com.google.common.collect
Class ConcurrentHashMultiset<E>

java.lang.Object
  extended by java.util.AbstractCollection<E>
      extended by com.google.common.collect.ConcurrentHashMultiset<E>
All Implemented Interfaces:
Multiset<E>, Serializable, Iterable<E>, Collection<E>

public final class ConcurrentHashMultiset<E>
extends AbstractCollection<E>
implements Serializable

A multiset that supports concurrent modifications and that provides atomic versions of most Multiset operations (exceptions where noted). Null elements are not supported.

Author:
Cliff L. Biffle
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)
          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.
 boolean containsAll(Collection<?> elements)
          Returns true if this collection contains all of the elements in the specified collection.
 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.
 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 oldCount, int newCount)
          Sets the number of occurrences of element to newCount, but only if the count is currently oldCount.
 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.
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
 

Method Detail

create

public static <E> ConcurrentHashMultiset<E> create()
Creates a new, empty ConcurrentHashMultiset using the default initial capacity, load factor, and concurrency settings.


create

public 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.

Parameters:
elements - the elements that the multiset should contain

count

public int count(@Nullable
                 Object element)
Returns the number of occurrences of element in this multiset.

Specified by:
count in interface Multiset<E>
Parameters:
element - the element to look for
Returns:
the nonnegative number of occurrences of the element

size

public int size()
Returns the number of elements in this collection. If this collection contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

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.

Specified by:
size in interface Collection<E>
Returns:
the number of elements in this collection

toArray

public Object[] toArray()
Description copied from class: java.util.AbstractCollection
Returns an array containing all of the elements in this collection. 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.

The 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();
 

Specified by:
toArray in interface Collection<E>
Overrides:
toArray in class AbstractCollection<E>
Returns:
an array containing all of the elements in this collection

toArray

public <T> T[] toArray(T[] array)
Description copied from class: java.util.AbstractCollection
Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. If the collection fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this collection.

If 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);
 

Specified by:
toArray in interface Collection<E>
Overrides:
toArray in class AbstractCollection<E>
Parameters:
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.
Returns:
an array containing all of the elements in this collection

add

public int add(E element,
               int occurrences)
Adds a number of occurrences of the specified element to this multiset.

Specified by:
add in interface Multiset<E>
Parameters:
element - the element to add
occurrences - the number of occurrences to add
Returns:
the previous count of the element before the operation; possibly zero
Throws:
IllegalArgumentException - if occurrences is negative, or if the resulting amount would exceed Integer.MAX_VALUE

remove

public int remove(@Nullable
                  Object element,
                  int occurrences)
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.

Specified by:
remove in interface Multiset<E>
Parameters:
element - the element whose occurrences should be removed
occurrences - the number of occurrences of the element to remove
Returns:
the count of the element before the operation; possibly zero
Throws:
IllegalArgumentException - if occurrences is negative

removeExactly

public boolean removeExactly(@Nullable
                             Object element,
                             int occurrences)
Removes exactly the specified number of occurrences of 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.

Parameters:
element - the element to remove
occurrences - the number of occurrences of element to remove
Returns:
true if the removal was possible (including if occurrences is zero)

setCount

public int setCount(E element,
                    int count)
Adds or removes occurrences of element such that the count(java.lang.Object) of the element becomes 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 element in the multiset before this call
Throws:
IllegalArgumentException - if count is negative

setCount

public boolean setCount(E element,
                        int oldCount,
                        int newCount)
Sets the number of occurrences of element to newCount, but only if the count is currently oldCount. If element does not appear in the multiset exactly oldCount times, no changes will be 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 change was successful. This usually indicates that the multiset has been modified, but not always: in the case that oldCount == newCount, the method will return true if the condition was met.
Throws:
IllegalArgumentException - if oldCount or newCount is negative

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

isEmpty

public boolean isEmpty()
Description copied from class: java.util.AbstractCollection
Returns true if this collection contains no elements.

This implementation returns size() == 0.

Specified by:
isEmpty in interface Collection<E>
Overrides:
isEmpty in class AbstractCollection<E>
Returns:
true if this collection contains no elements

contains

public boolean contains(@Nullable
                        Object element)
Description copied from class: java.util.AbstractCollection
Returns true if this collection contains the specified element. More formally, returns true if and only if this collection contains at least one element e such that (o==null ? e==null : o.equals(e)).

This implementation iterates over the elements in the collection, checking each element in turn for equality with the specified element.

Specified by:
contains in interface Multiset<E>
Specified by:
contains in interface Collection<E>
Overrides:
contains in class AbstractCollection<E>
Parameters:
element - element whose presence in this collection is to be tested
Returns:
true if this collection contains the specified element

iterator

public Iterator<E> iterator()
Description copied from class: java.util.AbstractCollection
Returns an iterator over the elements contained in this collection.

