Java™ Platform

Standard Ed. 6

java.util.concurrent

Class ConcurrentSkipListMap<K,V>

Type Parameters: K - the type of keys maintained by this map V - the type of mapped values

All Implemented Interfaces: Serializable, Cloneable, ConcurrentMap<K,V>, ConcurrentNavigableMap<K,V>, Map<K,V>, NavigableMap<K,V>, SortedMap<K,V>

public class ConcurrentSkipListMap<K,V> extends AbstractMap<K,V> implements ConcurrentNavigableMap<K,V>, Cloneable, Serializable

A scalable concurrent ConcurrentNavigableMap implementation. The map is sorted according to the 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 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 See Also: Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from class java.util.AbstractMap AbstractMap.SimpleEntry<K,V>, AbstractMap.SimpleImmutableEntry<K,V>

Nested classes/interfaces inherited from interface java.util.Map Map.Entry<K,V>

Constructor Summary ConcurrentSkipListMap()

Constructs a new, empty map, sorted according to the natural ordering of the keys. ConcurrentSkipListMap(Comparator<? super K> comparator)

Constructs a new, empty map, sorted according to the specified comparator. ConcurrentSkipListMap(Map<? extends K,? extends V> m)

Constructs a new map containing the same mappings as the given map, sorted according to the natural ordering of the keys. ConcurrentSkipListMap(SortedMap<K,? extends V> m)

Constructs a new map containing the same mappings and using the same ordering as the specified sorted map.

Method Summary Map.Entry<K,V> ceilingEntry(K 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. K ceilingKey(K key)

Returns the least key greater than or equal to the given key, or null if there is no such key. void clear()

Removes all of the mappings from this map. ConcurrentSkipListMap<K,V> clone()

Returns a shallow copy of this ConcurrentSkipListMap instance. Comparator<? super K> comparator()

Returns the comparator used to order the keys in this map, or null if this map uses the natural ordering of its keys. boolean containsKey(Object key)

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

Returns true if this map maps one or more keys to the specified value. NavigableSet<K> descendingKeySet()

Returns a reverse order NavigableSet view of the keys contained in this map. ConcurrentNavigableMap<K,V> descendingMap()

Returns a reverse order view of the mappings contained in this map. Set<Map.Entry<K,V>> entrySet()

Returns a Set view of the mappings contained in this map. boolean equals(Object o)

Compares the specified object with this map for equality. Map.Entry<K,V> firstEntry()

Returns a key-value mapping associated with the least key in this map, or null if the map is empty. K firstKey()

Returns the first (lowest) key currently in this map. Map.Entry<K,V> floorEntry(K 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. K floorKey(K key)

Returns the greatest key less than or equal to the given key, or null if there is no such key. V get(Object key)

Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key. ConcurrentNavigableMap<K,V> headMap(K toKey)

Returns a view of the portion of this map whose keys are strictly less than toKey . ConcurrentNavigableMap<K,V> headMap(K toKey, boolean inclusive)

Returns a view of the portion of this map whose keys are less than (or equal to, if inclusive is true) toKey . Map.Entry<K,V> higherEntry(K 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. K higherKey(K key)

Returns the least key strictly greater than the given key, or null if there is no such key. boolean isEmpty()

Returns true if this map contains no key-value mappings. NavigableSet<K> keySet()

Returns a NavigableSet view of the keys contained in this map. Map.Entry<K,V> lastEntry()

Returns a key-value mapping associated with the greatest key in this map, or null if the map is empty. K lastKey()

Returns the last (highest) key currently in this map. Map.Entry<K,V> lowerEntry(K 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. K lowerKey(K key)

Returns the greatest key strictly less than the given key, or null if there is no such key. NavigableSet<K> navigableKeySet()

Returns a NavigableSet view of the keys contained in this map. Map.Entry<K,V> pollFirstEntry()

Removes and returns a key-value mapping associated with the least key in this map, or null if the map is empty. Map.Entry<K,V> pollLastEntry()

