java.util

Interface SortedSet

All Superinterfaces:

Collection, Set

All Known Implementing Classes:

TreeSet

public interface SortedSet
extends Set

A set that further guarantees that its iterator will traverse the set in ascending element order, sorted according to the natural ordering of its elements (see Comparable), or by a Comparator provided at sorted set creation time. Several additional operations are provided to take advantage of the ordering. (This interface is the set analogue of SortedMap.)

All elements inserted into an sorted set must implement the Comparable interface (or be accepted by the specified Comparator). Furthermore, all such elements must be mutually comparable: e1.compareTo(e2) (or comparator.compare(e1, e2)) must not throw a ClassCastException for any elements e1 and e2 in the sorted set. 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 set (whether or not an explicit comparator is provided) must be consistent with equals if the sorted set is to correctly implement the Set interface. (See the Comparable interface or Comparator interface for a precise definition of consistent with equals.) This is so because the Set interface is defined in terms of the equals operation, but a sorted set performs all element comparisons using its compareTo (or compare) method, so two elements that are deemed equal by this method are, from the standpoint of the sorted set, equal. The behavior of a sorted set is well-defined even if its ordering is inconsistent with equals; it just fails to obey the general contract of the Set interface.

All general-purpose sorted set implementation classes should provide four "standard" constructors: 1) A void (no arguments) constructor, which creates an empty sorted set sorted according to the natural order of its elements. 2) A constructor with a single argument of type Comparator, which creates an empty sorted set sorted according to the specified comparator. 3) A constructor with a single argument of type Collection, which creates a new sorted set with the same elements as its argument, sorted according to the elements' natural ordering. 4) A constructor with a single argument of type SortedSet, which creates a new sorted set with the same elements and the same ordering as the input sorted set. There is no way to enforce this recommendation (as interfaces cannot contain constructors) but the SDK implementation (the TreeSet class) complies.

This interface is a member of the Java Collections Framework.

Since:

1.2

Version:

1.15, 02/02/00

Author:

Josh Bloch

See Also:

Set, TreeSet, SortedMap, Collection, Comparable, Comparator, ClassCastException

Method Summary

Methods

Modifier and Type	Method and Description
Comparator	comparator() Returns the comparator associated with this sorted set, or null if it uses its elements' natural ordering.
Object	first() Returns the first (lowest) element currently in this sorted set.
SortedSet	headSet(Object toElement) Returns a view of the portion of this sorted set whose elements are strictly less than toElement.
Object	last() Returns the last (highest) element currently in this sorted set.
SortedSet	subSet(Object fromElement, Object toElement) Returns a view of the portion of this sorted set whose elements range from fromElement, inclusive, to toElement, exclusive.
SortedSet	tailSet(Object fromElement) Returns a view of the portion of this sorted set whose elements are greater than or equal to fromElement.

Methods inherited from interface java.util.Set

add, addAll, clear, contains, containsAll, equals, hashCode, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toArray

Method Detail

comparator

Comparator comparator()

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

Returns:

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

subSet

SortedSet subSet(Object fromElement,
               Object toElement)

Returns a view of the portion of this sorted set whose elements range from fromElement, inclusive, to toElement, exclusive. (If fromElement and toElement are equal, the returned sorted set is empty.) The returned sorted set is backed by this sorted set, so changes in the returned sorted set are reflected in this sorted set, and vice-versa. The returned sorted set supports all optional set operations that this sorted set supports.

The sorted set returned by this method will throw an IllegalArgumentException if the user attempts to insert a element 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 element type allows for calculation of the successor a given value, merely request the subrange from lowEndpoint to successor(highEndpoint). For example, suppose that s is a sorted set of strings. The following idiom obtains a view containing all of the strings in s from low to high, inclusive:

 SortedSet sub = s.subSet(low, high+"\0");
 

A similar technique can be used to generate an open range (which contains neither endpoint). The following idiom obtains a view containing all of the Strings in s from low to high, exclusive:

 SortedSet sub = s.subSet(low+"\0", high);
 

Parameters:

fromElement - low endpoint (inclusive) of the subSet.

toElement - high endpoint (exclusive) of the subSet.

Returns:

a view of the specified range within this sorted set.

Throws:

ClassCastException - if fromElement and toElement cannot be compared to one another using this set's comparator (or, if the set has no comparator, using natural ordering). Implementations may, but are not required to, throw this exception if fromElement or toElement cannot be compared to elements currently in the set.

IllegalArgumentException - if fromElement is greater than toElement; or if this set is itself a subSet, headSet, or tailSet, and fromElement or toElement are not within the specified range of the subSet, headSet, or tailSet.

NullPointerException - if fromElement or toElement is null and this sorted set does not tolerate null elements.

headSet

SortedSet headSet(Object toElement)

Returns a view of the portion of this sorted set whose elements are strictly less than toElement. The returned sorted set is backed by this sorted set, so changes in the returned sorted set are reflected in this sorted set, and vice-versa. The returned sorted set supports all optional set operations.

The sorted set returned by this method will throw an IllegalArgumentException if the user attempts to insert a element 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 element type allows for calculation of the successor a given value, merely request a headSet bounded by successor(highEndpoint). For example, suppose that s is a sorted set of strings. The following idiom obtains a view containing all of the strings in s that are less than or equal to high:

    SortedSet head = s.headSet(high+"\0");

Parameters:

toElement - high endpoint (exclusive) of the headSet.

Returns:

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

Throws:

ClassCastException - if toElement is not compatible with this set's comparator (or, if the set has no comparator, if toElement does not implement Comparable). Implementations may, but are not required to, throw this exception if toElement cannot be compared to elements currently in the set.

NullPointerException - if toElement is null and this sorted set does not tolerate null elements.

IllegalArgumentException - if this set is itself a subSet, headSet, or tailSet, and toElement is not within the specified range of the subSet, headSet, or tailSet.

tailSet

SortedSet tailSet(Object fromElement)

Returns a view of the portion of this sorted set whose elements are greater than or equal to fromElement. The returned sorted set is backed by this sorted set, so changes in the returned sorted set are reflected in this sorted set, and vice-versa. The returned sorted set supports all optional set operations.

The sorted set returned by this method will throw an IllegalArgumentException if the user attempts to insert a element 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 tailSet bounded by successor(lowEndpoint). For example, suppose that s is a sorted set of strings. The following idiom obtains a view containing all of the strings in s that are strictly greater than low:

    SortedSet tail = s.tailSet(low+"\0");

Parameters:

fromElement - low endpoint (inclusive) of the tailSet.

Returns:

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

Throws:

ClassCastException - if fromElement is not compatible with this set's comparator (or, if the set has no comparator, if fromElement does not implement Comparable). Implementations may, but are not required to, throw this exception if fromElement cannot be compared to elements currently in the set.

NullPointerException - if fromElement is null and this sorted set does not tolerate null elements.

IllegalArgumentException - if this set is itself a subSet, headSet, or tailSet, and fromElement is not within the specified range of the subSet, headSet, or tailSet.

first

Object first()

Returns the first (lowest) element currently in this sorted set.

Returns:

the first (lowest) element currently in this sorted set.

Throws:

NoSuchElementException - sorted set is empty.

last

Object last()

Returns the last (highest) element currently in this sorted set.

Returns:

the last (highest) element currently in this sorted set.

Throws:

NoSuchElementException - sorted set is empty.