SortedMappublic interface SortedMap implements Map| A map that further guarantees that it will be in ascending key order,
sorted according to the natural ordering of its keys (see the
Comparable interface), or by a comparator provided at sorted map
creation time. This order is reflected when iterating over the sorted
map's collection views (returned by the entrySet, keySet
and values methods). Several additional operations are provided
to take advantage of the ordering. (This interface is the map analogue of
the SortedSet interface.)
All keys inserted into a sorted map must implement the Comparable
interface (or be accepted by the specified comparator). Furthermore, all
such keys must be mutually comparable: k1.compareTo(k2) (or
comparator.compare(k1, k2)) must not throw a
ClassCastException for any elements k1 and k2 in
the sorted map. Attempts to violate this restriction will cause the
offending method or constructor invocation to throw a
ClassCastException.
Note that the ordering maintained by a sorted map (whether or not an
explicit comparator is provided) must be consistent with equals if
the sorted map is to correctly implement the Map interface. (See
the Comparable interface or Comparator interface 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 sorted 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 tree map is well-defined even if its
ordering is inconsistent with equals; it just fails to obey the general
contract of the Map interface.
All general-purpose sorted map implementation classes should provide four
"standard" constructors: 1) A void (no arguments) constructor, which
creates an empty sorted map sorted according to the natural order of
its keys. 2) A constructor with a single argument of type
Comparator, which creates an empty sorted map sorted according to
the specified comparator. 3) A constructor with a single argument of type
Map, which creates a new map with the same key-value mappings as
its argument, sorted according to the keys' natural ordering. 4) A
constructor with a single argument of type sorted map, which creates a new
sorted map with the same key-value mappings and the same ordering as the
input sorted map. There is no way to enforce this recommendation (as
interfaces cannot contain constructors) but the JDK implementation
(TreeMap) complies.
This interface is a member of the
Java Collections Framework. |
| Methods Summary |
|---|
| public java.util.Comparator | comparator()Returns the comparator associated with this sorted map, or
null if it uses its keys' natural ordering.
| | public K | firstKey()Returns the first (lowest) key currently in this sorted map.
| | public java.util.SortedMap | headMap(K toKey)Returns a view of the portion of this sorted map whose keys are
strictly less than toKey. The returned sorted map is backed by this
sorted map, so changes in the returned sorted map are reflected in this
sorted map, and vice-versa. The returned map supports all optional map
operations that this sorted map supports.
The map returned by this method will throw an IllegalArgumentException
if the user attempts to insert a key outside the specified range.
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");
| | public K | lastKey()Returns the last (highest) key currently in this sorted map.
| | public java.util.SortedMap | subMap(K fromKey, K toKey)Returns a view of the portion of this sorted 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 sorted map, so
changes in the returned sorted map are reflected in this sorted map,
and vice-versa. The returned Map supports all optional map operations
that this sorted map supports.
The map returned by this method will throw an
IllegalArgumentException if the user attempts to insert a key
outside the specified range.
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);
| | public java.util.SortedMap | tailMap(K fromKey)Returns a view of the portion of this sorted map whose keys are greater
than or equal to fromKey. The returned sorted map is backed
by this sorted map, so changes in the returned sorted map are reflected
in this sorted map, and vice-versa. The returned map supports all
optional map operations that this sorted map supports.
The map returned by this method will throw an
IllegalArgumentException if the user attempts to insert a key
outside the specified range.
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 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");
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