Removes and returns a key-value mapping associated with the greatest key in this map, or null if the map is empty. V put(K key, V value)

Associates the specified value with the specified key in this map. V putIfAbsent(K key, V value)

If the specified key is not already associated with a value, associate it with the given value. V remove(Object key)

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

Removes the entry for a key only if currently mapped to a given value. V replace(K key, V value)

Replaces the entry for a key only if currently mapped to some value. boolean replace(K key, V oldValue, V newValue)

Replaces the entry for a key only if currently mapped to a given value. int size()

Returns the number of key-value mappings in this map. ConcurrentNavigableMap<K,V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive)

Returns a view of the portion of this map whose keys range from fromKey to toKey . ConcurrentNavigableMap<K,V> subMap(K fromKey, K toKey)

Returns a view of the portion of this map whose keys range from fromKey , inclusive, to toKey , exclusive. ConcurrentNavigableMap<K,V> tailMap(K fromKey)

Returns a view of the portion of this map whose keys are greater than or equal to fromKey . ConcurrentNavigableMap<K,V> tailMap(K fromKey, boolean inclusive)

Returns a view of the portion of this map whose keys are greater than (or equal to, if inclusive is true) fromKey . Collection<V> values()

Returns a Collection view of the values contained in this map.

Methods inherited from class java.util.AbstractMap hashCode, putAll, toString

Methods inherited from class java.lang.Object finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Map hashCode, putAll

Constructor Detail

ConcurrentSkipListMap

public ConcurrentSkipListMap()

Constructs a new, empty map, sorted according to the natural ordering of the keys.

ConcurrentSkipListMap

public ConcurrentSkipListMap(Comparator<? super K> 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 natural ordering of the keys will be used.

ConcurrentSkipListMap

public ConcurrentSkipListMap(Map<? extends K,? extends V> m)

Constructs a new map containing the same mappings as the given map, sorted according to the 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<K,? extends V> 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

clone

public ConcurrentSkipListMap<K,V> clone()

Returns a shallow copy of this ConcurrentSkipListMap instance. (The keys and values themselves are not cloned.) Overrides: clone in class AbstractMap<K,V> Returns: a shallow copy of this map See Also: Cloneable

containsKey

public boolean containsKey(Object key)

Returns true if this map contains a mapping for the specified key. Specified by: containsKey in interface Map<K,V> Overrides: containsKey in class AbstractMap<K,V> 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

get

public V get(Object key)

Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key. More formally, if this map contains a mapping from a key k to a value v such that key compares equal to k according to the map's ordering, then this method returns v ; otherwise it returns null . (There can be at most one such mapping.) Specified by: get in interface Map<K,V> Overrides: get in class AbstractMap<K,V> Parameters: key - the key whose associated value is to be returned Returns: the value to which the specified key is mapped, or null if this map contains 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

put

public V put(K key, V 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. Specified by: put in interface Map<K,V> Overrides: put in class AbstractMap<K,V> 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

remove

public V remove(Object key)

Removes the mapping for the specified key from this map if present. Specified by: remove in interface Map<K,V> Overrides: remove in class AbstractMap<K,V> 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

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. Specified by: containsValue in interface Map<K,V> Overrides: containsValue in class AbstractMap<K,V> 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

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. Specified by: size in interface Map<K,V> Overrides: size in class AbstractMap<K,V> Returns: the number of elements in this map

isEmpty

public boolean isEmpty()

Returns true if this map contains no key-value mappings. Specified by: isEmpty in interface Map<K,V> Overrides: isEmpty in class AbstractMap<K,V> Returns: true if this map contains no key-value mappings

clear

public void clear()

