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## com.google.common.collect
Class TreeMultiset<E>

    java.lang.Object
      java.util.AbstractCollection<E>
          com.google.common.collect.TreeMultiset<E>

All Implemented Interfaces:
  Multiset<E>, SortedMultiset<E>, Serializable, Iterable<E>, Collection<E>

    @GwtCompatible(emulated=true)
    public final class TreeMultiset<E>

extends AbstractCollection<E>
implements Serializable

A multiset which maintains the ordering of its elements, according to either their natural order or an explicit `Comparator`. In all cases, this implementation uses `Comparable.compareTo(T)` or `Comparator.compare(T, T)` instead of `Object.equals(java.lang.Object)` to determine equivalence of instances.

Warning: The comparison must be consistent with equals as explained by the `Comparable` class specification. Otherwise, the resulting multiset will violate the `Collection` contract, which is specified in terms of `Object.equals(java.lang.Object)`.

See the Guava User Guide article on `Multiset`.

Since:
  2.0 (imported from Google Collections Library)
Author:
  Louis Wasserman, Jared Levy
See Also:
  Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface com.google.common.collect.Multiset
`Multiset.Entry<E>`

Method Summary
`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(Collection<? extends E> elementsToAdd)`
`void` | `clear()`
`Comparator<? super E>` | `comparator()` Returns the comparator that orders this multiset, or `Ordering.natural()` if the natural ordering of the elements is used.
`boolean` | `contains(Object element)` Determines whether this multiset contains the specified element.
`int` | `count(Object element)` Returns the number of occurrences of an element in this multiset (the count of the element).
`static
`<E extends Comparable> TreeMultiset<E>`
` | `create()` Creates a new, empty multiset, sorted according to the elements' natural order.
`static
`<E> TreeMultiset<E>`
` | `create(Comparator<? super E> comparator)` Creates a new, empty multiset, sorted according to the specified comparator.
`static
`<E extends Comparable> TreeMultiset<E>`
` | `create(Iterable<? extends E> elements)` Creates an empty multiset containing the given initial elements, sorted according to the elements' natural order.
`SortedMultiset<E>` | `descendingMultiset()` Returns a descending view of this multiset.
`SortedSet<E>` | `elementSet()` Returns the set of distinct elements contained in this multiset.
`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(Object object)` Compares the specified object with this multiset for equality.
`Multiset.Entry<E>` | `firstEntry()` Returns the entry of the first element in this multiset, or `null` if this multiset is empty.
`int` | `hashCode()` Returns the hash code for this multiset.
`SortedMultiset<E>` | `headMultiset(E upperBound, BoundType boundType)` Returns a view of this multiset restricted to the elements less than `upperBound`, optionally including `upperBound` itself.
`boolean` | `isEmpty()`
`Iterator<E>` | `iterator()`
`Multiset.Entry<E>` | `lastEntry()` Returns the entry of the last element in this multiset, or `null` if this multiset is empty.
`Multiset.Entry<E>` | `pollFirstEntry()` Returns and removes the entry associated with the lowest element in this multiset, or returns `null` if this multiset is empty.
`Multiset.Entry<E>` | `pollLastEntry()` Returns and removes the entry associated with the greatest element in this multiset, or returns `null` if this multiset is empty.
`boolean` | `remove(Object element)` Removes a single occurrence of the specified element from this multiset, if present.
`int` | `remove(Object element, int occurrences)` Removes a number of occurrences of the specified element from this multiset.
`boolean` | `removeAll(Collection<?> elementsToRemove)`
`boolean` | `retainAll(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()`
`SortedMultiset<E>` | `subMultiset(E fromElement, BoundType fromBoundType, E toElement, BoundType toBoundType)` Returns a view of this multiset restricted to the range between `lowerBound` and `upperBound`.
`SortedMultiset<E>` | `tailMultiset(E lowerBound, BoundType boundType)` Returns a view of this multiset restricted to the elements greater than `lowerBound`, optionally including `lowerBound` itself.
`String` | `toString()`

