Class ForwardingMultiset<E extends @Nullable Object>
- java.lang.Object
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- com.google.common.collect.ForwardingObject
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- com.google.common.collect.ForwardingCollection<E>
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- com.google.common.collect.ForwardingMultiset<E>
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- All Implemented Interfaces:
Multiset<E>
,Iterable<E>
,Collection<E>
- Direct Known Subclasses:
ForwardingSortedMultiset
,ForwardingSortedMultiset.StandardDescendingMultiset
@GwtCompatible public abstract class ForwardingMultiset<E extends @Nullable Object> 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, overridingadd(Object, int)
alone will not change the behavior ofForwardingCollection.add(Object)
, which can lead to unexpected behavior. In this case, you should overrideadd(Object)
as well, either providing your own implementation, or delegating to the providedstandardAdd
method.default
method warning: This class does not forward calls todefault
methods. Instead, it inherits their default implementations. When those implementations invoke methods, they invoke methods on theForwardingMultiset
.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
- Author:
- Kevin Bourrillion, Louis Wasserman
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Nested Class Summary
Nested Classes Modifier and Type Class Description protected class
ForwardingMultiset.StandardElementSet
A sensible implementation ofMultiset.elementSet()
in terms of the following methods:ForwardingCollection.clear()
,ForwardingCollection.contains(java.lang.Object)
,ForwardingCollection.containsAll(java.util.Collection<?>)
,count(java.lang.Object)
,ForwardingCollection.isEmpty()
, theSet.size()
andSet.iterator()
methods ofentrySet()
, andremove(Object, int)
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Nested classes/interfaces inherited from interface com.google.common.collect.Multiset
Multiset.Entry<E extends @Nullable Object>
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Constructor Summary
Constructors Modifier Constructor Description protected
ForwardingMultiset()
Constructor for use by subclasses.
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Method Summary
All Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description int
add(E element, int occurrences)
Adds a number of occurrences of an element to this multiset.int
count(Object element)
Returns the number of occurrences of an element in this multiset (the count of the element).protected abstract Multiset<E>
delegate()
Returns the backing delegate instance that methods are forwarded to.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 intoMultiset.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.int
remove(Object element, int occurrences)
Removes a number of occurrences of the specified element from this multiset.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 inMultiset.setCount(Object, int)
, provided that the element has the expected current count.protected boolean
standardAdd(E element)
A sensible definition ofForwardingCollection.add(Object)
in terms ofadd(Object, int)
.protected boolean
standardAddAll(Collection<? extends E> elementsToAdd)
A sensible definition ofForwardingCollection.addAll(Collection)
in terms ofForwardingCollection.add(Object)
andadd(Object, int)
.protected void
standardClear()
A sensible definition ofForwardingCollection.clear()
in terms of theiterator
method ofentrySet()
.protected boolean
standardContains(Object object)
A sensible definition ofForwardingCollection.contains(java.lang.Object)
in terms ofcount(java.lang.Object)
.protected int
standardCount(Object object)
A sensible, albeit inefficient, definition ofcount(java.lang.Object)
in terms ofentrySet()
.protected boolean
standardEquals(Object object)
A sensible, albeit inefficient, definition ofequals(java.lang.Object)
in terms ofentrySet().size()
andcount(java.lang.Object)
.protected int
standardHashCode()
A sensible definition ofhashCode()
asentrySet().hashCode()
.protected Iterator<E>
standardIterator()
A sensible definition ofForwardingCollection.iterator()
in terms ofentrySet()
andForwardingCollection.remove(Object)
.protected boolean
standardRemove(Object element)
A sensible definition ofForwardingCollection.remove(Object)
in terms ofremove(Object, int)
.protected boolean
standardRemoveAll(Collection<?> elementsToRemove)
A sensible definition ofForwardingCollection.removeAll(java.util.Collection<?>)
in terms of theremoveAll
method ofelementSet()
.protected boolean
standardRetainAll(Collection<?> elementsToRetain)
A sensible definition ofForwardingCollection.retainAll(java.util.Collection<?>)
in terms of theretainAll
method ofelementSet()
.protected int
standardSetCount(E element, int count)
A sensible definition ofsetCount(Object, int)
in terms ofcount(Object)
,add(Object, int)
, andremove(Object, int)
.protected boolean
standardSetCount(E element, int oldCount, int newCount)
A sensible definition ofsetCount(Object, int, int)
in terms ofcount(Object)
andsetCount(Object, int)
.protected int
standardSize()
A sensible, albeit inefficient, definition ofForwardingCollection.size()
in terms ofentrySet()
.protected String
standardToString()
A sensible definition ofForwardingObject.toString()
asentrySet().toString()
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Methods inherited from class com.google.common.collect.ForwardingCollection
add, addAll, clear, contains, containsAll, isEmpty, iterator, remove, removeAll, retainAll, size, standardContainsAll, standardIsEmpty, standardToArray, standardToArray, toArray, toArray
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Methods inherited from class com.google.common.collect.ForwardingObject
toString
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Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
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Methods inherited from interface java.util.Collection
addAll, clear, isEmpty, parallelStream, removeIf, spliterator, stream, toArray, toArray, toArray
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Constructor Detail
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ForwardingMultiset
protected ForwardingMultiset()
Constructor for use by subclasses.