Removes all of the mappings from this map. Specified by: clear in interface Map<K,V> Overrides: clear in class AbstractMap<K,V>

keySet

public NavigableSet<K> 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 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 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 navigableKeySet . Specified by: keySet in interface ConcurrentNavigableMap<K,V> Specified by: keySet in interface Map<K,V> Specified by: keySet in interface SortedMap<K,V> Overrides: keySet in class AbstractMap<K,V> Returns: a navigable set view of the keys in this map

navigableKeySet

public NavigableSet<K> navigableKeySet()

Description copied from interface: ConcurrentNavigableMap 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 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 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. Specified by: navigableKeySet in interface ConcurrentNavigableMap<K,V> Specified by: navigableKeySet in interface NavigableMap<K,V> Returns: a navigable set view of the keys in this map

values

public Collection<V> 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 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. Specified by: values in interface Map<K,V> Specified by: values in interface SortedMap<K,V> Overrides: values in class AbstractMap<K,V> Returns: a collection view of the values contained in this map

entrySet

public Set<Map.Entry<K,V>> 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 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. Specified by: entrySet in interface Map<K,V> Specified by: entrySet in interface SortedMap<K,V> Specified by: entrySet in class AbstractMap<K,V> Returns: a set view of the mappings contained in this map, sorted in ascending key order

descendingMap

public ConcurrentNavigableMap<K,V> descendingMap()

Description copied from interface: ConcurrentNavigableMap Returns a reverse order view of the mappings contained in this map. The descending map is backed by this map, so changes to the map are reflected in the descending map, and vice-versa. The returned map has an ordering equivalent to Collections.reverseOrder (comparator()) . The expression m.descendingMap().descendingMap() returns a view of m essentially equivalent to m . Specified by: descendingMap in interface ConcurrentNavigableMap<K,V> Specified by: descendingMap in interface NavigableMap<K,V> Returns: a reverse order view of this map

descendingKeySet

public NavigableSet<K> descendingKeySet()

Description copied from interface: ConcurrentNavigableMap Returns a reverse order NavigableSet view of the keys contained in this map. The set's iterator returns the keys in descending 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 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. Specified by: descendingKeySet in interface ConcurrentNavigableMap<K,V> Specified by: descendingKeySet in interface NavigableMap<K,V> Returns: a reverse order navigable set view of the keys in this map

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. Specified by: equals in interface Map<K,V> Overrides: equals in class AbstractMap<K,V> Parameters: o - object to be compared for equality with this map Returns: true if the specified object is equal to this map See Also: Object.hashCode() , Hashtable

putIfAbsent

public V putIfAbsent(K key, V value)

If the specified key is not already associated with a value, associate it with the given value. This is equivalent to if (!map.containsKey(key)) return map.put(key, value); else return map.get(key); except that the action is performed atomically. Specified by: putIfAbsent in interface ConcurrentMap<K,V> 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

remove

public boolean remove(Object key, Object value)

Removes the entry for a key only if currently mapped to a given value. This is equivalent to if (map.containsKey(key) && map.get(key).equals(value)) { map.remove(key); return true; } else return false; except that the action is performed atomically. Specified by: remove in interface ConcurrentMap<K,V> Parameters: key - key with which the specified value is associated value - value expected to be associated with the specified key Returns: true if the value was removed 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(K key, V oldValue, V newValue)

Replaces the entry for a key only if currently mapped to a given value. This is equivalent to if (map.containsKey(key) && map.get(key).equals(oldValue)) { map.put(key, newValue); return true; } else return false; except that the action is performed atomically. Specified by: replace in interface ConcurrentMap<K,V> Parameters: key - key with which the specified value is associated oldValue - value expected to be associated with the specified key newValue - value to be associated with the specified key Returns: true if the value was replaced 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 V replace(K key, V value)

Replaces the entry for a key only if currently mapped to some value. This is equivalent to if (map.containsKey(key)) { return map.put(key, value); } else return null; except that the action is performed atomically. Specified by: replace in interface ConcurrentMap<K,V> Parameters: key - key with which the specified value is 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

comparator

public Comparator<? super K> comparator()

