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java.util

Class TreeMap<K,V>

public class TreeMap<K,V> extends AbstractMap<K,V> implements NavigableMap<K,V>, Cloneable, Serializable

This class provides a red-black tree implementation of the SortedMap interface. Elements in the Map will be sorted by either a user-provided Comparator object, or by the natural ordering of the keys. The algorithms are adopted from Corman, Leiserson, and Rivest's Introduction to Algorithms. TreeMap guarantees O(log n) insertion and deletion of elements. That being said, there is a large enough constant coefficient in front of that "log n" (overhead involved in keeping the tree balanced), that TreeMap may not be the best choice for small collections. If something is already sorted, you may want to just use a LinkedHashMap to maintain the order while providing O(1) access. TreeMap is a part of the JDK1.2 Collections API. Null keys are allowed only if a Comparator is used which can deal with them; natural ordering cannot cope with null. Null values are always allowed. Note that the ordering must be consistent with equals to correctly implement the Map interface. If this condition is violated, the map is still well-behaved, but you may have suprising results when comparing it to other maps.

This implementation is not synchronized. If you need to share this between multiple threads, do something like:
SortedMap m = Collections.synchronizedSortedMap(new TreeMap(...));

The iterators are fail-fast, meaning that any structural modification, except for remove() called on the iterator itself, cause the iterator to throw a ConcurrentModificationException rather than exhibit non-deterministic behavior.

Since: 1.2

See Also: Map HashMap Hashtable LinkedHashMap Comparable Comparator Collection synchronizedSortedMap

UNKNOWN: updated to 1.6

Constructor Summary
TreeMap()
Instantiate a new TreeMap with no elements, using the keys' natural ordering to sort.
TreeMap(Comparator<? super K> c)
Instantiate a new TreeMap with no elements, using the provided comparator to sort.
TreeMap(Map<? extends K,? extends V> map)
Instantiate a new TreeMap, initializing it with all of the elements in the provided Map.
TreeMap(SortedMap<K,? extends V> sm)
Instantiate a new TreeMap, initializing it with all of the elements in the provided SortedMap.
Method Summary
Entry<K,V>ceilingEntry(K key)
Returns the entry associated with the least or lowest key that is greater than or equal to the specified key, or null if there is no such key.
KceilingKey(K key)
Returns the the least or lowest key that is greater than or equal to the specified key, or null if there is no such key.
voidclear()
Clears the Map so it has no keys.
Objectclone()
Returns a shallow clone of this TreeMap.
Comparator<? super K>comparator()
Return the comparator used to sort this map, or null if it is by natural order.
booleancontainsKey(Object key)
Returns true if the map contains a mapping for the given key.
booleancontainsValue(Object value)
Returns true if the map contains at least one mapping to the given value.
NavigableSet<K>descendingKeySet()
Returns a reverse ordered {@link NavigableSet} view of this map's keys.
NavigableMap<K,V>descendingMap()
Returns a view of the map in reverse order.
Set<Entry<K,V>>entrySet()
Returns a "set view" of this TreeMap's entries.
Entry<K,V>firstEntry()
Returns the entry associated with the least or lowest key in the map, or null if the map is empty.
KfirstKey()
Returns the first (lowest) key in the map.
Entry<K,V>floorEntry(K key)
Returns the entry associated with the greatest or highest key that is less than or equal to the specified key, or null if there is no such key.
KfloorKey(K key)
Returns the the greatest or highest key that is less than or equal to the specified key, or null if there is no such key.
Vget(Object key)
Return the value in this TreeMap associated with the supplied key, or null if the key maps to nothing.
SortedMap<K,V>headMap(K toKey)
Returns a view of this Map including all entries with keys less than toKey.
NavigableMap<K,V>headMap(K toKey, boolean inclusive)
Returns a view of this Map including all entries with keys less than (or equal to, if inclusive is true) toKey.
Entry<K,V>higherEntry(K key)
Returns the entry associated with the least or lowest key that is strictly greater than the specified key, or null if there is no such key.
KhigherKey(K key)
Returns the the least or lowest key that is strictly greater than the specified key, or null if there is no such key.
Set<K>keySet()
Returns a "set view" of this TreeMap's keys.
Entry<K,V>lastEntry()
Returns the entry associated with the greatest or highest key in the map, or null if the map is empty.
KlastKey()
Returns the last (highest) key in the map.
Entry<K,V>lowerEntry(K key)
Returns the entry associated with the greatest or highest key that is strictly less than the specified key, or null if there is no such key.
KlowerKey(K key)
Returns the the greatest or highest key that is strictly less than the specified key, or null if there is no such key.
NavigableSet<K>navigableKeySet()
Returns a {@link NavigableSet} view of this map's keys.
Entry<K,V>pollFirstEntry()
Removes and returns the entry associated with the least or lowest key in the map, or null if the map is empty.
Entry<K,V>pollLastEntry()
Removes and returns the entry associated with the greatest or highest key in the map, or null if the map is empty.
Vput(K key, V value)
Puts the supplied value into the Map, mapped by the supplied key.
voidputAll(Map<? extends K,? extends V> m)
Copies all elements of the given map into this TreeMap.
Vremove(Object key)
Removes from the TreeMap and returns the value which is mapped by the supplied key.
intsize()
Returns the number of key-value mappings currently in this Map.
SortedMap<K,V>subMap(K fromKey, K toKey)
Returns a view of this Map including all entries with keys greater or equal to fromKey and less than toKey (a half-open interval).
NavigableMap<K,V>subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive)
Returns a view of this Map including all entries with keys greater (or equal to, if fromInclusive is true) fromKey and less than (or equal to, if toInclusive is true) toKey.
SortedMap<K,V>tailMap(K fromKey)
Returns a view of this Map including all entries with keys greater or equal to fromKey.
NavigableMap<K,V>tailMap(K fromKey, boolean inclusive)
Returns a view of this Map including all entries with keys greater or equal to fromKey.
Collection<V>values()
Returns a "collection view" (or "bag view") of this TreeMap's values.

