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java.lang.Objectjava.util.AbstractCollection<E>
com.google.common.collect.AbstractMultiset<E>
public abstract class AbstractMultiset<E>
This class provides a skeletal implementation of the Multiset
interface. A new multiset implementation can be created easily by extending
this class and implementing the Multiset.entrySet()
method, plus
optionally overriding add(Object, int)
and
remove(Object, int)
to enable modifications to the multiset.
The contains(java.lang.Object)
, containsAll(java.util.Collection>)
, count(java.lang.Object)
, and
size()
implementations all iterate across the set returned by
Multiset.entrySet()
, as do many methods acting on the set returned by
elementSet
. Override those methods for better performance.
Nested Class Summary |
---|
Nested classes/interfaces inherited from interface com.google.common.collect.Multiset |
---|
Multiset.Entry<E> |
Constructor Summary | |
---|---|
AbstractMultiset()
|
Method Summary | |
---|---|
boolean |
add(E element)
Adds a single occurrence of the specified element to this multiset. |
boolean |
add(E element,
int occurrences)
Adds a number of occurrences of an element to this multiset. |
boolean |
addAll(Collection<? extends E> elementsToAdd)
|
void |
clear()
|
boolean |
contains(Object element)
Determines whether this multiset contains the specified element. |
boolean |
containsAll(Collection<?> elements)
Returns true if this multiset contains at least one occurrence of
each element in the specified collection. |
int |
count(Object element)
Returns the number of occurrences of an element in this multiset (the count of the element). |
protected Set<E> |
createElementSet()
Creates a new instance of this multiset's element set, which will be returned by elementSet . |
Set<E> |
elementSet()
Returns the set of distinct elements contained in this multiset. |
abstract 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 other)
Compares the specified object with this multiset for equality. |
int |
hashCode()
Returns the hash code for this multiset. |
boolean |
isEmpty()
|
Iterator<E> |
iterator()
|
boolean |
remove(Object element)
Removes a single occurrence of the specified element from this multiset, if present. |
int |
remove(Object element,
int occurrences)
Conditionally removes a number of occurrences of an element from this multiset, provided that at least this many occurrences are present. |
boolean |
removeAll(Collection<?> elementsToRemove)
|
int |
removeAllOccurrences(Object element)
Removes all occurrences of the specified element from this multiset. |
boolean |
retainAll(Collection<?> elementsToRetain)
|
int |
size()
|
String |
toString()
|
Methods inherited from class java.util.AbstractCollection |
---|
toArray, toArray |
Methods inherited from class java.lang.Object |
---|
clone, finalize, getClass, notify, notifyAll, wait, wait, wait |
Methods inherited from interface java.util.Collection |
---|
toArray, toArray |
Constructor Detail |
---|
public AbstractMultiset()
Method Detail |
---|
public abstract Set<Multiset.Entry<E>> entrySet()
Multiset
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.
entrySet
in interface Multiset<E>
public int size()
This implementation iterates across Multiset.entrySet()
and
sums the counts of the entries.
size
in interface Collection<E>
size
in class AbstractCollection<E>
public boolean isEmpty()
isEmpty
in interface Collection<E>
isEmpty
in class AbstractCollection<E>
public boolean contains(@Nullable Object 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.
This implementation checks whether elementSet
contains the
element.
contains
in interface Multiset<E>
contains
in interface Collection<E>
contains
in class AbstractCollection<E>
element
- the element to check for
true
if this multiset contains at least one occurrence of
this elementpublic Iterator<E> iterator()
This implementation usually invokes methods of the
Multiset.entrySet()
iterator. As the only exception, the iterator's
remove
method sometimes calls the multiset's remove
.
iterator
in interface Iterable<E>
iterator
in interface Collection<E>
iterator
in class AbstractCollection<E>
public int count(Object element)
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.
This implementation iterates across Multiset.entrySet()
and
sums the count of all entries.
count
in interface Multiset<E>
element
- the element to count occurrences of
public boolean add(@Nullable E element)
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.
This implementation calls add(Object, int)
with one occurrence.
add
in interface Multiset<E>
add
in interface Collection<E>
add
in class AbstractCollection<E>
element
- the element to add one occurrence of; may be null only if
explicitly allowed by the implementation
true
always, since this call is required to modify the
multiset, unlike other Collection
typespublic boolean add(E element, int occurrences)
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.