Methods inherited from class java.util.AbstractCollection
`containsAll, toArray, toArray`

Methods inherited from class java.lang.Object
`clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

Methods inherited from interface com.google.common.collect.SortedMultiset
`iterator`

Methods inherited from interface com.google.common.collect.Multiset
`add, contains, containsAll, entrySet, equals, hashCode, remove, removeAll, retainAll, toString`

Methods inherited from interface java.util.Collection
`addAll, clear, isEmpty, toArray, toArray`

Method Detail

### create

    public static <E extends Comparable> TreeMultiset<E> create()

  Creates a new, empty multiset, sorted according to the elements' natural order. All elements inserted into the multiset must implement the `Comparable` interface. Furthermore, all such elements must be mutually comparable: `e1.compareTo(e2)` must not throw a `ClassCastException` for any elements `e1` and `e2` in the multiset. If the user attempts to add an element to the multiset that violates this constraint (for example, the user attempts to add a string element to a set whose elements are integers), the `add(Object)` call will throw a `ClassCastException`.

  The type specification is `<E extends Comparable>`, instead of the more specific `<E extends Comparable<? super E>>`, to support classes defined without generics.

### create

    public static <E> TreeMultiset<E> create(@Nullable
                                             Comparator<? super E> comparator)

  Creates a new, empty multiset, sorted according to the specified comparator. All elements inserted into the multiset must be mutually comparable by the specified comparator: `comparator.compare(e1, e2)` must not throw a `ClassCastException` for any elements `e1` and `e2` in the multiset. If the user attempts to add an element to the multiset that violates this constraint, the `add(Object)` call will throw a `ClassCastException`.

  Parameters:
    `comparator` - the comparator that will be used to sort this multiset. A null value indicates that the elements' natural ordering should be used.

### create

    public static <E extends Comparable> TreeMultiset<E> create(Iterable<? extends E> elements)

  Creates an empty multiset containing the given initial elements, sorted according to the elements' natural order.

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

  The type specification is `<E extends Comparable>`, instead of the more specific `<E extends Comparable<? super E>>`, to support classes defined without generics.

### size

    public int size()

  Specified by:
    `size` in interface `Collection<E>`

### 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>`
  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)

  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(@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>`
  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

### 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`.

### headMultiset

    public SortedMultiset<E> headMultiset(@Nullable
                                          E upperBound,
                                          BoundType boundType)

  Description copied from interface: `SortedMultiset`
  Returns a view of this multiset restricted to the elements less than `upperBound`, optionally including `upperBound` itself. The returned multiset is a view of this multiset, so changes to one will be reflected in the other. The returned multiset supports all operations that this multiset supports.

  The returned multiset will throw an `IllegalArgumentException` on attempts to add elements outside its range.

  Specified by:
    `headMultiset` in interface `SortedMultiset<E>`

### tailMultiset

    public SortedMultiset<E> tailMultiset(@Nullable
                                          E lowerBound,
                                          BoundType boundType)

  Description copied from interface: `SortedMultiset`
  Returns a view of this multiset restricted to the elements greater than `lowerBound`, optionally including `lowerBound` itself. The returned multiset is a view of this multiset, so changes to one will be reflected in the other. The returned multiset supports all operations that this multiset supports.

  The returned multiset will throw an `IllegalArgumentException` on attempts to add elements outside its range.

  Specified by:
    `tailMultiset` in interface `SortedMultiset<E>`

### elementSet

    public SortedSet<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>`
  Specified by:
    `elementSet` in interface `SortedMultiset<E>`
  Returns:
    a view of the set of distinct elements in this multiset

### comparator

    public Comparator<? super E> comparator()

  Description copied from interface: `SortedMultiset`
  Returns the comparator that orders this multiset, or `Ordering.natural()` if the natural ordering of the elements is used.

  Specified by:
    `comparator` in interface `SortedMultiset<E>`

### firstEntry

    public Multiset.Entry<E> firstEntry()

  Description copied from interface: `SortedMultiset`
  Returns the entry of the first element in this multiset, or `null` if this multiset is empty.