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>
Returns:
an iterator over the elements contained in this collection

add

public boolean add(@Nullable
                   E element)
Description copied from class: java.util.AbstractCollection
Ensures that this collection contains the specified element (optional operation). Returns true if this collection changed as a result of the call. (Returns false if this collection does not permit duplicates and already contains the specified element.)

Collections 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.

Specified by:
add in interface Multiset<E>
Specified by:
add in interface Collection<E>
Overrides:
add in class AbstractCollection<E>
Parameters:
element - element whose presence in this collection is to be ensured
Returns:
true if this collection changed as a result of the call

remove

public boolean remove(Object element)
Description copied from class: java.util.AbstractCollection
Removes a single instance of the specified element from this collection, if it is present (optional operation). More formally, removes an element e such that (o==null ? e==null : o.equals(e)), if this collection contains one or more such elements. Returns true if this collection contained the specified element (or equivalently, if this collection changed as a result of the call).

This 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.

Specified by:
remove in interface Multiset<E>
Specified by:
remove in interface Collection<E>
Overrides:
remove in class AbstractCollection<E>
Parameters:
element - element to be removed from this collection, if present
Returns:
true if an element was removed as a result of this call

containsAll

public boolean containsAll(Collection<?> elements)
Description copied from class: java.util.AbstractCollection
Returns true if this collection contains all of the elements in the specified collection.

This implementation iterates over the specified collection, checking each element returned by the iterator in turn to see if it's contained in this collection. If all elements are so contained true is returned, otherwise false.

Specified by:
containsAll in interface Multiset<E>
Specified by:
containsAll in interface Collection<E>
Overrides:
containsAll in class AbstractCollection<E>
Parameters:
elements - collection to be checked for containment in this collection
Returns:
true if this collection contains all of the elements in the specified collection
See Also:
AbstractCollection.contains(Object)

addAll

public boolean addAll(Collection<? extends E> elementsToAdd)
Description copied from class: java.util.AbstractCollection
Adds all of the elements in the specified collection to this collection (optional operation). The behavior of this operation is undefined if the specified collection is modified while the operation is in progress. (This implies that the behavior of this call is undefined if the specified collection is this collection, and this collection is nonempty.)

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).

Specified by:
addAll in interface Collection<E>
Overrides:
addAll in class AbstractCollection<E>
Parameters:
elementsToAdd - collection containing elements to be added to this collection
Returns:
true if this collection changed as a result of the call
See Also:
AbstractCollection.add(Object)

removeAll

public boolean removeAll(Collection<?> elementsToRemove)
Description copied from class: java.util.AbstractCollection
Removes all of this collection's elements that are also contained in the specified collection (optional operation). After this call returns, this collection will contain no elements in common with the specified collection.

This 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.

Specified by:
removeAll in interface Multiset<E>
Specified by:
removeAll in interface Collection<E>
Overrides:
removeAll in class AbstractCollection<E>
Parameters:
elementsToRemove - collection containing elements to be removed from this collection
Returns:
true if this collection changed as a result of the call
See Also:
AbstractCollection.remove(Object), AbstractCollection.contains(Object)

retainAll

public boolean retainAll(Collection<?> elementsToRetain)
Description copied from class: java.util.AbstractCollection
Retains only the elements in this collection that are contained in the specified collection (optional operation). In other words, removes from this collection all of its elements that are not contained in the specified collection.

This 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.

Specified by:
retainAll in interface Multiset<E>
Specified by:
retainAll in interface Collection<E>
Overrides:
retainAll in class AbstractCollection<E>
Parameters:
elementsToRetain - collection containing elements to be retained in this collection
Returns:
true if this collection changed as a result of the call
See Also:
AbstractCollection.remove(Object), AbstractCollection.contains(Object)

clear

public void clear()
Description copied from class: java.util.AbstractCollection
Removes all of the elements from this collection (optional operation). The collection will be empty after this method returns.

This 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.

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

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>
Returns:
a view of the set of distinct elements in this multiset

equals

public boolean equals(@Nullable
                      Object object)
Indicates whether some other object is "equal to" this one.

The equals method implements an equivalence relation on non-null object references:

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 other 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
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(), Hashtable

hashCode

public int hashCode()
Returns a hash code value for the object. This method is supported for the benefit of hashtables such as those provided by java.util.Hashtable.

The general contract of hashCode is:

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().

Specified by:
hashCode in interface Multiset<E>
Specified by:
hashCode in interface Collection<E>
Overrides:
hashCode in class Object
Returns:
a hash code value for this object.
See Also:
Object.equals(java.lang.Object), Hashtable

toString

public String toString()
Returns a string representation of this collection. The string representation consists of a list of the collection's elements in the order they are returned by its iterator, enclosed in square brackets ("[]"). Adjacent elements are separated by the characters ", " (comma and space). Elements are converted to strings as by String.valueOf(Object).

This implementation returns the result of invoking toString on Multiset.entrySet().

Specified by:
toString in interface Multiset<E>
Overrides:
toString in class AbstractCollection<E>
Returns:
a string representation of this collection