A
SortedSet
extended with navigation methods reporting
closest matches for given search targets. Methods
lower
,
floor
,
ceiling
, and
higher
return elements
respectively less than, less than or equal, greater than or equal,
and greater than a given element, returning
null
if there
is no such element. A
NavigableSet
may be accessed and
traversed in either ascending or descending order. The
descendingSet
method returns a view of the set with the senses of
all relational and directional methods inverted. The performance of
ascending operations and views is likely to be faster than that of
descending ones. This interface additionally defines methods
pollFirst
and
pollLast
that return and remove the
lowest and highest element, if one exists, else returning
null
. Methods
subSet
,
headSet
,
and
tailSet
differ from the like-named
SortedSet
methods in accepting additional arguments describing
whether lower and upper bounds are inclusive versus exclusive.
Subsets of any
NavigableSet
must implement the
NavigableSet
interface.
The return values of navigation methods may be ambiguous in
implementations that permit
null
elements. However, even
in this case the result can be disambiguated by checking
contains(null)
. To avoid such issues, implementations of
this interface are encouraged to
not permit insertion of
null
elements. (Note that sorted sets of
Comparable
elements intrinsically do not permit
null
.)
Methods
subSet(E, E)
,
headSet(E)
, and
tailSet(E)
are specified to return
SortedSet
to allow existing
implementations of
SortedSet
to be compatibly retrofitted to
implement
NavigableSet
, but extensions and implementations
of this interface are encouraged to override these methods to return
NavigableSet
.
This interface is a member of the
../../../technotes/guides/collections/index.html">
Java Collections Framework.
ceiling
public E ceiling(E e)
Returns the least element in this set greater than or equal to
the given element, or null
if there is no such element.
- the least element greater than or equal to
e
,
or null
if there is no such element
ClassCastException
- if the specified element cannot be
compared with the elements currently in the setNullPointerException
- if the specified element is null
and this set does not permit null elements
descendingIterator
public Iterator descendingIterator()
Returns an iterator over the elements in this set, in descending order.
Equivalent in effect to descendingSet().iterator()
.
- an iterator over the elements in this set, in descending order
descendingSet
public NavigableSet descendingSet()
Returns a reverse order view of the elements contained in this set.
The descending set is backed by this set, so changes to the set are
reflected in the descending set, and vice-versa. If either set is
modified while an iteration over either set is in progress (except
through the iterator's own
remove
operation), the results of
the iteration are undefined.
The returned set has an ordering equivalent to
Collections.reverseOrder
(comparator()).
The expression
s.descendingSet().descendingSet()
returns a
view of
s
essentially equivalent to
s
.
- a reverse order view of this set
floor
public E floor(E e)
Returns the greatest element in this set less than or equal to
the given element, or null
if there is no such element.
- the greatest element less than or equal to
e
,
or null
if there is no such element
ClassCastException
- if the specified element cannot be
compared with the elements currently in the setNullPointerException
- if the specified element is null
and this set does not permit null elements
headSet
public NavigableSet headSet(E toElement,
boolean inclusive)
Returns a view of the portion of this set whose elements are less than
(or equal to, if
inclusive
is true)
toElement
. The
returned set is backed by this set, so changes in the returned set are
reflected in this set, and vice-versa. The returned set supports all
optional set operations that this set supports.
The returned set will throw an
IllegalArgumentException
on an attempt to insert an element outside its range.
toElement
- high endpoint of the returned setinclusive
- true
if the high endpoint
is to be included in the returned view
- a view of the portion of this set whose elements are less than
(or equal to, if
inclusive
is true) toElement
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 set does not permit null elementsIllegalArgumentException
- if this set itself has a
restricted range, and toElement
lies outside the
bounds of the range
higher
public E higher(E e)
Returns the least element in this set strictly greater than the
given element, or null
if there is no such element.
- the least element greater than
e
,
or null
if there is no such element
ClassCastException
- if the specified element cannot be
compared with the elements currently in the setNullPointerException
- if the specified element is null
and this set does not permit null elements
lower
public E lower(E e)
Returns the greatest element in this set strictly less than the
given element, or null
if there is no such element.
- the greatest element less than
e
,
or null
if there is no such element
ClassCastException
- if the specified element cannot be
compared with the elements currently in the setNullPointerException
- if the specified element is null
and this set does not permit null elements
pollFirst
public E pollFirst()
Retrieves and removes the first (lowest) element,
or returns null
if this set is empty.
- the first element, or
null
if this set is empty
pollLast
public E pollLast()
Retrieves and removes the last (highest) element,
or returns null
if this set is empty.
- the last element, or
null
if this set is empty
subSet
public SortedSet subSet(E fromElement,
E toElement)
Equivalent to subSet(fromElement, true, toElement, false)
.
- subSet in interface SortedSet<E>
subSet
public NavigableSet subSet(E fromElement,
boolean fromInclusive,
E toElement,
boolean toInclusive)
Returns a view of the portion of this set whose elements range from
fromElement
to
toElement
. If
fromElement
and
toElement
are equal, the returned set is empty unless
fromExclusive
and
toExclusive
are both true. The returned set
is backed by this set, so changes in the returned set are reflected in
this set, and vice-versa. The returned set supports all optional set
operations that this set supports.
The returned set will throw an
IllegalArgumentException
on an attempt to insert an element outside its range.
fromElement
- low endpoint of the returned setfromInclusive
- true
if the low endpoint
is to be included in the returned viewtoElement
- high endpoint of the returned settoInclusive
- true
if the high endpoint
is to be included in the returned view
- a view of the portion of this set whose elements range from
fromElement
, inclusive, to toElement
, exclusive
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.NullPointerException
- if fromElement
or
toElement
is null and this set does
not permit null elementsIllegalArgumentException
- if fromElement
is
greater than toElement
; or if this set itself
has a restricted range, and fromElement
or
toElement
lies outside the bounds of the range.
tailSet
public NavigableSet tailSet(E fromElement,
boolean inclusive)
Returns a view of the portion of this set whose elements are greater
than (or equal to, if
inclusive
is true)
fromElement
.
The returned set is backed by this set, so changes in the returned set
are reflected in this set, and vice-versa. The returned set supports
all optional set operations that this set supports.
The returned set will throw an
IllegalArgumentException
on an attempt to insert an element outside its range.
fromElement
- low endpoint of the returned setinclusive
- true
if the low endpoint
is to be included in the returned view
- a view of the portion of this set whose elements are greater
than or equal to
fromElement
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 set does not permit null elementsIllegalArgumentException
- if this set itself has a
restricted range, and fromElement
lies outside the
bounds of the range