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Method Detail
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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 asForwardingSet.delegate()
. Concrete subclasses override this method to supply the instance being decorated.- Specified by:
delegate
in classForwardingCollection<E extends @Nullable Object>
-
count
public int count(@CheckForNull 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 anObject.equals(java.lang.Object)
-based multiset, this gives the same result asCollections.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.
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add
@CanIgnoreReturnValue 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 ifoccurrences == 1
, this method has the identical effect toMultiset.add(Object)
. This method is functionally equivalent (except in the case of overflow) to the calladdAll(Collections.nCopies(element, occurrences))
, which would presumably perform much more poorly.- Specified by:
add
in interfaceMultiset<E extends @Nullable Object>
- Parameters:
element
- the element to add occurrences of; may be null only if explicitly allowed by the implementationoccurrences
- 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
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remove
@CanIgnoreReturnValue public int remove(@CheckForNull 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 ifoccurrences == 1
, this is functionally equivalent to the callremove(element)
.- Specified by:
remove
in interfaceMultiset<E extends @Nullable Object>
- Parameters:
element
- the element to conditionally remove occurrences ofoccurrences
- 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
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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 interfaceMultiset<E extends @Nullable Object>
- Returns:
- a view of the set of distinct elements in this multiset
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entrySet
public Set<Multiset.Entry<E>> entrySet()
Description copied from interface:Multiset
Returns a view of the contents of this multiset, grouped intoMultiset.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 theMultiset.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 theEntry
instances themselves don't even have methods for modification. See the specific implementation class for more details on how its entry set handles modifications.
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equals
public boolean equals(@CheckForNull Object object)
Description copied from class:java.lang.Object
Indicates whether some other object is "equal to" this one.The
equals
method implements an equivalence relation on non-null object references:- It is reflexive: for any non-null reference value
x
,x.equals(x)
should returntrue
. - It is symmetric: for any non-null reference values
x
andy
,x.equals(y)
should returntrue
if and only ify.equals(x)
returnstrue
. - It is transitive: for any non-null reference values
x
,y
, andz
, ifx.equals(y)
returnstrue
andy.equals(z)
returnstrue
, thenx.equals(z)
should returntrue
. - It is consistent: for any non-null reference values
x
andy
, multiple invocations ofx.equals(y)
consistently returntrue
or consistently returnfalse
, provided no information used inequals
comparisons on the objects is modified. - For any non-null reference value
x
,x.equals(null)
should returnfalse
.
The
equals
method for classObject
implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference valuesx
andy
, this method returnstrue
if and only ifx
andy
refer to the same object (x == y
has the valuetrue
).Note that it is generally necessary to override the
hashCode
method whenever this method is overridden, so as to maintain the general contract for thehashCode
method, which states that equal objects must have equal hash codes.- Specified by:
equals
in interfaceCollection<E extends @Nullable Object>
- Specified by:
equals
in interfaceMultiset<E extends @Nullable Object>
- Overrides:
equals
in classObject
- Parameters:
object
- the reference object with which to compare.- Returns:
true
if this object is the same as the obj argument;false
otherwise.- See Also:
Object.hashCode()
,HashMap
- It is reflexive: for any non-null reference value
-
hashCode
public int hashCode()
Description copied from class:java.lang.Object
Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided byHashMap
.The general contract of
hashCode
is:- Whenever it is invoked on the same object more than once during
an execution of a Java application, the
hashCode
method must consistently return the same integer, provided no information used inequals
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. - If two objects are equal according to the
equals(Object)
method, then calling thehashCode
method on each of the two objects must produce the same integer result. - It is not required that if two objects are unequal
according to the
Object.equals(java.lang.Object)
method, then calling thehashCode
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. (The hashCode may or may not be implemented as some function of an object's memory address at some point in time.)- Specified by:
hashCode
in interfaceCollection<E extends @Nullable Object>
- Specified by:
hashCode
in interfaceMultiset<E extends @Nullable Object>
- Overrides:
hashCode
in classObject
- Returns:
- a hash code value for this object.
- See Also:
Object.equals(java.lang.Object)
,System.identityHashCode(java.lang.Object)
- Whenever it is invoked on the same object more than once during
an execution of a Java application, the
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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 interfaceMultiset<E extends @Nullable Object>
- Parameters:
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 multiset- Returns:
- the count of the element before the operation; possibly zero
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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 inMultiset.setCount(Object, int)
, provided that the element has the expected current count. If the current count is notoldCount
, no change is made.- Specified by:
setCount
in interfaceMultiset<E extends @Nullable Object>
- Parameters:
element
- the element to conditionally set the count of; may be null only if explicitly allowed by the implementationoldCount
- the expected present count of the element in this multisetnewCount
- 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, unlessoldCount == newCount
.