This implementation always throws an
UnsupportedOperationException
. To support adding elements, override
it.
add
in interface Multiset<E>
element
- the element to add occurrences of; may be null
only
if explicitly allowed by the implementationoccurrences
- the number of occurrences of this element to add. May
be zero, in which case no change will be made.
public boolean remove(Object element)
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.
This implementation calls remove(Object, int)
with 1
occurrence.
remove
in interface Multiset<E>
remove
in interface Collection<E>
remove
in class AbstractCollection<E>
element
- the element to remove one occurrence of
true
if an occurrence was found and removedpublic int remove(Object element, int occurrences)
occurrences
, no change is made.
Note that if
occurrences == 1
, this is functionally equivalent to the call
remove(element)
.
This implementation always throws an
UnsupportedOperationException
. To support removing elements,
override it.
remove
in interface Multiset<E>
element
- the element to conditionally remove occurrences ofoccurrences
- the number of occurrences of this element to remove. May
be zero, in which case no change will be made.
true
if the condition for modification was met. Unless
occurrences
is zero, this implies that the multiset was indeed
modified.public int removeAllOccurrences(Object element)
Multiset.remove(Object)
, which removes only
one occurrence at a time.
TODO: Nuke this. Use setCount(e, 0).
This implementation calls remove(Object, int)
with
Integer.MAX_VALUE
occurrences.
removeAllOccurrences
in interface Multiset<E>
element
- the element whose occurrences should all be removed
public boolean containsAll(Collection<?> elements)
true
if this multiset contains at least one occurrence of
each element in the specified collection.
This method refines Collection.containsAll(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.
Note: this method does not take into account the occurrence
count of an element in the two collections; it may still return true
even if elements
contains several occurrences of an element
and this multiset contains only one. This is no different than any other
collection type like List
, but it may be unexpected to the user of
a multiset.
This implementation checks whether elementSet
contains the
elements.
containsAll
in interface Multiset<E>
containsAll
in interface Collection<E>
containsAll
in class AbstractCollection<E>
elements
- the collection of elements to be checked for containment in
this multiset
true
if this multiset contains at least one occurrence of
each element contained in elements
public boolean addAll(Collection<? extends E> elementsToAdd)
If the collection being added is a multiset, this implementation
iterates over that multiset's entry set to add the appropriate number of
occurrences of each of its elements to this multiset. Otherwise, it calls
AbstractCollection.addAll(java.util.Collection extends E>)
.
addAll
in interface Collection<E>
addAll
in class AbstractCollection<E>
public boolean removeAll(Collection<?> elementsToRemove)
This method refines Collection.containsAll(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.
This implementation iterates over the elements in the collection and
calls removeAllOccurrences(java.lang.Object)
on each element. In some cases, this
approach has better performance than AbstractCollection.removeAll(java.util.Collection>)
.
removeAll
in interface Multiset<E>
removeAll
in interface Collection<E>
removeAll
in class AbstractCollection<E>
public boolean retainAll(Collection<?> elementsToRetain)
This method refines Collection.containsAll(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.
This implementation iterates over entrySet()
, checking each
entry's element to see if it's contained in the provided collection.
If it's not found, the remove
method of the entry set's
iterator is invoked. In some cases, this approach has better performance
than AbstractCollection.removeAll(java.util.Collection>)
.
retainAll
in interface Multiset<E>
retainAll
in interface Collection<E>
retainAll
in class AbstractCollection<E>
public void clear()
This implementation calls clear
on Multiset.entrySet()
.
clear
in interface Collection<E>
clear
in class AbstractCollection<E>
public Set<E> elementSet()
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()
.
The returned set's methods are implemented by calling
Multiset.entrySet()
methods.
elementSet
in interface Multiset<E>
protected Set<E> createElementSet()
elementSet
.
public boolean equals(@Nullable Object other)
true
if the given object is also a multiset and contains equal
elements with equal counts, regardless of order.
TODO: caveats about equivalence-relation.
This implementation returns true
if other
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 Object
public int hashCode()
(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()
.
hashCode
in interface Multiset<E>
hashCode
in interface Collection<E>
hashCode
in class Object
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, b x 0, e]
This implementation returns the result of invoking toString
on
Multiset.entrySet()
.
toString
in interface Multiset<E>
toString
in class AbstractCollection<E>
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