Description copied from interface: SortedMap Returns the comparator used to order the keys in this map, or null if this map uses the natural ordering of its keys. Specified by: comparator in interface SortedMap<K,V> Returns: the comparator used to order the keys in this map, or null if this map uses the natural ordering of its keys

firstKey

public K firstKey()

Description copied from interface: SortedMap Returns the first (lowest) key currently in this map. Specified by: firstKey in interface SortedMap<K,V> Returns: the first (lowest) key currently in this map Throws: NoSuchElementException - if this map is empty

lastKey

public K lastKey()

Description copied from interface: SortedMap Returns the last (highest) key currently in this map. Specified by: lastKey in interface SortedMap<K,V> Returns: the last (highest) key currently in this map Throws: NoSuchElementException - if this map is empty

subMap

public ConcurrentNavigableMap<K,V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive)

Description copied from interface: NavigableMap Returns a view of the portion of this map whose keys range from fromKey to toKey . If fromKey and toKey are equal, the returned map is empty unless fromExclusive and toExclusive are both true. The returned map is backed by this map, so changes in the returned map are reflected in this map, and vice-versa. The returned map supports all optional map operations that this map supports. The returned map will throw an IllegalArgumentException on an attempt to insert a key outside of its range, or to construct a submap either of whose endpoints lie outside its range. Specified by: subMap in interface ConcurrentNavigableMap<K,V> Specified by: subMap in interface NavigableMap<K,V> Parameters: fromKey - low endpoint of the keys in the returned map fromInclusive - true if the low endpoint is to be included in the returned view toKey - high endpoint of the keys in the returned map toInclusive - true if the high endpoint is to be included in the returned view Returns: a view of the portion of this map whose keys range from fromKey to toKey Throws: ClassCastException - if fromKey and toKey cannot be compared to one another using this map's comparator (or, if the map has no comparator, using natural ordering). Implementations may, but are not required to, throw this exception if fromKey or toKey cannot be compared to keys currently in the map. NullPointerException - if fromKey or toKey is null IllegalArgumentException - if fromKey is greater than toKey ; or if this map itself has a restricted range, and fromKey or toKey lies outside the bounds of the range

headMap

public ConcurrentNavigableMap<K,V> headMap(K toKey, boolean inclusive)

Description copied from interface: NavigableMap Returns a view of the portion of this map whose keys are less than (or equal to, if inclusive is true) toKey . The returned map is backed by this map, so changes in the returned map are reflected in this map, and vice-versa. The returned map supports all optional map operations that this map supports. The returned map will throw an IllegalArgumentException on an attempt to insert a key outside its range. Specified by: headMap in interface ConcurrentNavigableMap<K,V> Specified by: headMap in interface NavigableMap<K,V> Parameters: toKey - high endpoint of the keys in the returned map inclusive - true if the high endpoint is to be included in the returned view Returns: a view of the portion of this map whose keys are less than (or equal to, if inclusive is true) toKey Throws: ClassCastException - if toKey is not compatible with this map's comparator (or, if the map has no comparator, if toKey does not implement Comparable ). Implementations may, but are not required to, throw this exception if toKey cannot be compared to keys currently in the map. NullPointerException - if toKey is null IllegalArgumentException - if this map itself has a restricted range, and toKey lies outside the bounds of the range

tailMap

public ConcurrentNavigableMap<K,V> tailMap(K fromKey, boolean inclusive)

Description copied from interface: NavigableMap Returns a view of the portion of this map whose keys are greater than (or equal to, if inclusive is true) fromKey . The returned map is backed by this map, so changes in the returned map are reflected in this map, and vice-versa. The returned map supports all optional map operations that this map supports. The returned map will throw an IllegalArgumentException on an attempt to insert a key outside its range. Specified by: tailMap in interface ConcurrentNavigableMap<K,V> Specified by: tailMap in interface NavigableMap<K,V> Parameters: fromKey - low endpoint of the keys in the returned map inclusive - true if the low endpoint is to be included in the returned view Returns: a view of the portion of this map whose keys are greater than (or equal to, if inclusive is true) fromKey Throws: ClassCastException - if fromKey is not compatible with this map's comparator (or, if the map has no comparator, if fromKey does not implement Comparable ). Implementations may, but are not required to, throw this exception if fromKey cannot be compared to keys currently in the map. NullPointerException - if fromKey is null IllegalArgumentException - if this map itself has a restricted range, and fromKey lies outside the bounds of the range

subMap

public ConcurrentNavigableMap<K,V> subMap(K fromKey, K toKey)

