Java(TM) 2 Platform, Standard Edition, v1.2.2 API Specification: Class TreeMap - JDK 5 Documentation v1.2.2, Java 2 SDK 英文文档
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java.util
Class TreeMap
java.lang.Object | +--java.util.AbstractMap | +--java.util.TreeMap
- public class TreeMap
- extends AbstractMap
- implements SortedMap, Cloneable, Serializable
- extends AbstractMap
Red-Black tree based implementation of the SortedMap interface. This class guarantees that the map will be in ascending key order, sorted according to the natural order for the key's class (see Comparable), or by the comparator provided at 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 Corman, 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 Collections.synchronizedMap method. This is best done at creation time, to prevent accidental unsynchronized access to the map:
Map m = Collections.synchronizedMap(new TreeMap(...));
The iterators 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 or add methods, the iterator throws 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,Hashtable,Comparable,Comparator,Collection,Collections.synchronizedMap(Map), Serialized Form
| Inner classes inherited from class java.util.Map |
Map.Entry |
| Constructor Summary | |
TreeMap()
Constructs a new, empty map, sorted according to the keys' natural order. |
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TreeMap(Comparator c)
Constructs a new, empty map, sorted according to the given comparator. |
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TreeMap(Map m)
Constructs a new map containing the same mappings as the given map, sorted according to the keys' natural order. |
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TreeMap(SortedMap m)
Constructs a new map containing the same mappings as the given SortedMap, sorted according to the same ordering. |
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| Method Summary | |
void |
clear()
Removes all mappings from this TreeMap. |
Object |
clone()
Returns a shallow copy of this TreeMap instance. |
Comparator |
comparator()
Returns the comparator used to order this map, or null if this map uses its keys' natural order. |
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. |
Set |
entrySet()
Returns a set view of the mappings contained in this map. |
Object |
firstKey()
Returns the first (lowest) key currently in this sorted map. |
Object |
get(Object key)
Returns the value to which this map maps the specified key. |
SortedMap |
headMap(Object toKey)
Returns a view of the portion of this map whose keys are strictly less than toKey. |
Set |
keySet()
Returns a Set view of the keys contained in this map. |
Object |
lastKey()
Returns the last (highest) key currently in this sorted map. |
Object |
put(Object key,
Object value)
Associates the specified value with the specified key in this map. |
void |
putAll(Map map)
Copies all of the mappings from the specified map to this map. |
Object |
remove(Object key)
Removes the mapping for this key from this TreeMap if present. |
int |
size()
Returns the number of key-value mappings in this map. |
SortedMap |
subMap(Object fromKey,
Object toKey)
Returns a view of the portion of this map whose keys range from fromKey, inclusive, to toKey, exclusive. |
SortedMap |
tailMap(Object fromKey)
Returns a view of the portion of this map whose keys are greater than or equal to fromKey. |
Collection |
values()
Returns a collection view of the values contained in this map. |
| Methods inherited from class java.util.AbstractMap |
equals,
hashCode,
isEmpty,
toString |
| Methods inherited from class java.lang.Object |
finalize,
getClass,
notify,
notifyAll,
wait,
wait,
wait |
| Constructor Detail |
TreeMap
public TreeMap()
- Constructs a new, empty map, sorted according to the keys' natural
order. All keys inserted into the map must implement the
Comparable interface. Furthermore, all such keys must be
mutually comparable: k1.compareTo(k2) must not throw a
ClassCastException for any elements 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.
- See Also:
Comparable
TreeMap
public TreeMap(Comparator c)
- Constructs a new, empty map, sorted 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.
TreeMap
public TreeMap(Map m)
- Constructs a new map containing the same mappings as the given map,
sorted according to the keys' natural order. All keys inserted
into the new map must implement the Comparable interface.
Furthermore, all such keys must be mutually comparable:
k1.compareTo(k2) must not throw a ClassCastException
for any elements k1 and k2 in the map. This method
runs in n*log(n) time.
- Throws:
- ClassCastException - the keys in t are not Comparable, or are not mutually comparable.