Constructor Detail

TreeMap

public TreeMap()
Instantiate a new TreeMap with no elements, using the keys' natural ordering to sort. All entries in the map must have a key which implements Comparable, and which are mutually comparable, otherwise map operations may throw a {@link ClassCastException}. Attempts to use a null key will throw a {@link NullPointerException}.

See Also: Comparable

TreeMap

public TreeMap(Comparator<? super K> c)
Instantiate a new TreeMap with no elements, using the provided comparator to sort. All entries in the map must have keys which are mutually comparable by the Comparator, otherwise map operations may throw a {@link ClassCastException}.

Parameters: c the sort order for the keys of this map, or null for the natural order

TreeMap

public TreeMap(Map<? extends K,? extends V> map)
Instantiate a new TreeMap, initializing it with all of the elements in the provided Map. The elements will be sorted using the natural ordering of the keys. This algorithm runs in n*log(n) time. All entries in the map must have keys which implement Comparable and are mutually comparable, otherwise map operations may throw a {@link ClassCastException}.

Parameters: map a Map, whose entries will be put into this TreeMap

Throws: ClassCastException if the keys in the provided Map are not comparable NullPointerException if map is null

See Also: Comparable

TreeMap

public TreeMap(SortedMap<K,? extends V> sm)
Instantiate a new TreeMap, initializing it with all of the elements in the provided SortedMap. The elements will be sorted using the same comparator as in the provided SortedMap. This runs in linear time.

Parameters: sm a SortedMap, whose entries will be put into this TreeMap

Throws: NullPointerException if sm is null

Method Detail

ceilingEntry

public Entry<K,V> ceilingEntry(K key)
Returns the entry associated with the least or lowest key that is greater than or equal to the specified key, or null if there is no such key.

Parameters: key the key relative to the returned entry.

Returns: the entry with the least key greater than or equal to the given key, or null if there is no such key.

Throws: ClassCastException if the specified key can not be compared with those in the map. NullPointerException if the key is null and this map either uses natural ordering or a comparator that does not permit null keys.

Since: 1.6

ceilingKey

public K ceilingKey(K key)
Returns the the least or lowest key that is greater than or equal to the specified key, or null if there is no such key.

Parameters: key the key relative to the returned entry.

Returns: the least key greater than or equal to the given key, or null if there is no such key.

Throws: ClassCastException if the specified key can not be compared with those in the map. NullPointerException if the key is null and this map either uses natural ordering or a comparator that does not permit null keys.

Since: 1.6

clear

public void clear()
Clears the Map so it has no keys. This is O(1).

clone

public Object clone()
Returns a shallow clone of this TreeMap. The Map itself is cloned, but its contents are not.