Description copied from interface: NavigableMap Returns a view of the portion of this map whose keys range from fromKey , inclusive, to toKey , exclusive. (If fromKey and toKey are equal, the returned map is empty.) The returned map is backed by this map, so changes in the returned map are reflected in this map, and vice-versa. The returned map supports all optional map operations that this map supports. The returned map will throw an IllegalArgumentException on an attempt to insert a key outside its range. Equivalent to subMap(fromKey, true, toKey, false) . Specified by: subMap in interface ConcurrentNavigableMap<K,V> Specified by: subMap in interface NavigableMap<K,V> Specified by: subMap in interface SortedMap<K,V> Parameters: fromKey - low endpoint (inclusive) of the keys in the returned map toKey - high endpoint (exclusive) of the keys in the returned map Returns: a view of the portion of this map whose keys range from fromKey , inclusive, to toKey , exclusive Throws: ClassCastException - if fromKey and toKey cannot be compared to one another using this map's comparator (or, if the map has no comparator, using natural ordering). Implementations may, but are not required to, throw this exception if fromKey or toKey cannot be compared to keys currently in the map. NullPointerException - if fromKey or toKey is null IllegalArgumentException - if fromKey is greater than toKey ; or if this map itself has a restricted range, and fromKey or toKey lies outside the bounds of the range

headMap

public ConcurrentNavigableMap<K,V> headMap(K toKey)

Description copied from interface: NavigableMap Returns a view of the portion of this map whose keys are strictly less than toKey . The returned map is backed by this map, so changes in the returned map are reflected in this map, and vice-versa. The returned map supports all optional map operations that this map supports. The returned map will throw an IllegalArgumentException on an attempt to insert a key outside its range. Equivalent to headMap(toKey, false) . Specified by: headMap in interface ConcurrentNavigableMap<K,V> Specified by: headMap in interface NavigableMap<K,V> Specified by: headMap in interface SortedMap<K,V> Parameters: toKey - high endpoint (exclusive) of the keys in the returned map Returns: a view of the portion of this map whose keys are strictly less than toKey Throws: ClassCastException - if toKey is not compatible with this map's comparator (or, if the map has no comparator, if toKey does not implement Comparable ). Implementations may, but are not required to, throw this exception if toKey cannot be compared to keys currently in the map. NullPointerException - if toKey is null IllegalArgumentException - if this map itself has a restricted range, and toKey lies outside the bounds of the range

tailMap

public ConcurrentNavigableMap<K,V> tailMap(K fromKey)

Description copied from interface: NavigableMap Returns a view of the portion of this map whose keys are greater than or equal to fromKey . The returned map is backed by this map, so changes in the returned map are reflected in this map, and vice-versa. The returned map supports all optional map operations that this map supports. The returned map will throw an IllegalArgumentException on an attempt to insert a key outside its range. Equivalent to tailMap(fromKey, true) . Specified by: tailMap in interface ConcurrentNavigableMap<K,V> Specified by: tailMap in interface NavigableMap<K,V> Specified by: tailMap in interface SortedMap<K,V> Parameters: fromKey - low endpoint (inclusive) of the keys in the returned map Returns: a view of the portion of this map whose keys are greater than or equal to fromKey Throws: ClassCastException - if fromKey is not compatible with this map's comparator (or, if the map has no comparator, if fromKey does not implement Comparable ). Implementations may, but are not required to, throw this exception if fromKey cannot be compared to keys currently in the map. NullPointerException - if fromKey is null IllegalArgumentException - if this map itself has a restricted range, and fromKey lies outside the bounds of the range

