public final class ConcurrentHashMultiset<E> extends AbstractCollection<E> implements Serializable
Multiset operations (exceptions where noted). Null elements are not supported.
See the Guava User Guide article on
Multiset.
Multiset.Entry<E>| Modifier and Type | Method and Description |
|---|---|
boolean |
add(E element)
Ensures that this collection contains the specified element (optional
operation).
|
int |
add(E element,
int occurrences)
Adds a number of occurrences of the specified element to this multiset.
|
boolean |
addAll(Collection<? extends E> elementsToAdd)
Adds all of the elements in the specified collection to this collection
(optional operation).
|
void |
clear()
Removes all of the elements from this collection (optional operation).
|
boolean |
contains(Object element)
Returns true if this collection contains the specified element.
|
int |
count(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(Iterable<? extends E> elements)
Creates a new
ConcurrentHashMultiset containing the specified elements, 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. |
Set<Multiset.Entry<E>> |
createEntrySet() |
Set<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)
Indicates whether some other object is "equal to" this one.
|
int |
hashCode()
Returns a hash code value for the object.
|
boolean |
isEmpty()
Returns true if this collection contains no elements.
|
Iterator<E> |
iterator()
Returns an iterator over the elements contained in this collection.
|
boolean |
remove(Object element)
Removes a single instance of the specified element from this
collection, if it is present (optional operation).
|
int |
remove(Object element,
int occurrences)
Removes a number of occurrences of the specified element from this multiset.
|
boolean |
removeAll(Collection<?> elementsToRemove)
Removes all of this collection's elements that are also contained in the
specified collection (optional operation).
|
boolean |
removeExactly(Object element,
int occurrences)
Removes exactly the specified number of occurrences of
element, or makes no
change if this is not possible. |
boolean |
retainAll(Collection<?> elementsToRetain)
Retains only the elements in this collection that are contained in the
specified collection (optional operation).
|
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()
Returns the number of elements in this collection.
|
Object[] |
toArray()
Returns an array containing all of the elements in this collection.
|
<T> T[] |
toArray(T[] array)
Returns an array containing all of the elements in this collection;
the runtime type of the returned array is that of the specified array.
|
String |
toString()
Returns a string representation of this collection.
|
containsAllclone, finalize, getClass, notify, notifyAll, wait, wait, waitcontainsAllpublic static <E> ConcurrentHashMultiset<E> create()
ConcurrentHashMultiset using the default
initial capacity, load factor, and concurrency settings.public static <E> ConcurrentHashMultiset<E> create(Iterable<? extends E> elements)
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.
elements - the elements that the multiset should contain@Beta public static <E> ConcurrentHashMultiset<E> create(MapMaker mapMaker)
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.
GenericMapMaker class)
since 7.0)public int count(@Nullable Object element)
element in this multiset.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.
size in interface Collection<E>public Object[] toArray()
java.util.AbstractCollectionThe returned array will be "safe" in that no references to it are maintained by this collection. (In other words, this method must allocate a new array even if this collection is backed by an array). The caller is thus free to modify the returned array.
This method acts as bridge between array-based and collection-based APIs.
This implementation returns an array containing all the elements
returned by this collection's iterator, in the same order, stored in
consecutive elements of the array, starting with index 0.
The length of the returned array is equal to the number of elements
returned by the iterator, even if the size of this collection changes
during iteration, as might happen if the collection permits
concurrent modification during iteration. The size method is
called only as an optimization hint; the correct result is returned
even if the iterator returns a different number of elements.
This method is equivalent to:
List<E> list = new ArrayList<E>(size());
for (E e : this)
list.add(e);
return list.toArray();
toArray in interface Collection<E>toArray in class AbstractCollection<E>public <T> T[] toArray(T[] array)
java.util.AbstractCollectionIf this collection fits in the specified array with room to spare (i.e., the array has more elements than this collection), the element in the array immediately following the end of the collection is set to null. (This is useful in determining the length of this collection only if the caller knows that this collection does not contain any null elements.)
If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.
Like the Collection.toArray() method, this method acts as bridge between
array-based and collection-based APIs. Further, this method allows
precise control over the runtime type of the output array, and may,
under certain circumstances, be used to save allocation costs.
Suppose x is a collection known to contain only strings. The following code can be used to dump the collection into a newly allocated array of String:
String[] y = x.toArray(new String[0]);
Note that toArray(new Object[0]) is identical in function to
toArray().
