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Class java.util.TreeMap

java.lang.Object
    |
    +----java.util.AbstractMap
            |
            +----java.util.TreeMap

public class TreeMap

extends AbstractMap

implements Map, Serializable

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

Note that this implementation is not synchronized. If multiple threads access a TreeMap concurrently, and at least one of the threads modifies the TreeMap 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 a key that is already contained in the Table is not a structural modification.) This is typically accomplished by synchronizing on some object that naturally encapsulates the TreeMap. If no such object exists, the TreeMap should be "wrapped" using the Collections.synchronizedSet method. This is best done at creation time, to prevent accidental unsynchronized access to the TreeMap:

	Map m = Collections.synchronizedMap(new TreeMap(...));
 

The Iterators returned by the iterator methods of the Collections returned by all of TreeMap's "collection view methods" are fail-fast: if the TreeMap is structurally modified at any time after the Iterator is created, in any way except through the Iterator's own remove or add methods, the Iterator will throw a 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.

Since:

JDK1.2

See Also:

Map, HashMap, ArrayMap, Hashtable, Comparable, Comparator, Collection, synchronizedMap

TreeMap()

Constructs a new, empty TreeMap, sorted according to the keys' natural sort method.

TreeMap(Comparator)

Constructs a new, empty TreeMap, sorted according to the given comparator.

TreeMap(Map)

Constructs a new TreeMap containing the same mappings as the given Map, sorted according to the keys' natural sort method.

clear()

Removes all mappings from this TreeMap.

containsKey(Object)

Returns true if this TreeMap contains a mapping for the specified key.

entries()

Returns a Collection view of the mappings contained in this Map.

get(Object)

Returns the value to which this TreeMap maps the specified key.

keySet()

Returns a Set view of the keys contained in this TreeMap.

put(Object, Object)

Associates the specified value with the specified key in this TreeMap.

remove(Object)

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

size()

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

subMap(Object, Object)

Returns a view of the portion of this TreeMap whose keys range from fromKey, inclusive, to toKey, exclusive.

values()

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

public TreeMap()

Constructs a new, empty TreeMap, sorted according to the keys' natural sort method. All keys inserted into the TreeMap must implement the Comparable interface. Furthermore, all such keys must be mutually comparable: k1.compareTo(k2) must not throw a typeMismatchException for any elements k1 and k2 in the TreeMap. If the user attempts to put a key into the TreeMap that violates this constraint (for example, the user attempts to put a String key into a TreeMap whose keys are Integers), the put(Object key, Object value) call will throw a ClassCastException.

See Also:

Comparable

public TreeMap(Comparator c)

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

public TreeMap(Map t)

Constructs a new TreeMap containing the same mappings as the given Map, sorted according to the keys' natural sort method. All keys inserted into the TreeMap must implement the Comparable interface. Furthermore, all such keys must be mutually comparable: k1.compareTo(k2) must not throw a typeMismatchException for any elements k1 and k2 in the TreeMap.

Throws: ClassCastException

the keys in t are not Comparable, or are not mutually comparable.

public int size()

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

Overrides:

size in class AbstractMap

public boolean containsKey(Object key)

Returns true if this TreeMap contains a mapping for the specified key.

Parameters:

key - key whose presence in this Map is to be tested.

Throws: ClassCastException

key cannot be compared with the keys currently in the TreeMap.

Throws: NullPointerException

key is null and this TreeMap uses natural sort method, or its comparator does not tolerate null keys.

Overrides:

containsKey in class AbstractMap

public Object get(Object key)

Returns the value to which this TreeMap maps the specified key. Returns null if the TreeMap contains no mapping for this key. A return value of null does not necessarily indicate that the TreeMap contains no mapping for the key; it's also possible that the TreeMap explicitly maps the key to null. The containsKey operation may be used to distinguish these two cases.

Parameters:

key - key whose associated value is to be returned.

Throws: ClassCastException

key cannot be compared with the keys currently in the TreeMap.

Throws: NullPointerException

key is null and this TreeMap uses natural sort method, or its comparator does not tolerate null keys.

Overrides:

get in class AbstractMap

See Also:

containsKey

public Object put(Object key,
                  Object value)

Associates the specified value with the specified key in this TreeMap. If the TreeMap previously contained a mapping for this 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:

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

Throws: ClassCastException

key cannot be compared with the keys currently in the TreeMap.

Throws: NullPointerException

key is null and this TreeMap uses natural sort method, or its comparator does not tolerate null keys.

Overrides:

put in class AbstractMap

public Object remove(Object key)

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

Returns:

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

Throws: ClassCastException

key cannot be compared with the keys currently in the TreeMap.

Throws: NullPointerException

key is null and this TreeMap uses natural sort method, or its comparator does not tolerate null keys.

Overrides:

remove in class AbstractMap

public void clear()

Removes all mappings from this TreeMap.

Overrides:

clear in class AbstractMap

public Set keySet()

Returns a Set view of the keys contained in this TreeMap. The Set's Iterator will return the keys in ascending order. The Set is backed by the TreeMap, so changes to the TreeMap are reflected in the Set, and vice-versa. The Set supports element removal, which removes the corresponding mapping from the TreeMap, 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

public Collection values()

Returns a Collection view of the values contained in this TreeMap. The Collection's iterator will return the values in the order that their corresponding keys appear in the tree. The Collection is backed by the TreeMap, so changes to the TreeMap are reflected in the Collection, and vice-versa. The Collection supports element removal, which removes the corresponding mapping from the TreeMap, 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

public Collection entries()

Returns a Collection view of the mappings contained in this Map. The Collection's Iterator will return the mappings in ascending Key order. Each element in the returned collection is a Map.Entry. The Collection is backed by the TreeMap, so changes to the TreeMap are reflected in the Collection, and vice-versa. The Collection supports element removal, which removes the corresponding mapping from the TreeMap, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

Overrides:

entries in class AbstractMap

See Also:

Map.Entry

public Map subMap(Object fromKey,
                  Object toKey)

Returns a view of the portion of this TreeMap whose keys range from fromKey, inclusive, to toKey, exclusive. The returned Map is backed by this TreeMap, so changes in the returned Map are reflected in this TreeMap, and vice-versa. The returned Map supports all optional Map operations. It does not support the subMap operation, as it is not a TreeMap.

Parameters:

fromKey - low endpoint (inclusive) of the subMap.

fromKey - high endpoint (exclusive) of the subMap.

Throws: ClassCastException

fromKey or toKey cannot be compared with the keys currently in the TreeMap.

Throws: NullPointerException

fromKey or toKey is null and this TreeMap uses natural sort method, or its comparator does not tolerate null keys.

Throws: IllegalArgumentException

fromKey is greater than toKey.

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