java.util
Interface SortedMap

All Superinterfaces:

Map

All Known Implementing Classes:

Collections.SynchronizedSortedMap, Collections.UnmodifiableSortedMap, TreeMap, TreeMap.SubMap

public interface SortedMap

extends 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 SDK implementation (TreeMap) complies.

This interface is a member of the Java Collections Framework.

Since:

1.2

Author:

Josh Bloch

See Also:

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

Nested Class Summary

Nested 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

comparator

public Comparator comparator()

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

Returns:

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

subMap

public 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. (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);

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 - 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 - if fromKey is greater than toKey; 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 - if fromKey or toKey is null and this sorted map does not tolerate null keys.

headMap

public SortedMap headMap(Object 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");

Parameters:

toKey - high endpoint (exclusive) of the subMap.

Returns:

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

Throws:

ClassCastException - 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 - 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 - if toKey is null and this sorted map does not tolerate null keys.

tailMap

public SortedMap tailMap(Object 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");

Parameters:

fromKey - low endpoint (inclusive) of the tailMap.

Returns:

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

Throws:

ClassCastException - 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 - 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 - if fromKey is null and this sorted map does not tolerate null keys.

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 - if this 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 - if this map is empty.