Class java.util.TreeMap
java.lang.Object
|
+--java.util.AbstractMap
|
+--java.util.TreeMap
- public class TreeMap
- extends AbstractMap
- implements SortedMap, Cloneable, Serializable
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 Class (see Comparable), or
by the Comparator provided at TreeMap 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 TreeMap (whether or not an
explicit Comparator is provided) must be total if the TreeMap is
to correctly implement the Map interface. (See Comparable or Comparator
for a definition of total ordering.) This is so because the Map
interface is defined in terms of the equals operation, but a TreeMap
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 TreeMap, equal. The behavior of a TreeMap is well-defined
even if its ordering is strictly partial; it just fails to obey the
general contract of the Map interface.
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.synchronizedMap
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
,
Hashtable
,
Comparable
,
Comparator
,
Collection
,
Collections.synchronizedMap(Map)
, Serialized Form
Constructor Summary
|
TreeMap()
Constructs a new, empty TreeMap, sorted according to the keys'
natural order. |
TreeMap(Comparator c)
Constructs a new, empty TreeMap, sorted according to the given
comparator. |
TreeMap(Map m)
Constructs a new TreeMap containing the same mappings as the given
Map, sorted according to the keys' natural order. |
TreeMap(SortedMap m)
Constructs a new TreeMap containing the same mappings as the given
SortedMap, sorted according to the same ordering. |
Method Summary
|
void
|
clear()
Removes all mappings from this TreeMap. |
Object
|
clone()
Returns a shallow copy of this TreeMap. |
Comparator
|
comparator()
Returns the comparator used to order this TreeMap, or null if this
TreeMap uses its keys' natural order. |
boolean
|
containsKey(Object key)
Returns true if this TreeMap 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 SortedMap. |
Object
|
get(Object key)
Returns the value to which this TreeMap maps the specified key.
|
SortedMap
|
headMap(Object toKey)
Returns a view of the portion of this TreeMap whose keys are strictly
less than toKey. |
Set
|
keySet()
Returns a Set view of the keys contained in this TreeMap. |
Object
|
lastKey()
Returns the last (highest) key currently in this SortedMap. |
Object
|
put(Object key,
Object value)
Associates the specified value with the specified key in this TreeMap.
|
void
|
putAll(Map map)
Copies all of the mappings from the specified Map to this TreeMap
These mappings will replace any mappings that this TreeMap had for
any of the keys currently in the specified 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 TreeMap. |
SortedMap
|
subMap(Object fromKey,
Object toKey)
Returns a view of the portion of this TreeMap whose keys range
from fromKey, inclusive, to toKey, exclusive. |
SortedMap
|
tailMap(Object fromKey)
Returns a view of the portion of this TreeMap whose keys are strictly
less than toKey. |
Collection
|
values()
Returns a Collection view of the values contained in this TreeMap.
|
TreeMap
public TreeMap()
- Constructs a new, empty TreeMap, sorted according to the keys'
natural order. 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
TreeMap
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.
TreeMap
public TreeMap(Map m)
- Constructs a new TreeMap containing the same mappings as the given
Map, sorted according to the keys' natural order. 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.
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 TreeMap containing the same mappings as the given
SortedMap, sorted according to the same ordering. This method runs
in linear time.
size
public int size()
- Returns the number of key-value mappings in this TreeMap.
- Returns:
- the number of key-value mappings in this TreeMap.
- Overrides:
- size in class AbstractMap
containsKey
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.- Returns:
- true if this TreeMap contains a mapping for the specified key.
- Throws:
- ClassCastException - key cannot be compared with the keys
currently in the TreeMap.
- NullPointerException - key is null and this TreeMap uses
natural ordering, or its comparator does not tolerate
null keys.
- Overrides:
- containsKey in class AbstractMap
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.
- Parameters:
value
- value whose presence in this Map is to be tested.- Overrides:
- containsValue in class AbstractMap
- Since:
- JDK1.2
get
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.- Returns:
- the value to which this TreeMap maps the specified key, or
null if the TreeMap contains no mapping for the key.
- Throws:
- ClassCastException - key cannot be compared with the keys
currently in the TreeMap.
