java.util
class TreeMap

java.lang.Object java.util.AbstractMap java.util.TreeMap

All Implemented Interfaces:

Serializable, Cloneable, Map, NavigableMap

Most common way to construct:

TreeMap tm = new TreeMap();

Based on 50 examples

public class TreeMap
extends AbstractMap
implements NavigableMap, Cloneable, Serializable

A Red-Black tree based {@link NavigableMap} implementation. The map is sorted according to the {@linkplain Comparable natural ordering} of its keys, or by a {@link Comparator} provided at map creation time, depending on which constructor is used.

This implementation provides guaranteed log(n) time cost for the containsKey, get, put and remove operations. Algorithms are adaptations of those in Cormen, Leiserson, and Rivest's Introduction to Algorithms.

Note that the ordering maintained by a sorted map (whether or not an explicit comparator is provided) must be consistent with equals if this sorted map is to correctly implement the Map interface. (See Comparable or Comparator for a precise definition of consistent with equals.) This is so because the Map interface is defined in terms of the equals operation, but a map performs all key comparisons using its compareTo (or compare) method, so two keys that are deemed equal by this method are, from the standpoint of the sorted map, equal. The behavior of a sorted map is well-defined even if its ordering is inconsistent with equals; it just fails to obey the general contract of the Map interface.

Note that this implementation is not synchronized. If multiple threads access a map concurrently, and at least one of the threads modifies the map structurally, it must be synchronized externally. (A structural modification is any operation that adds or deletes one or more mappings; merely changing the value associated with an existing key is not a structural modification.) This is typically accomplished by synchronizing on some object that naturally encapsulates the map. If no such object exists, the map should be "wrapped" using the {@link Collections#synchronizedSortedMap Collections.synchronizedSortedMap} method. This is best done at creation time, to prevent accidental unsynchronized access to the map:

   SortedMap m = Collections.synchronizedSortedMap(new TreeMap(...));

The iterators returned by the iterator method of the collections returned by all of this class's "collection view methods" are fail-fast: if the map is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove method, the iterator will throw a {@link ConcurrentModificationException}. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.

Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs.

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.)

This class is a member of the Java Collections Framework.

TreeMap

public TreeMap()

Constructs a new, empty tree map, using the natural ordering of its keys. All keys inserted into the map must implement the {@link Comparable} interface. Furthermore, all such keys must be mutually comparable: k1.compareTo(k2) must not throw a ClassCastException for any keys k1 and k2 in the map. If the user attempts to put a key into the map that violates this constraint (for example, the user attempts to put a string key into a map whose keys are integers), the put(Object key, Object value) call will throw a ClassCastException.

TreeMap

public TreeMap(Comparator comparator)

Constructs a new, empty tree map, ordered according to the given comparator. All keys inserted into the map must be mutually comparable by the given comparator: comparator.compare(k1, k2) must not throw a ClassCastException for any keys k1 and k2 in the map. If the user attempts to put a key into the map that violates this constraint, the put(Object key, Object value) call will throw a ClassCastException.

Parameters:

comparator - the comparator that will be used to order this map. If null, the {@linkplain Comparable natural ordering} of the keys will be used.

TreeMap

public TreeMap(Map m)

Constructs a new tree map containing the same mappings as the given map, ordered according to the natural ordering of its keys. All keys inserted into the new map must implement the {@link Comparable} interface. Furthermore, all such keys must be mutually comparable: k1.compareTo(k2) must not throw a ClassCastException for any keys k1 and k2 in the map. This method runs in n*log(n) time.

Parameters:

m - the map whose mappings are to be placed in this map

TreeMap

public TreeMap(SortedMap m)

Constructs a new tree map containing the same mappings and using the same ordering as the specified sorted map. This method runs in linear time.

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

ceilingEntry

public Map.Entry ceilingEntry(Object key)

Parameters:

key

ceilingKey

public Object ceilingKey(Object key)

Parameters:

key

clear

public void clear()

Removes all of the mappings from this map. The map will be empty after this call returns.

