E
 the type of elements maintained by this setpublic interface NavigableSet<E> extends SortedSet<E>
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 likenamed 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 Java Collections Framework.
Modifier and Type  Method and Description 

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. 
java.util.Iterator<E> 
descendingIterator()
Returns an iterator over the elements in this set, in descending order.

NavigableSet<E> 
descendingSet()
Returns a reverse order view of the elements contained in this set.

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. 
SortedSet<E> 
headSet(E toElement)
Returns a view of the portion of this set whose elements are
strictly less than toElement.

NavigableSet<E> 
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 . 
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. 
java.util.Iterator<E> 
iterator()
Returns an iterator over the elements in this set, in ascending order.

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. 
E 
pollFirst()
Retrieves and removes the first (lowest) element,
or returns
null if this set is empty. 
E 
pollLast()
Retrieves and removes the last (highest) element,
or returns
null if this set is empty. 
NavigableSet<E> 
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 . 
SortedSet<E> 
subSet(E fromElement,
E toElement)
Returns a view of the portion of this set whose elements range
from fromElement, inclusive, to toElement,
exclusive.

SortedSet<E> 
tailSet(E fromElement)
Returns a view of the portion of this set whose elements are
greater than or equal to fromElement.

NavigableSet<E> 
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 . 
comparator, first, last
E lower(E e)
null
if there is no such element.e
 the value to matche
,
or null
if there is no such elementjava.lang.ClassCastException
 if the specified element cannot be
compared with the elements currently in the setjava.lang.NullPointerException
 if the specified element is null
and this set does not permit null elementsE floor(E e)
null
if there is no such element.e
 the value to matche
,
or null
if there is no such elementjava.lang.ClassCastException
 if the specified element cannot be
compared with the elements currently in the setjava.lang.NullPointerException
 if the specified element is null
and this set does not permit null elementsE ceiling(E e)
null
if there is no such element.e
 the value to matche
,
or null
if there is no such elementjava.lang.ClassCastException
 if the specified element cannot be
compared with the elements currently in the setjava.lang.NullPointerException
 if the specified element is null
and this set does not permit null elementsE higher(E e)
null
if there is no such element.e
 the value to matche
,
or null
if there is no such elementjava.lang.ClassCastException
 if the specified element cannot be
compared with the elements currently in the setjava.lang.NullPointerException
 if the specified element is null
and this set does not permit null elementsE pollFirst()
null
if this set is empty.null
if this set is emptyE pollLast()
null
if this set is empty.null
if this set is emptyjava.util.Iterator<E> iterator()
NavigableSet<E> descendingSet()
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
.
java.util.Iterator<E> descendingIterator()
descendingSet().iterator()
.NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive)
fromElement
to toElement
. If fromElement
and
toElement
are equal, the returned set is empty unless fromInclusive
and toInclusive
are both true. The returned set
is backed by this set, so changes in the returned set are reflected in
this set, and viceversa. 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 viewfromElement
, inclusive, to toElement
, exclusivejava.lang.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.java.lang.NullPointerException
 if fromElement
or
toElement
is null and this set does
not permit null elementsjava.lang.IllegalArgumentException
 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.NavigableSet<E> headSet(E toElement, boolean inclusive)
inclusive
is true) toElement
. The
returned set is backed by this set, so changes in the returned set are
reflected in this set, and viceversa. 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 viewinclusive
is true) toElement
java.lang.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.java.lang.NullPointerException
 if toElement
is null and
this set does not permit null elementsjava.lang.IllegalArgumentException
 if this set itself has a
restricted range, and toElement
lies outside the
bounds of the rangeNavigableSet<E> tailSet(E fromElement, boolean inclusive)
inclusive
is true) fromElement
.
The returned set is backed by this set, so changes in the returned set
are reflected in this set, and viceversa. 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 viewfromElement
java.lang.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.java.lang.NullPointerException
 if fromElement
is null
and this set does not permit null elementsjava.lang.IllegalArgumentException
 if this set itself has a
restricted range, and fromElement
lies outside the
bounds of the rangeSortedSet<E> subSet(E fromElement, E toElement)
The returned set will throw an IllegalArgumentException on an attempt to insert an element outside its range.
Equivalent to subSet(fromElement, true, toElement, false)
.
subSet
in interface SortedSet<E>
fromElement
 low endpoint (inclusive) of the returned settoElement
 high endpoint (exclusive) of the returned setjava.lang.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.java.lang.NullPointerException
 if fromElement or
toElement is null and this set does not permit null
elementsjava.lang.IllegalArgumentException
 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 rangeSortedSet<E> headSet(E toElement)
The returned set will throw an IllegalArgumentException on an attempt to insert an element outside its range.
Equivalent to headSet(toElement, false)
.
headSet
in interface SortedSet<E>
toElement
 high endpoint (exclusive) of the returned setjava.lang.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.java.lang.NullPointerException
 if toElement is null and
this set does not permit null elementsjava.lang.IllegalArgumentException
 if this set itself has a
restricted range, and toElement lies outside the
bounds of the rangeSortedSet<E> tailSet(E fromElement)
The returned set will throw an IllegalArgumentException on an attempt to insert an element outside its range.
Equivalent to tailSet(fromElement, true)
.
tailSet
in interface SortedSet<E>
fromElement
 low endpoint (inclusive) of the returned setjava.lang.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.java.lang.NullPointerException
 if fromElement is null
and this set does not permit null elementsjava.lang.IllegalArgumentException
 if this set itself has a
restricted range, and fromElement lies outside the
bounds of the range