TreeMap
public TreeMap(SortedMap m)
- Constructs a new map containing the same mappings as the given SortedMap, sorted according to the same ordering. This method runs in linear time.
| Method Detail |
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.
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.
- Throws:
- ClassCastException - if the key cannot be compared with the keys
currently in the map.
- NullPointerException - key is null and this map uses natural ordering, or its comparator does not tolerate null keys.
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 of Map.
- Overrides:
- containsValue in class AbstractMap
- Parameters:
value- value whose presence in this Map is to be tested.- Since:
- JDK1.2
get
public Object get(Object key)
- Returns the value to which this map maps the specified key. Returns
null if the map contains no mapping for this key. A return
value of 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 null. The containsKey
operation may be used to distinguish these two cases.
- Overrides:
- get in class AbstractMap
- Parameters:
key- key whose associated value is to be returned.- Returns:
- the value to which this map maps the specified key, or null if the map contains no mapping for the key.
- Throws:
- ClassCastException - key cannot be compared with the keys
currently in the map.
- NullPointerException - key is null and this map uses natural ordering, or its comparator does not tolerate null keys.
- See Also:
containsKey(Object)
comparator
public Comparator comparator()
- Returns the comparator used to order this map, or null if this
map uses its keys' natural order.
- Specified by:
- comparator in interface SortedMap
- Returns:
- the comparator associated with this sorted map, or null if it uses its keys' natural sort method.
firstKey
public Object firstKey()
- Returns the first (lowest) key currently in this sorted map.
- Returns:
- the first (lowest) key currently in this sorted map.
- Throws:
- NoSuchElementException - Map is empty.
lastKey
public Object lastKey()
- Returns the last (highest) key currently in this sorted map.
- Returns:
- the last (highest) key currently in this sorted map.
- Throws:
- NoSuchElementException - Map is empty.
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:
t- Mappings to be stored in this map.- Throws:
- ClassCastException - class of a key or value in the specified
map prevents it from being stored in this map.
- NullPointerException - this map does not permit null keys and a specified key is null.
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 this 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:
- previous value associated with specified key, or null if there was no mapping for key. A null return can also indicate that the map previously associated null with the specified key.
- Throws:
- ClassCastException - key cannot be compared with the keys
currently in the map.
- NullPointerException - key is null and this map uses natural order, or its comparator does not tolerate null keys.
remove
public Object remove(Object key)
- Removes the mapping for this key from this TreeMap if present.
- Overrides:
- remove in class AbstractMap
- Returns:
- previous value associated with specified key, or null if there was no mapping for key. A null return can also indicate that the map previously associated null with the specified key.
- Throws:
- ClassCastException - key cannot be compared with the keys
currently in the map.
- NullPointerException - key is null and this map uses natural order, or its comparator does not tolerate null keys.
clear
public void clear()
- Removes all mappings from this TreeMap.
- Overrides:
- clear in class AbstractMap
- Tags copied from interface: Map
- Throws:
- UnsupportedOperationException - clear is not supported by this map.
clone
public Object clone()
- Returns a shallow copy of this TreeMap instance. (The keys and
values themselves are not cloned.)
- Returns:
- a shallow copy of this Map.
keySet
public Set keySet()
- Returns a Set view of the keys contained in this map. The set's
iterator will return the keys in ascending order. The map is backed by
this TreeMap instance, so changes to this 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.
- Overrides:
- keySet in class AbstractMap
- Returns:
- a set view of the keys contained in this TreeMap.
values
public Collection values()
- Returns a collection view of the values contained in this map. The
collection's iterator will return the values in the order that their
corresponding keys appear in the tree. The collection is backed by
this TreeMap instance, so changes to this map are reflected in
the collection, and vice-versa. The collection supports element
removal, which removes the corresponding mapping from the map through
the Iterator.remove, Collection.remove,
removeAll, retainAll, and clear operations.
It does not support the add or addAll operations.
- Overrides:
- values in class AbstractMap
- Returns:
- a collection view of the values contained in this map.
entrySet
public Set entrySet()
- Returns a set view of the mappings contained in this map. The set's
iterator returns the mappings in ascending key order. Each element in
the returned set is a Map.Entry. The set is backed by this
map, so changes to this map are reflected in the set, and vice-versa.