Returns: the clone

comparator

public Comparator<? super K> comparator()
Return the comparator used to sort this map, or null if it is by natural order.

Returns: the map's comparator

containsKey

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

Parameters: key the key to look for

Returns: true if the key has a mapping

Throws: ClassCastException if key is not comparable to map elements NullPointerException if key is null and the comparator is not tolerant of nulls

containsValue

public boolean containsValue(Object value)
Returns true if the map contains at least one mapping to the given value. This requires linear time.

Parameters: value the value to look for

Returns: true if the value appears in a mapping

descendingKeySet

public NavigableSet<K> descendingKeySet()
Returns a reverse ordered {@link NavigableSet} view of this map's keys. The set is backed by the {@link TreeMap}, so changes in one show up in the other. The set supports element removal, but not element addition.

Returns: a reverse ordered set view of the keys.

Since: 1.6

See Also: descendingMap

descendingMap

public NavigableMap<K,V> descendingMap()
Returns a view of the map in reverse order. The descending map is backed by the original map, so that changes affect both maps. Any changes occurring to either map while an iteration is taking place (with the exception of a {@link Iterator#remove()} operation) result in undefined behaviour from the iteration. The ordering of the descending map is the same as for a map with a {@link Comparator} given by {@link Collections#reverseOrder()}, and calling {@link #descendingMap()} on the descending map itself results in a view equivalent to the original map.

Returns: a reverse order view of the map.

Since: 1.6

entrySet

public Set<Entry<K,V>> entrySet()
Returns a "set view" of this TreeMap's entries. The set is backed by the TreeMap, so changes in one show up in the other. The set supports element removal, but not element addition.

Note that the iterators for all three views, from keySet(), entrySet(), and values(), traverse the TreeMap in sorted sequence.

Returns: a set view of the entries

See Also: keySet values Entry

firstEntry

public Entry<K,V> firstEntry()
Returns the entry associated with the least or lowest key in the map, or null if the map is empty.

Returns: the lowest entry, or null if the map is empty.

Since: 1.6

firstKey

public K firstKey()
Returns the first (lowest) key in the map.

Returns: the first key

Throws: NoSuchElementException if the map is empty

floorEntry

public Entry<K,V> floorEntry(K key)
Returns the entry associated with the greatest or highest key that is less than or equal to the specified key, or null if there is no such key.

Parameters: key the key relative to the returned entry.

Returns: the entry with the greatest key less than or equal to the given key, or null if there is no such key.

Throws: ClassCastException if the specified key can not be compared with those in the map. NullPointerException if the key is null and this map either uses natural ordering or a comparator that does not permit null keys.

Since: 1.6

floorKey

public K floorKey(K key)
Returns the the greatest or highest key that is less than or equal to the specified key, or null if there is no such key.

Parameters: key the key relative to the returned entry.

Returns: the greatest key less than or equal to the given key, or null if there is no such key.

Throws: ClassCastException if the specified key can not be compared with those in the map. NullPointerException if the key is null and this map either uses natural ordering or a comparator that does not permit null keys.

Since: 1.6

get

public V get(Object key)
Return the value in this TreeMap associated with the supplied key, or null if the key maps to nothing. NOTE: Since the value could also be null, you must use containsKey to see if this key actually maps to something.

Parameters: key the key for which to fetch an associated value

Returns: what the key maps to, if present

Throws: ClassCastException if key is not comparable to elements in the map NullPointerException if key is null but the comparator does not tolerate nulls

See Also: TreeMap containsKey

headMap

public SortedMap<K,V> headMap(K toKey)
Returns a view of this Map including all entries with keys less than toKey. The returned map is backed by the original, so changes in one appear in the other. The submap will throw an {@link IllegalArgumentException} for any attempt to access or add an element beyond the specified cutoff. The returned map does not include the endpoint; if you want inclusion, pass the successor element or call headMap(toKey, true). This is equivalent to calling headMap(toKey, false).

Parameters: toKey the (exclusive) cutoff point

Returns: a view of the map less than the cutoff

Throws: ClassCastException if toKey is not compatible with the comparator (or is not Comparable, for natural ordering) NullPointerException if toKey is null, but the comparator does not tolerate null elements

headMap

public NavigableMap<K,V> headMap(K toKey, boolean inclusive)
Returns a view of this Map including all entries with keys less than (or equal to, if inclusive is true) toKey. The returned map is backed by the original, so changes in one appear in the other. The submap will throw an {@link IllegalArgumentException} for any attempt to access or add an element beyond the specified cutoff.