This implementation returns an array containing all the elements
returned by this collection's iterator in the same order, stored in
consecutive elements of the array, starting with index 0.
If the number of elements returned by the iterator is too large to
fit into the specified array, then the elements are returned in a
newly allocated array with length equal to the number of elements
returned by the iterator, even if the size of this collection
changes during iteration, as might happen if the collection permits
concurrent modification during iteration. The size method is
called only as an optimization hint; the correct result is returned
even if the iterator returns a different number of elements.
This method is equivalent to:
List<E> list = new ArrayList<E>(size());
for (E e : this)
list.add(e);
return list.toArray(a);
toArray in interface Collection<E>toArray in class AbstractCollection<E>array - the array into which the elements of this collection are to be
stored, if it is big enough; otherwise, a new array of the same
runtime type is allocated for this purpose.public int add(E element, int occurrences)
add in interface Multiset<E>element - the element to addoccurrences - the number of occurrences to addIllegalArgumentException - if occurrences is negative, or if
the resulting amount would exceed Integer.MAX_VALUEpublic int remove(@Nullable Object element, int occurrences)
remove in interface Multiset<E>element - the element whose occurrences should be removedoccurrences - the number of occurrences of the element to removeIllegalArgumentException - if occurrences is negativepublic boolean removeExactly(@Nullable Object element, int occurrences)
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.
element - the element to removeoccurrences - the number of occurrences of element to removetrue if the removal was possible (including if occurrences is zero)public int setCount(E element, int count)
element such that the count(java.lang.Object) of the
element becomes count.setCount in interface Multiset<E>element - the element to add or remove occurrences of; may be null
only if explicitly allowed by the implementationcount - the desired count of the element in this multisetelement in the multiset before this callIllegalArgumentException - if count is negativepublic boolean setCount(E element, int expectedOldCount, int newCount)
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.setCount in interface Multiset<E>element - the element to conditionally set the count of; may be null
only if explicitly allowed by the implementationexpectedOldCount - the expected present count of the element in this multisetnewCount - the desired count of the element in this multisettrue 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.IllegalArgumentException - if expectedOldCount or newCount is negativepublic Set<Multiset.Entry<E>> createEntrySet()
public boolean isEmpty()
java.util.AbstractCollectionThis implementation returns size() == 0.
isEmpty in interface Collection<E>public void clear()
java.util.AbstractCollectionThis implementation iterates over this collection, removing each element using the Iterator.remove operation. Most implementations will probably choose to override this method for efficiency.
Note that this implementation will throw an UnsupportedOperationException if the iterator returned by this collection's iterator method does not implement the remove method and this collection is non-empty.
clear in interface Collection<E>public boolean contains(@Nullable Object element)
java.util.AbstractCollectionThis implementation iterates over the elements in the collection, checking each element in turn for equality with the specified element.
contains in interface Multiset<E>contains in interface Collection<E>contains in class AbstractCollection<E>element - element whose presence in this collection is to be testedpublic Iterator<E> iterator()
java.util.AbstractCollectioniterator in interface Multiset<E>iterator in interface Iterable<E>iterator in interface Collection<E>iterator in class AbstractCollection<E>public boolean add(@Nullable E element)
java.util.AbstractCollectionCollections that support this operation may place limitations on what elements may be added to this collection. In particular, some collections will refuse to add null elements, and others will impose restrictions on the type of elements that may be added. Collection classes should clearly specify in their documentation any restrictions on what elements may be added.
If a collection refuses to add a particular element for any reason other than that it already contains the element, it must throw an exception (rather than returning false). This preserves the invariant that a collection always contains the specified element after this call returns.
This implementation always throws an UnsupportedOperationException.
add in interface Multiset<E>add in interface Collection<E>add in class AbstractCollection<E>element - element whose presence in this collection is to be ensuredpublic boolean remove(@Nullable Object element)
java.util.AbstractCollectionThis implementation iterates over the collection looking for the specified element. If it finds the element, it removes the element from the collection using the iterator's remove method.
Note that this implementation throws an UnsupportedOperationException if the iterator returned by this collection's iterator method does not implement the remove method and this collection contains the specified object.
remove in interface Multiset<E>remove in interface Collection<E>remove in class AbstractCollection<E>element - element to be removed from this collection, if presentpublic boolean addAll(Collection<? extends E> elementsToAdd)
This implementation iterates over the specified collection, and adds each object returned by the iterator to this collection, in turn.
