SortedMap (Java 2 Platform SE 5.0) (original) (raw)

java.util

Interface SortedMap<K,V>

All Superinterfaces:

Map<K,V>

All Known Implementing Classes:

TreeMap

public interface SortedMap<K,V>

extends Map<K,V>

A map that further guarantees that it will be in ascending key order, sorted according to the natural ordering of its keys (see theComparable 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) (orcomparator.compare(k1, k2)) must not throw aClassCastException 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 aClassCastException.

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 itscompareTo (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 typeComparator, which creates an empty sorted map sorted according to the specified comparator. 3) A constructor with a single argument of typeMap, 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.

Since:

1.2

See Also:

Map, TreeMap, SortedSet, Comparator, Comparable, Collection, ClassCastException

comparator

Comparator<? super K> comparator()

Returns the comparator associated with this sorted map, ornull if it uses its keys' natural ordering.

Returns:

the comparator associated with this sorted map, ornull if it uses its keys' natural ordering.

subMap

SortedMap<K,V> subMap(K fromKey, K toKey)

Returns a view of the portion of this sorted map whose keys range fromfromKey, inclusive, to toKey, exclusive. (IffromKey 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 anIllegalArgumentException 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 andhigh, 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);

Parameters:

fromKey - low endpoint (inclusive) of the subMap.

toKey - high endpoint (exclusive) of the subMap.

Returns:

a view of the specified range within this sorted map.

Throws:

[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang") - if fromKey and toKey cannot be compared to one another using this map's comparator (or, if the map has no comparator, using natural ordering). Implementations may, but are not required to, throw this exception if fromKey or toKey cannot be compared to keys currently in the map.

[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang") - if fromKey is greater thantoKey; or if this map is itself a subMap, headMap, or tailMap, and fromKey or toKey are not within the specified range of the subMap, headMap, or tailMap.

[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if fromKey or toKey isnull and this sorted map does not toleratenull keys.

headMap

SortedMap<K,V> 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 tohigh:

Map head = m.headMap(high+"\0");

Parameters:

toKey - high endpoint (exclusive) of the subMap.

Returns:

a view of the specified initial range of this sorted map.

Throws:

[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang") - if toKey is not compatible with this map's comparator (or, if the map has no comparator, if toKey does not implement Comparable). Implementations may, but are not required to, throw this exception if toKey cannot be compared to keys currently in the map.

[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang") - if this map is itself a subMap, headMap, or tailMap, and toKey is not within the specified range of the subMap, headMap, or tailMap.

[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if toKey is null and this sorted map does not tolerate null keys.

tailMap

SortedMap<K,V> 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 anIllegalArgumentException 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 thanlow:

Map tail = m.tailMap(low+"\0");

Parameters:

fromKey - low endpoint (inclusive) of the tailMap.

Returns:

a view of the specified final range of this sorted map.

Throws:

[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang") - if fromKey is not compatible with this map's comparator (or, if the map has no comparator, if fromKey does not implement Comparable). Implementations may, but are not required to, throw this exception if fromKey cannot be compared to keys currently in the map.

[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang") - if this map is itself a subMap, headMap, or tailMap, and fromKey is not within the specified range of the subMap, headMap, or tailMap.

[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if fromKey is null and this sorted map does not tolerate null keys.

firstKey

K firstKey()

Returns the first (lowest) key currently in this sorted map.

Returns:

the first (lowest) key currently in this sorted map.

Throws:

[NoSuchElementException](../../java/util/NoSuchElementException.html "class in java.util") - if this map is empty.

lastKey

K lastKey()

Returns the last (highest) key currently in this sorted map.

Returns:

the last (highest) key currently in this sorted map.

Throws:

[NoSuchElementException](../../java/util/NoSuchElementException.html "class in java.util") - if this map is empty.

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For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

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