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standardContains
protected boolean standardContains(@CheckForNull Object object)
A sensible definition ofForwardingCollection.contains(java.lang.Object)
in terms ofcount(java.lang.Object)
. If you overridecount(java.lang.Object)
, you may wish to overrideForwardingCollection.contains(java.lang.Object)
to forward to this implementation.- Overrides:
standardContains
in classForwardingCollection<E extends @Nullable Object>
- Since:
- 7.0
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standardClear
protected void standardClear()
A sensible definition ofForwardingCollection.clear()
in terms of theiterator
method ofentrySet()
. If you overrideentrySet()
, you may wish to overrideForwardingCollection.clear()
to forward to this implementation.- Overrides:
standardClear
in classForwardingCollection<E extends @Nullable Object>
- Since:
- 7.0
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standardCount
@Beta protected int standardCount(@CheckForNull Object object)
A sensible, albeit inefficient, definition ofcount(java.lang.Object)
in terms ofentrySet()
. If you overrideentrySet()
, you may wish to overridecount(java.lang.Object)
to forward to this implementation.- Since:
- 7.0
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standardAdd
protected boolean standardAdd(E element)
A sensible definition ofForwardingCollection.add(Object)
in terms ofadd(Object, int)
. If you overrideadd(Object, int)
, you may wish to overrideForwardingCollection.add(Object)
to forward to this implementation.- Since:
- 7.0
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standardAddAll
@Beta protected boolean standardAddAll(Collection<? extends E> elementsToAdd)
A sensible definition ofForwardingCollection.addAll(Collection)
in terms ofForwardingCollection.add(Object)
andadd(Object, int)
. If you override either of these methods, you may wish to overrideForwardingCollection.addAll(Collection)
to forward to this implementation.- Overrides:
standardAddAll
in classForwardingCollection<E extends @Nullable Object>
- Since:
- 7.0
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standardRemove
protected boolean standardRemove(@CheckForNull Object element)
A sensible definition ofForwardingCollection.remove(Object)
in terms ofremove(Object, int)
. If you overrideremove(Object, int)
, you may wish to overrideForwardingCollection.remove(Object)
to forward to this implementation.- Overrides:
standardRemove
in classForwardingCollection<E extends @Nullable Object>
- Since:
- 7.0
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standardRemoveAll
protected boolean standardRemoveAll(Collection<?> elementsToRemove)
A sensible definition ofForwardingCollection.removeAll(java.util.Collection<?>)
in terms of theremoveAll
method ofelementSet()
. If you overrideelementSet()
, you may wish to overrideForwardingCollection.removeAll(java.util.Collection<?>)
to forward to this implementation.- Overrides:
standardRemoveAll
in classForwardingCollection<E extends @Nullable Object>
- Since:
- 7.0
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standardRetainAll
protected boolean standardRetainAll(Collection<?> elementsToRetain)
A sensible definition ofForwardingCollection.retainAll(java.util.Collection<?>)
in terms of theretainAll
method ofelementSet()
. If you overrideelementSet()
, you may wish to overrideForwardingCollection.retainAll(java.util.Collection<?>)
to forward to this implementation.- Overrides:
standardRetainAll
in classForwardingCollection<E extends @Nullable Object>
- Since:
- 7.0
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standardSetCount
protected int standardSetCount(E element, int count)
A sensible definition ofsetCount(Object, int)
in terms ofcount(Object)
,add(Object, int)
, andremove(Object, int)
.entrySet()
. If you override any of these methods, you may wish to overridesetCount(Object, int)
to forward to this implementation.- Since:
- 7.0
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standardSetCount
protected boolean standardSetCount(E element, int oldCount, int newCount)
A sensible definition ofsetCount(Object, int, int)
in terms ofcount(Object)
andsetCount(Object, int)
. If you override either of these methods, you may wish to overridesetCount(Object, int, int)
to forward to this implementation.- Since:
- 7.0
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standardIterator
protected Iterator<E> standardIterator()
A sensible definition ofForwardingCollection.iterator()
in terms ofentrySet()
andForwardingCollection.remove(Object)
. If you override either of these methods, you may wish to overrideForwardingCollection.iterator()
to forward to this implementation.- Since:
- 7.0
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standardSize
protected int standardSize()
A sensible, albeit inefficient, definition ofForwardingCollection.size()
in terms ofentrySet()
. If you overrideentrySet()
, you may wish to overrideForwardingCollection.size()
to forward to this implementation.- Since:
- 7.0
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standardEquals
protected boolean standardEquals(@CheckForNull Object object)
A sensible, albeit inefficient, definition ofequals(java.lang.Object)
in terms ofentrySet().size()
andcount(java.lang.Object)
. If you override either of these methods, you may wish to overrideequals(java.lang.Object)
to forward to this implementation.- Since:
- 7.0
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standardHashCode
protected int standardHashCode()
A sensible definition ofhashCode()
asentrySet().hashCode()
. If you overrideentrySet()
, you may wish to overridehashCode()
to forward to this implementation.- Since:
- 7.0
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standardToString
protected String standardToString()
A sensible definition ofForwardingObject.toString()
asentrySet().toString()
. If you overrideentrySet()
, you may wish to overrideForwardingObject.toString()
to forward to this implementation.- Overrides:
standardToString
in classForwardingCollection<E extends @Nullable Object>
- Since:
- 7.0
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