Note that this implementation will throw an UnsupportedOperationException unless add is overridden (assuming the specified collection is non-empty).
This implementation is highly efficient when elementsToAdd
is itself a Multiset.
addAll in interface Collection<E>addAll in class AbstractCollection<E>elementsToAdd - collection containing elements to be added to this collectionAbstractCollection.add(Object)public boolean removeAll(Collection<?> elementsToRemove)
java.util.AbstractCollectionThis implementation iterates over this collection, checking each element returned by the iterator in turn to see if it's contained in the specified collection. If it's so contained, it's removed from this collection with the iterator's remove method.
Note that this implementation will throw an UnsupportedOperationException if the iterator returned by the iterator method does not implement the remove method and this collection contains one or more elements in common with the specified collection.
removeAll in interface Multiset<E>removeAll in interface Collection<E>removeAll in class AbstractCollection<E>elementsToRemove - collection containing elements to be removed from this collectionAbstractCollection.remove(Object),
AbstractCollection.contains(Object)public boolean retainAll(Collection<?> elementsToRetain)
java.util.AbstractCollectionThis implementation iterates over this collection, checking each element returned by the iterator in turn to see if it's contained in the specified collection. If it's not so contained, it's removed from this collection with the iterator's remove method.
Note that this implementation will throw an UnsupportedOperationException if the iterator returned by the iterator method does not implement the remove method and this collection contains one or more elements not present in the specified collection.
retainAll in interface Multiset<E>retainAll in interface Collection<E>retainAll in class AbstractCollection<E>elementsToRetain - collection containing elements to be retained in this collectionAbstractCollection.remove(Object),
AbstractCollection.contains(Object)public Set<E> elementSet()
MultisetIf 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().
elementSet in interface Multiset<E>public Set<Multiset.Entry<E>> entrySet()
MultisetMultiset.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.
public boolean equals(@Nullable Object object)
The equals method implements an equivalence relation
on non-null object references:
x, x.equals(x) should return
true.
x and y, x.equals(y)
should return true if and only if
y.equals(x) returns true.
x, y, and z, if
x.equals(y) returns true and
y.equals(z) returns true, then
x.equals(z) should return true.
x and y, multiple invocations of
x.equals(y) consistently return true
or consistently return false, provided no
information used in equals comparisons on the
objects is modified.
x,
x.equals(null) should return false.
The equals method for class Object implements
the most discriminating possible equivalence relation on objects;
that is, for any non-null reference values x and
y, this method returns true if and only
if x and y refer to the same object
(x == y has the value true).
Note that it is generally necessary to override the hashCode
method whenever this method is overridden, so as to maintain the
general contract for the hashCode method, which states
that equal objects must have equal hash codes.
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.
equals in interface Multiset<E>equals in interface Collection<E>equals in class Objectobject - the reference object with which to compare.true if this object is the same as the obj
argument; false otherwise.Object.hashCode(),
HashMappublic int hashCode()
HashMap.
The general contract of hashCode is:
hashCode method
must consistently return the same integer, provided no information
used in equals comparisons on the object is modified.
This integer need not remain consistent from one execution of an
application to another execution of the same application.
equals(Object)
method, then calling the hashCode method on each of
the two objects must produce the same integer result.
Object.equals(java.lang.Object)
method, then calling the hashCode method on each of the
two objects must produce distinct integer results. However, the
programmer should be aware that producing distinct integer results
for unequal objects may improve the performance of hash tables.
As much as is reasonably practical, the hashCode method defined by
class Object does return distinct integers for distinct
objects. (This is typically implemented by converting the internal
address of the object into an integer, but this implementation
technique is not required by the
JavaTM programming language.)
This implementation returns the hash code of Multiset.entrySet().
hashCode in interface Multiset<E>hashCode in interface Collection<E>hashCode in class ObjectObject.equals(java.lang.Object),
System.identityHashCode(java.lang.Object)public String toString()
String.valueOf(Object).
This implementation returns the result of invoking toString on
Multiset.entrySet().
toString in interface Multiset<E>toString in class AbstractCollection<E>Copyright © 2010-2014. All Rights Reserved.