Package com.google.common.collect

Class ForwardingMultiset<E>

  • All Implemented Interfaces:
    Multiset<E>, java.lang.Iterable<E>, java.util.Collection<E>
    Direct Known Subclasses:
    ForwardingSortedMultiset, ForwardingSortedMultiset.StandardDescendingMultiset
    @GwtCompatible
public abstract class ForwardingMultiset<E>
extends ForwardingCollection<E>
implements Multiset<E>
    A multiset which forwards all its method calls to another multiset. Subclasses should override one or more methods to modify the behavior of the backing multiset as desired per the decorator pattern.

    Warning: The methods of ForwardingMultiset forward indiscriminately to the methods of the delegate. For example, overriding add(Object, int) alone will not change the behavior of ForwardingCollection.add(Object), which can lead to unexpected behavior. In this case, you should override add(Object) as well, either providing your own implementation, or delegating to the provided standardAdd method.

    The standard methods and any collection views they return are not guaranteed to be thread-safe, even when all of the methods that they depend on are thread-safe.

    Since:
    2.0 (imported from Google Collections Library)

    • Constructor Detail

      • ForwardingMultiset

        protected ForwardingMultiset()
        Constructor for use by subclasses.

    • Method Detail

      • delegate

        protected abstract Multiset<E> delegate()
        Description copied from class: ForwardingObject
        Returns the backing delegate instance that methods are forwarded to. Abstract subclasses generally override this method with an abstract method that has a more specific return type, such as ForwardingSet.delegate(). Concrete subclasses override this method to supply the instance being decorated.
        Specified by:
        delegate in class ForwardingCollection<E>

      • count

        public int count​(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​(E element,
               int occurrences)
        Description copied from interface: Multiset
        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

      • remove

        public int remove​(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

      • 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

      • 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

      • equals

        public boolean equals​(@Nullable
                      java.lang.Object object)
        Description copied from interface: Multiset
        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 java.util.Collection<E>
        Specified by:
        equals in interface Multiset<E>
        Overrides:
        equals in class java.lang.Object

      • hashCode

        public int hashCode()
        Description copied from interface: Multiset
        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 java.util.Collection<E>
        Specified by:
        hashCode in interface Multiset<E>
        Overrides:
        hashCode in class java.lang.Object

      • setCount

        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>
        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

      • setCount

        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>
        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.

      • standardHashCode

        protected int standardHashCode()
        A sensible definition of hashCode() as entrySet().hashCode() . If you override entrySet(), you may wish to override hashCode() to forward to this implementation.
        Since:
        7.0