  Specified by:
    `firstEntry` in interface `SortedMultiset<E>`

### lastEntry

    public Multiset.Entry<E> lastEntry()

  Description copied from interface: `SortedMultiset`
  Returns the entry of the last element in this multiset, or `null` if this multiset is empty.

  Specified by:
    `lastEntry` in interface `SortedMultiset<E>`

### pollFirstEntry

    public Multiset.Entry<E> pollFirstEntry()

  Description copied from interface: `SortedMultiset`
  Returns and removes the entry associated with the lowest element in this multiset, or returns `null` if this multiset is empty.

  Specified by:
    `pollFirstEntry` in interface `SortedMultiset<E>`

### pollLastEntry

    public Multiset.Entry<E> pollLastEntry()

  Description copied from interface: `SortedMultiset`
  Returns and removes the entry associated with the greatest element in this multiset, or returns `null` if this multiset is empty.

  Specified by:
    `pollLastEntry` in interface `SortedMultiset<E>`

### subMultiset

    public SortedMultiset<E> subMultiset(@Nullable
                                         E fromElement,
                                         BoundType fromBoundType,
                                         @Nullable
                                         E toElement,
                                         BoundType toBoundType)

  Description copied from interface: `SortedMultiset`
  Returns a view of this multiset restricted to the range between `lowerBound` and `upperBound`. The returned multiset is a view of this multiset, so changes to one will be reflected in the other. The returned multiset supports all operations that this multiset supports.

  The returned multiset will throw an `IllegalArgumentException` on attempts to add elements outside its range.

  This method is equivalent to `tailMultiset(lowerBound, lowerBoundType).headMultiset(upperBound, upperBoundType)`.

  Specified by:
    `subMultiset` in interface `SortedMultiset<E>`

### descendingMultiset

    public SortedMultiset<E> descendingMultiset()

  Description copied from interface: `SortedMultiset`
  Returns a descending view of this multiset. Modifications made to either map will be reflected in the other.

  Specified by:
    `descendingMultiset` in interface `SortedMultiset<E>`

### isEmpty

    public boolean isEmpty()

  Specified by:
    `isEmpty` in interface `Collection<E>`
  Overrides:
    `isEmpty` in class `AbstractCollection<E>`

### 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 `Multiset<E>`
  Specified by:
    `contains` in interface `Collection<E>`
  Overrides:
    `contains` in class `AbstractCollection<E>`
  Parameters:
    `element` - the element to check for
  Returns:
    `true` if this multiset contains at least one occurrence of the element

### 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 `Multiset<E>`
  Specified by:
    `iterator` in interface `Iterable<E>`
  Specified by:
    `iterator` in interface `Collection<E>`
  Specified by:
    `iterator` in class `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 `Multiset<E>`
  Specified by:
    `add` in interface `Collection<E>`
  Overrides:
    `add` in class `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
                          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 `Multiset<E>`
  Specified by:
    `remove` in interface `Collection<E>`
  Overrides:
    `remove` in class `AbstractCollection<E>`
  Parameters:
    `element` - the element to remove one occurrence of
  Returns:
    `true` if an occurrence was found and removed

### addAll

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

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

  Specified by:
    `addAll` in interface `Collection<E>`
  Overrides:
    `addAll` in class `AbstractCollection<E>`

### removeAll

    public 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 `Multiset<E>`
  Specified by:
    `removeAll` in interface `Collection<E>`
  Overrides:
    `removeAll` in class `AbstractCollection<E>`

### retainAll

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

### clear

    public void clear()

  Specified by:
    `clear` in interface `Collection<E>`
  Overrides:
    `clear` in class `AbstractCollection<E>`

### entrySet

    public 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
                          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 `Multiset<E>`
  Specified by:
    `equals` in interface `Collection<E>`
  Overrides:
    `equals` in class `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 `Multiset<E>`
  Specified by:
    `hashCode` in interface `Collection<E>`
  Overrides:
    `hashCode` in class `Object`

### toString

    public 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 `AbstractCollection<E>`

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