Parameters: toKey the cutoff point inclusive true if the cutoff point should be included.

Returns: a view of the map less than (or equal to, if inclusive is true) the cutoff.

Throws: ClassCastException if toKey is not compatible with the comparator (or is not Comparable, for natural ordering) NullPointerException if toKey is null, but the comparator does not tolerate null elements

higherEntry

public Entry<K,V> higherEntry(K key)
Returns the entry associated with the least or lowest key that is strictly greater than the specified key, or null if there is no such key.

Parameters: key the key relative to the returned entry.

Returns: the entry with the least key greater than the given key, or null if there is no such key.

Throws: ClassCastException if the specified key can not be compared with those in the map. NullPointerException if the key is null and this map either uses natural ordering or a comparator that does not permit null keys.

Since: 1.6

higherKey

public K higherKey(K key)
Returns the the least or lowest key that is strictly greater than the specified key, or null if there is no such key.

Parameters: key the key relative to the returned entry.

Returns: the least key greater than the given key, or null if there is no such key.

Throws: ClassCastException if the specified key can not be compared with those in the map. NullPointerException if the key is null and this map either uses natural ordering or a comparator that does not permit null keys.

Since: 1.6

keySet

public Set<K> keySet()
Returns a "set view" of this TreeMap's keys. The set is backed by the TreeMap, so changes in one show up in the other. The set supports element removal, but not element addition.

Returns: a set view of the keys

See Also: values entrySet

lastEntry

public Entry<K,V> lastEntry()
Returns the entry associated with the greatest or highest key in the map, or null if the map is empty.

Returns: the highest entry, or null if the map is empty.

Since: 1.6

lastKey

public K lastKey()
Returns the last (highest) key in the map.

Returns: the last key

Throws: NoSuchElementException if the map is empty

lowerEntry

public Entry<K,V> lowerEntry(K key)
Returns the entry associated with the greatest or highest key that is strictly less than the specified key, or null if there is no such key.

Parameters: key the key relative to the returned entry.

Returns: the entry with the greatest key less than the given key, or null if there is no such key.

Throws: ClassCastException if the specified key can not be compared with those in the map. NullPointerException if the key is null and this map either uses natural ordering or a comparator that does not permit null keys.

Since: 1.6

lowerKey

public K lowerKey(K key)
Returns the the greatest or highest key that is strictly less than the specified key, or null if there is no such key.

Parameters: key the key relative to the returned entry.

Returns: the greatest key less than the given key, or null if there is no such key.

Throws: ClassCastException if the specified key can not be compared with those in the map. NullPointerException if the key is null and this map either uses natural ordering or a comparator that does not permit null keys.

Since: 1.6

navigableKeySet

public NavigableSet<K> navigableKeySet()
Returns a {@link NavigableSet} view of this map's keys. The set is backed by the {@link TreeMap}, so changes in one show up in the other. Any changes occurring to either while an iteration is taking place (with the exception of a {@link Iterator#remove()} operation) result in undefined behaviour from the iteration. The ordering The set supports element removal, but not element addition.

Returns: a {@link NavigableSet} view of the keys.

Since: 1.6

pollFirstEntry

public Entry<K,V> pollFirstEntry()
Removes and returns the entry associated with the least or lowest key in the map, or null if the map is empty.

Returns: the removed first entry, or null if the map is empty.

Since: 1.6

pollLastEntry

public Entry<K,V> pollLastEntry()
Removes and returns the entry associated with the greatest or highest key in the map, or null if the map is empty.

Returns: the removed last entry, or null if the map is empty.

Since: 1.6

put

public V put(K key, V value)
Puts the supplied value into the Map, mapped by the supplied key. The value may be retrieved by any object which equals() this key. NOTE: Since the prior value could also be null, you must first use containsKey if you want to see if you are replacing the key's mapping.

Parameters: key the key used to locate the value value the value to be stored in the Map

Returns: the prior mapping of the key, or null if there was none

Throws: ClassCastException if key is not comparable to current map keys NullPointerException if key is null, but the comparator does not tolerate nulls

See Also: get equals

putAll

public void putAll(Map<? extends K,? extends V> m)
Copies all elements of the given map into this TreeMap. If this map already has a mapping for a key, the new mapping replaces the current one.

