Class ForwardingMultiset<E extends @Nullable Object>

java.lang.Object

com.google.common.collect.ForwardingObject

com.google.common.collect.ForwardingCollection<E>

com.google.common.collect.ForwardingMultiset<E>

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, 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.

default method warning: This class does not forward calls to default methods. Instead, it inherits their default implementations. When those implementations invoke methods, they invoke methods on the ForwardingMultiset.

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

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
protected class	ForwardingMultiset.StandardElementSet	A sensible implementation of Multiset.elementSet() in terms of the following methods: ForwardingCollection.clear(), ForwardingCollection.contains(Object), ForwardingCollection.containsAll(Collection), count(Object), ForwardingCollection.isEmpty(), the Set.size() and Set.iterator() methods of entrySet(), and remove(Object, int).

Nested classes/interfaces inherited from interface Multiset

Multiset.Entry<E>

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	ForwardingMultiset()	Constructor for use by subclasses.

Method Summary

Modifier and Type	Method	Description
int	add(E element, int occurrences)	Adds a number of occurrences of an element to this multiset.
int	count(@Nullable 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 into Multiset.Entry instances, each providing an element of the multiset and the count of that element.
boolean	equals(@Nullable Object object)	Compares the specified object with this multiset for equality.
int	hashCode()	Returns the hash code for this multiset.
int	remove(@Nullable 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 in Multiset.setCount(Object, int), provided that the element has the expected current count.
protected boolean	standardAdd(E element)	A sensible definition of ForwardingCollection.add(Object) in terms of add(Object, int).
protected boolean	standardAddAll(Collection<? extends E> elementsToAdd)	A sensible definition of ForwardingCollection.addAll(Collection) in terms of ForwardingCollection.add(Object) and add(Object, int).
protected void	standardClear()	A sensible definition of ForwardingCollection.clear() in terms of the iterator method of entrySet().
protected boolean	standardContains(@Nullable Object object)	A sensible definition of ForwardingCollection.contains(Object) in terms of count(Object).
protected int	standardCount(@Nullable Object object)	A sensible, albeit inefficient, definition of count(Object) in terms of entrySet().
protected boolean	standardEquals(@Nullable Object object)	A sensible, albeit inefficient, definition of equals(Object) in terms of entrySet().size() and count(Object).
protected int	standardHashCode()	A sensible definition of hashCode() as entrySet().hashCode() .
protected Iterator<E>	standardIterator()	A sensible definition of ForwardingCollection.iterator() in terms of entrySet() and ForwardingCollection.remove(Object).
protected boolean	standardRemove(@Nullable Object element)	A sensible definition of ForwardingCollection.remove(Object) in terms of remove(Object, int).
protected boolean	standardRemoveAll(Collection<?> elementsToRemove)	A sensible definition of ForwardingCollection.removeAll(Collection) in terms of the removeAll method of elementSet().
protected boolean	standardRetainAll(Collection<?> elementsToRetain)	A sensible definition of ForwardingCollection.retainAll(Collection) in terms of the retainAll method of elementSet().
protected int	standardSetCount(E element, int count)	A sensible definition of setCount(Object, int) in terms of count(Object), add(Object, int), and remove(Object, int).
protected boolean	standardSetCount(E element, int oldCount, int newCount)	A sensible definition of setCount(Object, int, int) in terms of count(Object) and setCount(Object, int).
protected int	standardSize()	A sensible, albeit inefficient, definition of ForwardingCollection.size() in terms of entrySet().
protected String	standardToString()	A sensible definition of ForwardingObject.toString() as entrySet().toString() .

Methods inherited from class ForwardingCollection

add, addAll, clear, contains, containsAll, isEmpty, iterator, remove, removeAll, retainAll, size, standardContainsAll, standardIsEmpty, standardToArray, standardToArray, toArray, toArray

Methods inherited from class ForwardingObject

toString

Methods inherited from class Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface Collection

addAll, clear, isEmpty, parallelStream, removeIf, stream, toArray, toArray, toArray

Methods inherited from interface Multiset

add, contains, containsAll, forEach, forEachEntry, iterator, remove, removeAll, retainAll, size, spliterator, toString

Constructor Details

ForwardingMultiset

protected ForwardingMultiset()

Constructor for use by subclasses.

Method Details

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 extends @Nullable Object>

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(Object)-based multiset, this gives the same result as Collections.frequency(Collection, Object) (which would presumably perform more poorly).

