edu.emory.mathcs.backport.java.util.concurrent

Class ConcurrentSkipListMap

public class ConcurrentSkipListMap extends AbstractMap implements ConcurrentNavigableMap, Cloneable, Serializable

A scalable concurrent ConcurrentNavigableMap implementation. The map is sorted according to the Comparable natural ordering of its keys, or by a Comparator provided at map creation time, depending on which constructor is used.

This class implements a concurrent variant of SkipLists providing expected average log(n) time cost for the containsKey, get, put and remove operations and their variants. Insertion, removal, update, and access operations safely execute concurrently by multiple threads. Iterators are weakly consistent, returning elements reflecting the state of the map at some point at or since the creation of the iterator. They do not throw java.util.ConcurrentModificationException, and may proceed concurrently with other operations. Ascending key ordered views and their iterators are faster than descending ones.

All Map.Entry pairs returned by methods in this class and its views represent snapshots of mappings at the time they were produced. They do not support the Entry.setValue method. (Note however that it is possible to change mappings in the associated map using put, putIfAbsent, or replace, depending on exactly which effect you need.)

Beware that, unlike in most collections, the size method is not a constant-time operation. Because of the asynchronous nature of these maps, determining the current number of elements requires a traversal of the elements. Additionally, the bulk operations putAll, equals, and clear are not guaranteed to be performed atomically. For example, an iterator operating concurrently with a putAll operation might view only some of the added elements.

This class and its views and iterators implement all of the optional methods of the Map and Iterator interfaces. Like most other concurrent collections, this class does not permit the use of null keys or values because some null return values cannot be reliably distinguished from the absence of elements.

This class is a member of the Java Collections Framework.

Since: 1.6

Author: Doug Lea

Constructor Summary
ConcurrentSkipListMap()
Constructs a new, empty map, sorted according to the Comparable natural ordering of the keys.
ConcurrentSkipListMap(Comparator comparator)
Constructs a new, empty map, sorted according to the specified comparator.
ConcurrentSkipListMap(Map m)
Constructs a new map containing the same mappings as the given map, sorted according to the Comparable natural ordering of the keys.
ConcurrentSkipListMap(SortedMap m)
Constructs a new map containing the same mappings and using the same ordering as the specified sorted map.
Method Summary
EntryceilingEntry(Object key)
Returns a key-value mapping associated with the least key greater than or equal to the given key, or null if there is no such entry.
ObjectceilingKey(Object key)
voidclear()
Removes all of the mappings from this map.
Objectclone()
Returns a shallow copy of this ConcurrentSkipListMap instance.
Comparatorcomparator()
booleancontainsKey(Object key)
Returns true if this map contains a mapping for the specified key.
booleancontainsValue(Object value)
Returns true if this map maps one or more keys to the specified value.
NavigableSetdescendingKeySet()
NavigableMapdescendingMap()
SetentrySet()
Returns a Set view of the mappings contained in this map.
booleanequals(Object o)
Compares the specified object with this map for equality.
EntryfirstEntry()
Returns a key-value mapping associated with the least key in this map, or null if the map is empty.
ObjectfirstKey()
EntryfloorEntry(Object key)
Returns a key-value mapping associated with the greatest key less than or equal to the given key, or null if there is no such key.
ObjectfloorKey(Object key)
Objectget(Object key)
Returns the value to which the specified key is mapped, or {@code null} if this map contains no mapping for the key.
NavigableMapheadMap(Object toKey, boolean inclusive)
SortedMapheadMap(Object toKey)
EntryhigherEntry(Object key)
Returns a key-value mapping associated with the least key strictly greater than the given key, or null if there is no such key.
ObjecthigherKey(Object key)
booleanisEmpty()
Returns true if this map contains no key-value mappings.
SetkeySet()
Returns a NavigableSet view of the keys contained in this map.
EntrylastEntry()
Returns a key-value mapping associated with the greatest key in this map, or null if the map is empty.
ObjectlastKey()
EntrylowerEntry(Object key)
Returns a key-value mapping associated with the greatest key strictly less than the given key, or null if there is no such key.
ObjectlowerKey(Object key)
NavigableSetnavigableKeySet()
EntrypollFirstEntry()
Removes and returns a key-value mapping associated with the least key in this map, or null if the map is empty.
EntrypollLastEntry()
Removes and returns a key-value mapping associated with the greatest key in this map, or null if the map is empty.
Objectput(Object key, Object value)
Associates the specified value with the specified key in this map.
ObjectputIfAbsent(Object key, Object value)
{@inheritDoc }
Objectremove(Object key)
Removes the mapping for the specified key from this map if present.
booleanremove(Object key, Object value)
{@inheritDoc }
booleanreplace(Object key, Object oldValue, Object newValue)
{@inheritDoc }
Objectreplace(Object key, Object value)
{@inheritDoc }
intsize()
Returns the number of key-value mappings in this map.
NavigableMapsubMap(Object fromKey, boolean fromInclusive, Object toKey, boolean toInclusive)
SortedMapsubMap(Object fromKey, Object toKey)
NavigableMaptailMap(Object fromKey, boolean inclusive)
SortedMaptailMap(Object fromKey)
Collectionvalues()
Returns a Collection view of the values contained in this map.