lowerEntry

public Map.Entry<K,V> lowerEntry(K 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. Specified by: lowerEntry in interface NavigableMap<K,V> Parameters: key - the key Returns: an entry with the greatest key less than key , or null if there is no such key Throws: ClassCastException - if the specified key cannot be compared with the keys currently in the map NullPointerException - if the specified key is null

lowerKey

public K lowerKey(K key)

Description copied from interface: NavigableMap Returns the greatest key strictly less than the given key, or null if there is no such key. Specified by: lowerKey in interface NavigableMap<K,V> Parameters: key - the key Returns: the greatest key less than key , or null if there is no such key Throws: ClassCastException - if the specified key cannot be compared with the keys currently in the map NullPointerException - if the specified key is null

floorEntry

public Map.Entry<K,V> floorEntry(K 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. Specified by: floorEntry in interface NavigableMap<K,V> Parameters: key - the key Returns: an entry with the greatest key less than or equal to key , or null if there is no such key Throws: ClassCastException - if the specified key cannot be compared with the keys currently in the map NullPointerException - if the specified key is null

floorKey

public K floorKey(K key)

Description copied from interface: NavigableMap Returns the greatest key less than or equal to the given key, or null if there is no such key. Specified by: floorKey in interface NavigableMap<K,V> Parameters: key - the key Returns: the greatest key less than or equal to key , or null if there is no such key Throws: ClassCastException - if the specified key cannot be compared with the keys currently in the map NullPointerException - if the specified key is null

ceilingEntry

public Map.Entry<K,V> ceilingEntry(K 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. Specified by: ceilingEntry in interface NavigableMap<K,V> Parameters: key - the key Returns: an entry with the least key greater than or equal to key , or null if there is no such key Throws: ClassCastException - if the specified key cannot be compared with the keys currently in the map NullPointerException - if the specified key is null

ceilingKey

public K ceilingKey(K key)

Description copied from interface: NavigableMap Returns the least key greater than or equal to the given key, or null if there is no such key. Specified by: ceilingKey in interface NavigableMap<K,V> Parameters: key - the key Returns: the least key greater than or equal to key , or null if there is no such key Throws: ClassCastException - if the specified key cannot be compared with the keys currently in the map NullPointerException - if the specified key is null

higherEntry

public Map.Entry<K,V> higherEntry(K 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. Specified by: higherEntry in interface NavigableMap<K,V> Parameters: key - the key Returns: an entry with the least key greater than key , or null if there is no such key Throws: ClassCastException - if the specified key cannot be compared with the keys currently in the map NullPointerException - if the specified key is null

higherKey

public K higherKey(K key)

Description copied from interface: NavigableMap Returns the least key strictly greater than the given key, or null if there is no such key. Specified by: higherKey in interface NavigableMap<K,V> Parameters: key - the key Returns: the least key greater than key , or null if there is no such key Throws: ClassCastException - if the specified key cannot be compared with the keys currently in the map NullPointerException - if the specified key is null

firstEntry

public Map.Entry<K,V> 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. Specified by: firstEntry in interface NavigableMap<K,V> Returns: an entry with the least key, or null if this map is empty

lastEntry

public Map.Entry<K,V> 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. Specified by: lastEntry in interface NavigableMap<K,V> Returns: an entry with the greatest key, or null if this map is empty

pollFirstEntry

public Map.Entry<K,V> 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. Specified by: pollFirstEntry in interface NavigableMap<K,V> Returns: the removed first entry of this map, or null if this map is empty

pollLastEntry

public Map.Entry<K,V> 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. Specified by: pollLastEntry in interface NavigableMap<K,V> Returns: the removed last entry of this map, or null if this map is empty

Java™ Platform

Standard Ed. 6