @Nullable Object>
      Specified by:
      hashCode in interface Multiset<E extends @Nullable Object>
      Overrides:
      hashCode in class Object

    • toString

      public final 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 extends @Nullable Object>
      Overrides:
      toString in class AbstractCollection<E extends @Nullable Object>