Overview | Package | Class | Tree | Index | Help
PREV CLASS | NEXT CLASS	FRAMES | NO FRAMES
SUMMARY: INNER | FIELD | CONSTR | METHOD	DETAIL: FIELD | CONSTR | METHOD

Interface java.util.SortedMap

Implementing Classes:

Collections.SynchronizedSortedMap, Collections.UnmodifiableSortedMap, TreeMap

public abstract 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 Comparable), or by a Comparator provided at SortedMap creation time. This order is reflected when iterating over the SortedMap's Collection views. Several additional operations are provided to take advantage of the ordering. (This interface is the Map analogue of SortedSet.)

All keys inserted into an SortedMap 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 typeMismatchException for any elements k1 and k2 in the SortedMap. Attempts to violate this restriction will cause the offending method or constructor invocation to throw a ClassCastException.

Note that the ordering maintained by a SortedMap (whether or not an explicit Comparator is provided) must be total if the SortedMap 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 SortedMap 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 SortedMap, equal. The only JDK class whose natural ordering does not satisfy this constraint is BigDecimal.

All general-purpose SortedMap implementation classes should provide four "standard" constructors: 1) A void (no arguments) constructor, which creates an empty SortedMap sorted according to the natural order of its keys. 2) A constructor with a single argument of type Comparator, which creates an empty SortedMap 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 SortedMap, which creates a new SortedMap with the same key-value mappings and the same ordering as the input SortedMap. There is no way to enforce this recommendation (as interfaces cannot contain constructors) but the JDK implementation (TreeMap) complies.

Since:

JDK1.2

Version:

1.5 06/29/98

See Also:

Map, TreeMap, SortedSet, Comparator, java.lang.Comparable, Collection, ClassCastException

Method Summary

Comparator	comparator() Returns the Comparator associated with this SortedMap, or null if it uses its keys' natural ordering.
java.lang.Object	firstKey() Returns the first (lowest) key currently in this SortedMap.
SortedMap	headMap(java.lang.Object toKey) Returns a view of the portion of this SortedMap whose keys are strictly less than toKey.
java.lang.Object	lastKey() Returns the last (highest) key currently in this SortedMap.
SortedMap	subMap(java.lang.Object fromKey, java.lang.Object toKey) Returns a view of the portion of this SortedMap whose keys range from fromKey, inclusive, to toKey, exclusive.
SortedMap	tailMap(java.lang.Object fromKey) Returns a view of the portion of this SortedMap whose keys are greater than or equal to fromKey.

Method Detail

comparator

public Comparator comparator()

Returns the Comparator associated with this SortedMap, or null if it uses its keys' natural ordering.

Returns:

the Comparator associated with this SortedMap, or null if it uses its keys' natural ordering.

subMap

public SortedMap subMap(java.lang.Object fromKey,
                        java.lang.Object toKey)

Returns a view of the portion of this SortedMap whose keys range from fromKey, inclusive, to toKey, exclusive. The returned SortedMap is backed by this SortedMap, so changes in the returned SortedMap are reflected in this SortedMap, 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 outside the specified range.

Parameters:

fromKey - low endpoint (inclusive) of the subMap.

toKey - high endpoint (exclusive) of the subMap.

Returns:

a view of the specified range within this SortedMap.

Throws:

ClassCastException - fromKey or toKey cannot be compared with the keys currently in the SortedMap.

NullPointerException - fromKey or toKey is null and this SortedMap does not tolerate null keys.

java.lang.IllegalArgumentException - fromKey is greater than toKey.

headMap

public SortedMap headMap(java.lang.Object toKey)

Returns a view of the portion of this SortedMap whose keys are strictly less than toKey. The returned SortedMap is backed by this SortedMap, so changes in the returned SortedMap are reflected in this SortedMap, 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 outside the specified range.

Parameters:

toKey - high endpoint (exclusive) of the subMap.

Returns:

a view of the specified initial range of this SortedMap.

Throws:

ClassCastException - toKey cannot be compared with the keys currently in the SortedMap.

NullPointerException - toKey is null and this SortedMap does not tolerate null keys.

tailMap

public SortedMap tailMap(java.lang.Object fromKey)

Returns a view of the portion of this SortedMap whose keys are greater than or equal to fromKey. The returned SortedMap is backed by this SortedMap, so changes in the returned SortedMap are reflected in this SortedMap, 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 outside the specified range.

Parameters:

toKey - high endpoint (exclusive) of the subMap.

Returns:

a view of the specified final range of this SortedMap.

Throws:

ClassCastException - toKey cannot be compared with the keys currently in the SortedMap.

NullPointerException - fromKey is null and this SortedMap does not tolerate null keys.

firstKey

public java.lang.Object firstKey()

Returns the first (lowest) key currently in this SortedMap.

Returns:

the first (lowest) key currently in this SortedMap.

Throws:

IllegalStateException - Map is empty.

lastKey

public java.lang.Object lastKey()

Returns the last (highest) key currently in this SortedMap.

Returns:

the last (highest) key currently in this SortedMap.

Throws:

IllegalStateException - Map is empty.