A
java.util.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
java.lang.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 Object ceiling(Object 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
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 Object floor(Object 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
headSet
public SortedSet headSet(Object toElement)
Equivalent to headSet(toElement, false)
.
headSet
public NavigableSet headSet(Object 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
higher
public Object higher(Object 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
iterator
public Iterator iterator()
Returns an iterator over the elements in this set, in ascending order.
- an iterator over the elements in this set, in ascending order
lower
public Object lower(Object 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
pollFirst
public Object 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 Object 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(Object fromElement,
Object toElement)
Equivalent to subSet(fromElement, true, toElement, false)
.
subSet
public NavigableSet subSet(Object fromElement,
boolean fromInclusive,
Object 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
tailSet
public SortedSet tailSet(Object fromElement)
Equivalent to tailSet(fromElement, true)
.
tailSet
public NavigableSet tailSet(Object 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