The set supports element removal, which removes the corresponding
mapping from the TreeMap, through the Iterator.remove,
Set.remove, removeAll, retainAll and
clear operations. It does not support the add or
addAll operations.
- Overrides:
- entrySet in class AbstractMap
- Returns:
- a set view of the mappings contained in this map.
- See Also:
Map.Entry
subMap
public SortedMap subMap(Object fromKey, Object toKey)
- 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 sorted map
is empty.) The returned sorted map is backed by this map, so changes
in the returned sorted map are reflected in this map, and vice-versa.
The returned sorted map supports all optional map operations.
The sorted map returned by this method will throw an IllegalArgumentException if the user attempts to insert a key less than fromKey or greater than or equal to toKey.
Note: this method always returns a half-open range (which includes its low endpoint but not its high endpoint). If you need a closed range (which includes both endpoints), and the key type allows for calculation of the successor a given key, merely request the subrange from lowEndpoint to successor(highEndpoint). For example, suppose that m is a sorted map whose keys are strings. The following idiom obtains a view containing all of the key-value mappings in m whose keys are between low and high, inclusive:
SortedMap sub = m.submap(low, high+"\0");
A similar technique can be used to generate an open range (which contains neither endpoint). The following idiom obtains a view containing all of the key-value mappings in m whose keys are between low and high, exclusive:SortedMap sub = m.subMap(low+"\0", high);
- Parameters:
fromKey- low endpoint (inclusive) of the subMap.toKey- high endpoint (exclusive) of the subMap.- Returns:
- a view of the portion of this map whose keys range from fromKey, inclusive, to toKey, exclusive.
- Throws:
- NullPointerException - if fromKey or toKey is
null and this map uses natural order, or its
comparator does not tolerate null keys.
- IllegalArgumentException - if fromKey is greater than toKey.
headMap
public SortedMap headMap(Object toKey)
- Returns a view of the portion of this map whose keys are strictly less
than toKey. The returned sorted map is backed by this map, so
changes in the returned sorted map are reflected in this map, and
vice-versa. The returned sorted map supports all optional map
operations.
The sorted map returned by this method will throw an IllegalArgumentException if the user attempts to insert a key greater than or equal to toKey.
Note: this method always returns a view that does not contain its (high) endpoint. If you need a view that does contain this endpoint, and the key type allows for calculation of the successor a given key, merely request a headMap bounded by successor(highEndpoint). For example, suppose that suppose that m is a sorted map whose keys are strings. The following idiom obtains a view containing all of the key-value mappings in m whose keys are less than or equal to high:
SortedMap head = m.headMap(high+"\0");- Parameters:
toKey- high endpoint (exclusive) of the headMap.- Returns:
- a view of the portion of this map whose keys are strictly less than toKey.
- Throws:
- NullPointerException - if toKey is null and this map uses natural order, or its comparator does * not tolerate null keys.
tailMap
public SortedMap tailMap(Object fromKey)
- Returns a view of the portion of this map whose keys are greater than
or equal to fromKey. The returned sorted map is backed by
this map, so changes in the returned sorted map are reflected in this
map, and vice-versa. The returned sorted map supports all optional map
operations.
The sorted map returned by this method will throw an IllegalArgumentException if the user attempts to insert a key less than fromKey.
Note: this method always returns a view that contains its (low) endpoint. If you need a view that does not contain this endpoint, and the element type allows for calculation of the successor a given value, merely request a tailMap bounded by successor(lowEndpoint). For For example, suppose that suppose that m is a sorted map whose keys are strings. The following idiom obtains a view containing all of the key-value mappings in m whose keys are strictly greater than low:
SortedMap tail = m.tailMap(low+"\0");- Parameters:
fromKey- low endpoint (inclusive) of the tailMap.- Returns:
- a view of the portion of this map whose keys are greater than or equal to fromKey.
- Throws:
- NullPointerException - fromKey is null and this map uses natural ordering, or its comparator does not tolerate null keys.
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