Constructor Detail

ConcurrentSkipListMap

public ConcurrentSkipListMap()
Constructs a new, empty map, sorted according to the Comparable natural ordering of the keys.

ConcurrentSkipListMap

public ConcurrentSkipListMap(Comparator comparator)
Constructs a new, empty map, sorted according to the specified comparator.

Parameters: comparator the comparator that will be used to order this map. If null, the Comparable natural ordering of the keys will be used.

ConcurrentSkipListMap

public ConcurrentSkipListMap(Map m)
Constructs a new map containing the same mappings as the given map, sorted according to the Comparable natural ordering of the keys.

Parameters: m the map whose mappings are to be placed in this map

Throws: ClassCastException if the keys in m are not Comparable, or are not mutually comparable NullPointerException if the specified map or any of its keys or values are null

ConcurrentSkipListMap

public ConcurrentSkipListMap(SortedMap m)
Constructs a new map containing the same mappings and using the same ordering as the specified sorted map.

Parameters: m the sorted map whose mappings are to be placed in this map, and whose comparator is to be used to sort this map

Throws: NullPointerException if the specified sorted map or any of its keys or values are null

Method Detail

ceilingEntry

public Entry ceilingEntry(Object key)
Returns a key-value mapping associated with the least key greater than or equal to the given key, or null if there is no such entry. The returned entry does not support the Entry.setValue method.

Throws: ClassCastException {@inheritDoc } NullPointerException if the specified key is null

ceilingKey

public Object ceilingKey(Object key)

Throws: ClassCastException {@inheritDoc } NullPointerException if the specified key is null

clear

public void clear()
Removes all of the mappings from this map.

clone

public Object clone()
Returns a shallow copy of this ConcurrentSkipListMap instance. (The keys and values themselves are not cloned.)

Returns: a shallow copy of this map

comparator

public Comparator comparator()

containsKey

public boolean containsKey(Object key)
Returns true if this map contains a mapping for the specified key.

Parameters: key key whose presence in this map is to be tested

Returns: true if this map contains a mapping for the specified key

Throws: ClassCastException if the specified key cannot be compared with the keys currently in the map NullPointerException if the specified key is null

containsValue

public boolean containsValue(Object value)
Returns true if this map maps one or more keys to the specified value. This operation requires time linear in the map size.

Parameters: value value whose presence in this map is to be tested

Returns: true if a mapping to value exists; false otherwise

Throws: NullPointerException if the specified value is null

descendingKeySet

public NavigableSet descendingKeySet()

descendingMap

public NavigableMap descendingMap()

entrySet

public Set entrySet()
Returns a Set view of the mappings contained in this map. The set's iterator returns the entries in ascending key order. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

The view's iterator is a "weakly consistent" iterator that will never throw java.util.ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

The Map.Entry elements returned by iterator.next() do not support the setValue operation.