- NullPointerException - key is null and this TreeMap uses
natural ordering, or its comparator does not tolerate
null keys.
- Overrides:
- get in class AbstractMap
- See Also:
containsKey(Object)
comparator
public Comparator comparator()
- Returns the comparator used to order this TreeMap, or null if this
TreeMap uses its keys' natural order.
- Specified by:
- comparator in interface SortedMap
- Returns:
- the Comparator associated with this SortedMap, or null
if it uses its keys' natural sort method.
firstKey
public Object firstKey()
- Returns the first (lowest) key currently in this SortedMap.
- Specified by:
- firstKey in interface SortedMap
- Returns:
- the first (lowest) key currently in this SortedMap.
- Throws:
- NoSuchElementException - Map is empty.
lastKey
public Object lastKey()
- Returns the last (highest) key currently in this SortedMap.
- Specified by:
- lastKey in interface SortedMap
- Returns:
- the last (highest) key currently in this SortedMap.
- Throws:
- NoSuchElementException - Map is empty.
putAll
public void putAll(Map map)
- Copies all of the mappings from the specified Map to this TreeMap
These mappings will replace any mappings that this TreeMap had for
any of the keys currently in the specified Map.
- 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
or values, and the specified key or value is null.
- Overrides:
- putAll in class AbstractMap
put
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.
- NullPointerException - key is null and this TreeMap uses
natural order, or its comparator does not tolerate
null keys.
- Overrides:
- put in class AbstractMap
remove
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.
- NullPointerException - key is null and this TreeMap uses
natural order, or its comparator does not tolerate
null keys.
- Overrides:
- remove in class AbstractMap
clear
public void clear()
- Removes all mappings from this TreeMap.
- Overrides:
- clear in class AbstractMap
clone
public Object clone()
- Returns a shallow copy of this TreeMap. (The keys and values themselves
are not cloned.)
- Returns:
- a shallow copy of this TreeMap.
- Overrides:
- clone in class Object
keySet
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.
- Returns:
- a Set view of the keys contained in this TreeMap.
- Overrides:
- keySet in class AbstractMap
values
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.
- Returns:
- a Collection view of the values contained in this TreeMap.
- Overrides:
- values in class AbstractMap
entrySet
public Set entrySet()
- Returns a Set view of the mappings contained in this Map. The Set's
Iterator will return the mappings in ascending Key order. Each element
in the returned set is a Map.Entry. 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.
- Returns:
- a Set view of the mappings contained in this Map.
- Overrides:
- entrySet in class AbstractMap
- See Also:
Map.Entry
subMap
public SortedMap 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.
The 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 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:
Map sub = m.subMap(low, high+"\0");
A similarly 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:
Map sub = m.subMap(low+"\0", high);
- Specified by:
- subMap in interface SortedMap
- Parameters:
fromKey
- low endpoint (inclusive) of the subMap.
toKey
- high endpoint (exclusive) of the subMap.- Returns:
- a view of the portion of this TreeMap whose keys range
from fromKey, inclusive, to toKey, exclusive.
- Throws:
- NullPointerException - fromKey or toKey is null and this
TreeMap uses natural order, or its comparator does
not tolerate null keys.
- IllegalArgumentException - fromKey is greater than toKey.
headMap
public SortedMap headMap(Object toKey)
- Returns a view of the portion of this TreeMap whose keys are strictly
less than toKey. 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.
The 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 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:
Map head = m.headMap(high+"\0");
- Specified by:
- headMap in interface SortedMap
- Parameters:
toKey
- high endpoint (exclusive) of the headMap.- Returns:
- a view of the portion of this TreeMap whose keys are strictly
less than toKey.
- Throws:
- NullPointerException - toKey is null and this
TreeMap 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 TreeMap whose keys are strictly
less than toKey. 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.
The 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 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 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:
Map tail = m.tailMap(low+"\0");
- Specified by:
- tailMap in interface SortedMap
- Parameters:
fromKey
- low endpoint (inclusive) of the tailMap.- Returns:
- a view of the portion of this TreeMap whose keys are strictly
less than toKey.
- Throws:
- NullPointerException - fromKey is null and this
TreeMap uses natural ordering, or its comparator does
not tolerate null keys.
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