Note: the utility method Iterables.frequency(Iterable, 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 extends @Nullable Object>

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

@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 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 extends @Nullable Object>

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

@CanIgnoreReturnValue
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 extends @Nullable Object>

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 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 extends @Nullable Object>

Returns:

a view of the set of distinct elements in this multiset

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 extends @Nullable Object>

Returns:

a set of entries representing the data of this multiset

equals

public boolean equals(@Nullable 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 Collection<E extends @Nullable Object>

Specified by:

equals in interface Multiset<E extends @Nullable Object>

Overrides:

equals in class 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 Collection<E extends @Nullable Object>

Specified by:

hashCode in interface Multiset<E extends @Nullable Object>

Overrides:

hashCode in class Object

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 interface Multiset<E extends @Nullable Object>

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

@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 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 extends @Nullable Object>

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.

standardContains

protected boolean standardContains(@Nullable Object object)

A sensible definition of ForwardingCollection.contains(Object) in terms of count(Object). If you override count(Object), you may wish to override ForwardingCollection.contains(Object) to forward to this implementation.

Overrides:

standardContains in class ForwardingCollection<E extends @Nullable Object>

Since:

7.0

standardClear

protected void standardClear()

A sensible definition of ForwardingCollection.clear() in terms of the iterator method of entrySet(). If you override entrySet(), you may wish to override ForwardingCollection.clear() to forward to this implementation.

Overrides:

standardClear in class ForwardingCollection<E extends @Nullable Object>

Since:

7.0

standardCount

protected int standardCount(@Nullable Object object)

A sensible, albeit inefficient, definition of count(Object) in terms of entrySet(). If you override entrySet(), you may wish to override count(Object) to forward to this implementation.

Since:

7.0

standardAdd

protected boolean standardAdd(E element)

A sensible definition of ForwardingCollection.add(Object) in terms of add(Object, int). If you override add(Object, int), you may wish to override ForwardingCollection.add(Object) to forward to this implementation.

Since:

7.0

standardAddAll

protected boolean standardAddAll(Collection<? extends E> elementsToAdd)

A sensible definition of ForwardingCollection.addAll(Collection) in terms of ForwardingCollection.add(Object) and add(Object, int). If you override either of these methods, you may wish to override ForwardingCollection.addAll(Collection) to forward to this implementation.

Overrides:

standardAddAll in class ForwardingCollection<E extends @Nullable Object>

Since:

7.0

standardRemove

protected boolean standardRemove(@Nullable Object element)

A sensible definition of ForwardingCollection.remove(Object) in terms of remove(Object, int). If you override remove(Object, int), you may wish to override ForwardingCollection.remove(Object) to forward to this implementation.

Overrides:

standardRemove in class ForwardingCollection<E extends @Nullable Object>

Since:

7.0

standardRemoveAll

protected boolean standardRemoveAll(Collection<?> elementsToRemove)

A sensible definition of ForwardingCollection.removeAll(Collection) in terms of the removeAll method of elementSet(). If you override elementSet(), you may wish to override ForwardingCollection.removeAll(Collection) to forward to this implementation.

Overrides:

standardRemoveAll in class ForwardingCollection<E extends @Nullable Object>

Since:

7.0

standardRetainAll

protected boolean standardRetainAll(Collection<?> elementsToRetain)

A sensible definition of ForwardingCollection.retainAll(Collection) in terms of the retainAll method of elementSet(). If you override elementSet(), you may wish to override ForwardingCollection.retainAll(Collection) to forward to this implementation.

Overrides:

standardRetainAll in class ForwardingCollection<E extends @Nullable Object>

Since:

7.0

standardSetCount

protected int standardSetCount(E element,
 int count)

A sensible definition of setCount(Object, int) in terms of count(Object), add(Object, int), and remove(Object, int). entrySet(). If you override any of these methods, you may wish to override setCount(Object, int) to forward to this implementation.

Since:

7.0

standardSetCount

protected boolean standardSetCount(E element,
 int oldCount,
 int newCount)

A sensible definition of setCount(Object, int, int) in terms of count(Object) and setCount(Object, int). If you override either of these methods, you may wish to override setCount(Object, int, int) to forward to this implementation.

Since:

7.0

standardIterator

protected Iterator<E> standardIterator()

A sensible definition of ForwardingCollection.iterator() in terms of entrySet() and ForwardingCollection.remove(Object). If you override either of these methods, you may wish to override ForwardingCollection.iterator() to forward to this implementation.

Since:

7.0

standardSize

protected int standardSize()

A sensible, albeit inefficient, definition of ForwardingCollection.size() in terms of entrySet(). If you override entrySet(), you may wish to override ForwardingCollection.size() to forward to this implementation.

Since:

7.0

standardEquals

protected boolean standardEquals(@Nullable Object object)

A sensible, albeit inefficient, definition of equals(Object) in terms of entrySet().size() and count(Object). If you override either of these methods, you may wish to override equals(Object) to forward to this implementation.

Since:

7.0

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

standardToString

protected String standardToString()

A sensible definition of ForwardingObject.toString() as entrySet().toString() . If you override entrySet(), you may wish to override ForwardingObject.toString() to forward to this implementation.

Overrides:

standardToString in class ForwardingCollection<E extends @Nullable Object>

Since:

7.0