Returns: a set view of the mappings contained in this map, sorted in ascending key order

equals

public boolean equals(Object o)
Compares the specified object with this map for equality. Returns true if the given object is also a map and the two maps represent the same mappings. More formally, two maps m1 and m2 represent the same mappings if m1.entrySet().equals(m2.entrySet()). This operation may return misleading results if either map is concurrently modified during execution of this method.

Parameters: o object to be compared for equality with this map

Returns: true if the specified object is equal to this map

firstEntry

public Entry firstEntry()
Returns a key-value mapping associated with the least key in this map, or null if the map is empty. The returned entry does not support the Entry.setValue method.

firstKey

public Object firstKey()

Throws: NoSuchElementException {@inheritDoc }

floorEntry

public Entry floorEntry(Object key)
Returns a key-value mapping associated with the greatest key less than or equal to the given key, or null if there is no such key. The returned entry does not support the Entry.setValue method.

Parameters: key the key

Throws: ClassCastException {@inheritDoc } NullPointerException if the specified key is null

floorKey

public Object floorKey(Object key)

Parameters: key the key

Throws: ClassCastException {@inheritDoc } NullPointerException if the specified key is null

get

public Object get(Object key)
Returns the value to which the specified key is mapped, or {@code null} if this map contains no mapping for the key.

More formally, if this map contains a mapping from a key {@code k} to a value {@code v} such that {@code key} compares equal to {@code k} according to the map's ordering, then this method returns {@code v}; otherwise it returns {@code null}. (There can be at most one such mapping.)

Throws: ClassCastException if the specified key cannot be compared with the keys currently in the map NullPointerException if the specified key is null

headMap

public NavigableMap headMap(Object toKey, boolean inclusive)

Throws: ClassCastException {@inheritDoc } NullPointerException if {@code toKey} is null IllegalArgumentException {@inheritDoc }

headMap

public SortedMap headMap(Object toKey)

Throws: ClassCastException {@inheritDoc } NullPointerException if {@code toKey} is null IllegalArgumentException {@inheritDoc }

higherEntry

public Entry higherEntry(Object key)
Returns a key-value mapping associated with the least key strictly greater than the given key, or null if there is no such key. The returned entry does not support the Entry.setValue method.

Parameters: key the key

Throws: ClassCastException {@inheritDoc } NullPointerException if the specified key is null

higherKey

public Object higherKey(Object key)

Parameters: key the key

Throws: ClassCastException {@inheritDoc } NullPointerException if the specified key is null

isEmpty

public boolean isEmpty()
Returns true if this map contains no key-value mappings.

Returns: true if this map contains no key-value mappings

keySet

public Set keySet()
Returns a NavigableSet view of the keys contained in this map. The set's iterator returns the keys in ascending order. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. The set supports element removal, which removes the corresponding mapping from the map, via the {@code Iterator.remove}, {@code Set.remove}, {@code removeAll}, {@code retainAll}, and {@code clear} operations. It does not support the {@code add} or {@code addAll} operations.

The view's {@code iterator} is a "weakly consistent" iterator that will never throw java.util.ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

This method is equivalent to method {@code navigableKeySet}.

Returns: a navigable set view of the keys in this map

lastEntry

public Entry lastEntry()
Returns a key-value mapping associated with the greatest key in this map, or null if the map is empty. The returned entry does not support the Entry.setValue method.

lastKey

public Object lastKey()

Throws: NoSuchElementException {@inheritDoc }

lowerEntry

public Entry lowerEntry(Object key)
Returns a key-value mapping associated with the greatest key strictly less than the given key, or null if there is no such key. The returned entry does not support the Entry.setValue method.

