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Java Platform 1.2 |
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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.
Map,
TreeMap,
SortedSet,
Comparator,
Comparable,
Collection,
ClassCastException| Inner classes inherited from class java.util.Map |
Map.Entry |
| Method Summary | |
Comparator |
comparator()
Returns the comparator associated with this sorted map, or null if it uses its keys' natural ordering. |
Object |
firstKey()
Returns the first (lowest) key currently in this sorted map. |
SortedMap |
headMap(Object toKey)
Returns a view of the portion of this sorted map whose keys are strictly less than toKey. |
Object |
lastKey()
Returns the last (highest) key currently in this sorted map. |
SortedMap |
subMap(Object fromKey,
Object toKey)
Returns a view of the portion of this sorted map whose keys range from fromKey, inclusive, to toKey, exclusive. |
SortedMap |
tailMap(Object fromKey)
Returns a view of the portion of this sorted map whose keys are greater than or equal to fromKey. |
| Methods inherited from interface java.util.Map |
clear,
containsKey,
containsValue,
entrySet,
equals,
get,
hashCode,
isEmpty,
keySet,
put,
putAll,
remove,
size,
values |
| Method Detail |
public Comparator comparator()
public SortedMap subMap(Object fromKey,
Object toKey)
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);
fromKey - low endpoint (inclusive) of the subMap.toKey - high endpoint (exclusive) of the subMap.public SortedMap headMap(Object toKey)
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");
toKey - high endpoint (exclusive) of the subMap.public SortedMap tailMap(Object fromKey)
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");
fromKey - low endpoint (inclusive) of the tailMap.public Object firstKey()
public Object lastKey()
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Java Platform 1.2 |
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