Parameters: m the map to be added

Throws: ClassCastException if a key in m is not comparable with keys in the map NullPointerException if a key in m is null, and the comparator does not tolerate nulls

remove

public V remove(Object key)
Removes from the TreeMap and returns the value which is mapped by the supplied key. If the key maps to nothing, then the TreeMap remains unchanged, and null is returned. NOTE: Since the value could also be null, you must use containsKey to see if you are actually removing a mapping.

Parameters: key the key used to locate the value to remove

Returns: whatever the key mapped to, if present

Throws: ClassCastException if key is not comparable to current map keys NullPointerException if key is null, but the comparator does not tolerate nulls

size

public int size()
Returns the number of key-value mappings currently in this Map.

Returns: the size

subMap

public SortedMap<K,V> subMap(K fromKey, K toKey)
Returns a view of this Map including all entries with keys greater or equal to fromKey and less than toKey (a half-open interval). The returned map is backed by the original, so changes in one appear in the other. The submap will throw an {@link IllegalArgumentException} for any attempt to access or add an element beyond the specified cutoffs. The returned map includes the low endpoint but not the high; if you want to reverse this behavior on either end, pass in the successor element or call {@link #subMap(K,boolean,K,boolean)}. This call is equivalent to subMap(fromKey, true, toKey, false).

Parameters: fromKey the (inclusive) low cutoff point toKey the (exclusive) high cutoff point

Returns: a view of the map between the cutoffs

Throws: ClassCastException if either cutoff is not compatible with the comparator (or is not Comparable, for natural ordering) NullPointerException if fromKey or toKey is null, but the comparator does not tolerate null elements IllegalArgumentException if fromKey is greater than toKey

subMap

public NavigableMap<K,V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive)
Returns a view of this Map including all entries with keys greater (or equal to, if fromInclusive is true) fromKey and less than (or equal to, if toInclusive is true) toKey. The returned map is backed by the original, so changes in one appear in the other. The submap will throw an {@link IllegalArgumentException} for any attempt to access or add an element beyond the specified cutoffs.

Parameters: fromKey the low cutoff point fromInclusive true if the low cutoff point should be included. toKey the high cutoff point toInclusive true if the high cutoff point should be included.

Returns: a view of the map for the specified range.

Throws: ClassCastException if either cutoff is not compatible with the comparator (or is not Comparable, for natural ordering) NullPointerException if fromKey or toKey is null, but the comparator does not tolerate null elements IllegalArgumentException if fromKey is greater than toKey

tailMap

public SortedMap<K,V> tailMap(K fromKey)
Returns a view of this Map including all entries with keys greater or equal to fromKey. The returned map is backed by the original, so changes in one appear in the other. The submap will throw an {@link IllegalArgumentException} for any attempt to access or add an element beyond the specified cutoff. The returned map includes the endpoint; if you want to exclude it, pass in the successor element. This is equivalent to calling tailMap(fromKey, true).

Parameters: fromKey the (inclusive) low cutoff point

Returns: a view of the map above the cutoff

Throws: ClassCastException if fromKey is not compatible with the comparator (or is not Comparable, for natural ordering) NullPointerException if fromKey is null, but the comparator does not tolerate null elements

tailMap

public NavigableMap<K,V> tailMap(K fromKey, boolean inclusive)
Returns a view of this Map including all entries with keys greater or equal to fromKey. The returned map is backed by the original, so changes in one appear in the other. The submap will throw an {@link IllegalArgumentException} for any attempt to access or add an element beyond the specified cutoff. The returned map includes the endpoint; if you want to exclude it, pass in the successor element.

Parameters: fromKey the low cutoff point inclusive true if the cutoff point should be included.

Returns: a view of the map above the cutoff

Throws: ClassCastException if fromKey is not compatible with the comparator (or is not Comparable, for natural ordering) NullPointerException if fromKey is null, but the comparator does not tolerate null elements

values

public Collection<V> values()
Returns a "collection view" (or "bag view") of this TreeMap's values. The collection is backed by the TreeMap, so changes in one show up in the other. The collection supports element removal, but not element addition.

Returns: a bag view of the values

See Also: keySet entrySet

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Summary: Nested Field Constr Method Detail: Field Constr Method