Throws: ClassCastException {@inheritDoc } NullPointerException if the specified key is null

lowerKey

public Object lowerKey(Object key)

Throws: ClassCastException {@inheritDoc } NullPointerException if the specified key is null

navigableKeySet

public NavigableSet navigableKeySet()

pollFirstEntry

public Entry pollFirstEntry()
Removes and returns a key-value mapping associated with the least key in this map, or null if the map is empty. The returned entry does not support the Entry.setValue method.

pollLastEntry

public Entry pollLastEntry()
Removes and returns a key-value mapping associated with the greatest key in this map, or null if the map is empty. The returned entry does not support the Entry.setValue method.

put

public Object put(Object key, Object value)
Associates the specified value with the specified key in this map. If the map previously contained a mapping for the key, the old value is replaced.

Parameters: key key with which the specified value is to be associated value value to be associated with the specified key

Returns: the previous value associated with the specified key, or null if there was no mapping for the key

Throws: ClassCastException if the specified key cannot be compared with the keys currently in the map NullPointerException if the specified key or value is null

putIfAbsent

public Object putIfAbsent(Object key, Object value)
{@inheritDoc }

Returns: the previous value associated with the specified key, or null if there was no mapping for the key

Throws: ClassCastException if the specified key cannot be compared with the keys currently in the map NullPointerException if the specified key or value is null

remove

public Object remove(Object key)
Removes the mapping for the specified key from this map if present.

Parameters: key key for which mapping should be removed

Returns: the previous value associated with the specified key, or null if there was no mapping for the key

Throws: ClassCastException if the specified key cannot be compared with the keys currently in the map NullPointerException if the specified key is null

remove

public boolean remove(Object key, Object value)
{@inheritDoc }

Throws: ClassCastException if the specified key cannot be compared with the keys currently in the map NullPointerException if the specified key is null

replace

public boolean replace(Object key, Object oldValue, Object newValue)
{@inheritDoc }

Throws: ClassCastException if the specified key cannot be compared with the keys currently in the map NullPointerException if any of the arguments are null

replace

public Object replace(Object key, Object value)
{@inheritDoc }

Returns: the previous value associated with the specified key, or null if there was no mapping for the key

Throws: ClassCastException if the specified key cannot be compared with the keys currently in the map NullPointerException if the specified key or value is null

size

public int size()
Returns the number of key-value mappings in this map. If this map contains more than Integer.MAX_VALUE elements, it returns Integer.MAX_VALUE.

Beware that, unlike in most collections, this method is NOT a constant-time operation. Because of the asynchronous nature of these maps, determining the current number of elements requires traversing them all to count them. Additionally, it is possible for the size to change during execution of this method, in which case the returned result will be inaccurate. Thus, this method is typically not very useful in concurrent applications.

Returns: the number of elements in this map

subMap

public NavigableMap subMap(Object fromKey, boolean fromInclusive, Object toKey, boolean toInclusive)

Throws: ClassCastException {@inheritDoc } NullPointerException if {@code fromKey} or {@code toKey} is null IllegalArgumentException {@inheritDoc }

subMap

public SortedMap subMap(Object fromKey, Object toKey)

Throws: ClassCastException {@inheritDoc } NullPointerException if {@code fromKey} or {@code toKey} is null IllegalArgumentException {@inheritDoc }

tailMap

public NavigableMap tailMap(Object fromKey, boolean inclusive)

Throws: ClassCastException {@inheritDoc } NullPointerException if {@code fromKey} is null IllegalArgumentException {@inheritDoc }

tailMap

public SortedMap tailMap(Object fromKey)

Throws: ClassCastException {@inheritDoc } NullPointerException if {@code fromKey} is null IllegalArgumentException {@inheritDoc }

values

public Collection values()
Returns a Collection view of the values contained in this map. The collection's iterator returns the values in ascending order of the corresponding keys. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. The collection supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

The view's iterator is a "weakly consistent" iterator that will never throw java.util.ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.