Overrides:

clear in class AbstractMap

clone

public Object clone()

Returns a shallow copy of this TreeMap instance. (The keys and values themselves are not cloned.)

Overrides:

clone in class AbstractMap

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.

Overrides:

containsKey in class AbstractMap

Parameters:

key - key whose presence in this map is to be tested

Returns:

true if this map contains a mapping for the specified key

containsValue

public boolean containsValue(Object value)

Returns true if this map maps one or more keys to the specified value. More formally, returns true if and only if this map contains at least one mapping to a value v such that (value==null ? v==null : value.equals(v)). This operation will probably require time linear in the map size for most implementations.

Overrides:

containsValue in class AbstractMap

Parameters:

value - value whose presence in this map is to be tested

Returns:

true if a mapping to value exists; false otherwise

descendingKeySet

public NavigableSet descendingKeySet()

descendingMap

public NavigableMap descendingMap()

entrySet

public Set entrySet()

Returns a {@link 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. If the map is modified while an iteration over the set is in progress (except through the iterator's own remove operation, or through the setValue operation on a map entry returned by the iterator) the results of the iteration are undefined. 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.

Overrides:

entrySet in class AbstractMap

firstEntry

public Map.Entry firstEntry()

firstKey

public Object firstKey()

floorEntry

public Map.Entry floorEntry(Object key)

Parameters:

key

floorKey

public Object floorKey(Object key)

Parameters:

key

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.)

A return value of {@code null} does not necessarily indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key to {@code null}. The {@link #containsKey containsKey} operation may be used to distinguish these two cases.

Overrides:

get in class AbstractMap

Parameters:

key

headMap

public SortedMap headMap(Object toKey)

Parameters:

toKey

headMap

public NavigableMap headMap(Object toKey,
                            boolean inclusive)

Parameters:

toKey

inclusive

higherEntry

public Map.Entry higherEntry(Object key)

Parameters:

key

higherKey

public Object higherKey(Object key)

Parameters:

key

keySet

public Set keySet()

Returns a {@link Set} 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. If the map is modified while an iteration over the set is in progress (except through the iterator's own remove operation), the results of the iteration are undefined. 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.

Overrides:

keySet in class AbstractMap

lastEntry

public Map.Entry lastEntry()

lastKey

public Object lastKey()

lowerEntry

public Map.Entry lowerEntry(Object key)

Parameters:

key

lowerKey

public Object lowerKey(Object key)

Parameters:

key

navigableKeySet

public NavigableSet navigableKeySet()

pollFirstEntry

public Map.Entry pollFirstEntry()

pollLastEntry

public Map.Entry pollLastEntry()

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.

Overrides:

put in class AbstractMap

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 key, or null if there was no mapping for key. (A null return can also indicate that the map previously associated null with key.)

putAll

public void putAll(Map map)

Copies all of the mappings from the specified map to this map. These mappings replace any mappings that this map had for any of the keys currently in the specified map.

Overrides:

putAll in class AbstractMap

Parameters:

map - mappings to be stored in this map

remove

public Object remove(Object key)

Removes the mapping for this key from this TreeMap if present.

Overrides:

remove in class AbstractMap

Parameters:

key - key for which mapping should be removed

Returns:

the previous value associated with key, or null if there was no mapping for key. (A null return can also indicate that the map previously associated null with key.)

size

public int size()

Returns the number of key-value mappings in this map.

Overrides:

size in class AbstractMap

Returns:

the number of key-value mappings in this map

subMap

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

Parameters:

fromKey

fromInclusive

toKey

toInclusive

subMap

public SortedMap subMap(Object fromKey,
                        Object toKey)

Parameters:

fromKey

toKey

tailMap

public SortedMap tailMap(Object fromKey)

Parameters:

fromKey

tailMap

public NavigableMap tailMap(Object fromKey,
                            boolean inclusive)

Parameters:

fromKey

inclusive

values

public Collection values()

Returns a {@link 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. If the map is modified while an iteration over the collection is in progress (except through the iterator's own remove operation), the results of the iteration are undefined. 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.

Overrides:

values in class AbstractMap