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## 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.

Since:
  1.2
See Also:
  `Set`, `TreeSet`, `SortedMap`, `Collection`, `Comparable`, `Comparator`, `ClassCastException`

Method Summary
`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

    public 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

    public 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

    public 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

    public 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

    public 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

    public 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.

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