TreeSet
public
class
TreeSet
extends AbstractSet<E>
implements
NavigableSet<E>,
Cloneable,
Serializable
java.lang.Object | |||
↳ | java.util.AbstractCollection<E> | ||
↳ | java.util.AbstractSet<E> | ||
↳ | java.util.TreeSet<E> |
A NavigableSet
implementation based on a TreeMap
.
The elements are ordered using their ordering, or by a Comparator
provided at set creation
time, depending on which constructor is used.
This implementation provides guaranteed log(n) time cost for the basic
operations (add
, remove
and contains
).
Note that the ordering maintained by a set (whether or not an explicit
comparator is provided) must be consistent with equals if it is to
correctly implement the Set
interface. (See Comparable
or Comparator
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 TreeSet
instance
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 set, equal. The behavior of a set
is well-defined even if its ordering is inconsistent with equals; it
just fails to obey the general contract of the Set
interface.
Note that this implementation is not synchronized.
If multiple threads access a tree set concurrently, and at least one
of the threads modifies the set, it must be synchronized
externally. This is typically accomplished by synchronizing on some
object that naturally encapsulates the set.
If no such object exists, the set should be "wrapped" using the
Collections.synchronizedSortedSet
method. This is best done at creation time, to prevent accidental
unsynchronized access to the set:
SortedSet s = Collections.synchronizedSortedSet(new TreeSet(...));
The iterators returned by this class's iterator
method are
fail-fast: if the set is modified at any time after the iterator is
created, in any way except through the iterator's own remove
method, the iterator will throw a ConcurrentModificationException
.
Thus, in the face of concurrent modification, the iterator fails quickly
and cleanly, rather than risking arbitrary, non-deterministic behavior at
an undetermined time in the future.
Note that the fail-fast behavior of an iterator cannot be guaranteed
as it is, generally speaking, impossible to make any hard guarantees in the
presence of unsynchronized concurrent modification. Fail-fast iterators
throw ConcurrentModificationException
on a best-effort basis.
Therefore, it would be wrong to write a program that depended on this
exception for its correctness: the fail-fast behavior of iterators
should be used only to detect bugs.
The addFirst
and addLast
methods of this class
throw UnsupportedOperationException
. The encounter order of elements is determined
by the comparison method; therefore, explicit positioning is not supported.
This class is a member of the Java Collections Framework.
Summary
Public constructors | |
---|---|
TreeSet()
Constructs a new, empty tree set, sorted according to the natural ordering of its elements. |
|
TreeSet(Comparator<? super E> comparator)
Constructs a new, empty tree set, sorted according to the specified comparator. |
|
TreeSet(Collection<? extends E> c)
Constructs a new tree set containing the elements in the specified collection, sorted according to the natural ordering of its elements. |
|
TreeSet(SortedSet<E> s)
Constructs a new tree set containing the same elements and using the same ordering as the specified sorted set. |
Public methods | |
---|---|
boolean
|
add(E e)
Adds the specified element to this set if it is not already present. |
boolean
|
addAll(Collection<? extends E> c)
Adds all of the elements in the specified collection to this set. |
void
|
addFirst(E e)
Throws |
void
|
addLast(E e)
Throws |
E
|
ceiling(E e)
Returns the least element in this set greater than or equal to
the given element, or |
void
|
clear()
Removes all of the elements from this set. |
Object
|
clone()
Returns a shallow copy of this |
Comparator<? super E>
|
comparator()
Returns the comparator used to order the elements in this set,
or |
boolean
|
contains(Object o)
Returns |
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
|
first()
Returns the first (lowest) element currently in this set. |
E
|
floor(E e)
Returns the greatest element in this set less than or equal to
the given element, or |
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 |
SortedSet<E>
|
headSet(E toElement)
Returns a view of the portion of this set whose elements are
strictly less than Equivalent to |
E
|
higher(E e)
Returns the least element in this set strictly greater than the
given element, or |
boolean
|
isEmpty()
Returns |
Iterator<E>
|
iterator()
Returns an iterator over the elements in this set in ascending order. |
E
|
last()
Returns the last (highest) element currently in this set. |
E
|
lower(E e)
Returns the greatest element in this set strictly less than the
given element, or |
E
|
pollFirst()
Retrieves and removes the first (lowest) element,
or returns |
E
|
pollLast()
Retrieves and removes the last (highest) element,
or returns |
boolean
|
remove(Object o)
Removes the specified element from this set if it is present. |
int
|
size()
Returns the number of elements in this set (its cardinality). |
Spliterator<E>
|
spliterator()
Creates a late-binding
and fail-fast |
NavigableSet<E>
|
subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive)
Returns a view of the portion of this set whose elements range from
|
SortedSet<E>
|
subSet(E fromElement, E toElement)
Returns a view of the portion of this set whose elements range
from Equivalent to |
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 |
SortedSet<E>
|
tailSet(E fromElement)
Returns a view of the portion of this set whose elements are
greater than or equal to Equivalent to |
Inherited methods | |
---|---|
Public constructors
TreeSet
public TreeSet ()
Constructs a new, empty tree set, sorted according to the
natural ordering of its elements. All elements inserted into
the set must implement the Comparable
interface.
Furthermore, all such elements must be mutually
comparable: e1.compareTo(e2)
must not throw a
ClassCastException
for any elements e1
and
e2
in the set. If the user attempts to add an element
to the set that violates this constraint (for example, the user
attempts to add a string element to a set whose elements are
integers), the add
call will throw a
ClassCastException
.
TreeSet
public TreeSet (Comparator<? super E> comparator)
Constructs a new, empty tree set, sorted according to the specified
comparator. All elements inserted into the set must be mutually
comparable by the specified comparator: comparator.compare(e1,
e2)
must not throw a ClassCastException
for any elements
e1
and e2
in the set. If the user attempts to add
an element to the set that violates this constraint, the
add
call will throw a ClassCastException
.
Parameters | |
---|---|
comparator |
Comparator : the comparator that will be used to order this set.
If null , the ordering of the elements will be used. |
TreeSet
public TreeSet (Collection<? extends E> c)
Constructs a new tree set containing the elements in the specified
collection, sorted according to the natural ordering of its
elements. All elements inserted into the set must implement the
Comparable
interface. Furthermore, all such elements must be
mutually comparable: e1.compareTo(e2)
must not throw a
ClassCastException
for any elements e1
and
e2
in the set.
Parameters | |
---|---|
c |
Collection : collection whose elements will comprise the new set |
Throws | |
---|---|
ClassCastException |
if the elements in c are
not Comparable , or are not mutually comparable |
NullPointerException |
if the specified collection is null |
TreeSet
public TreeSet (SortedSet<E> s)
Constructs a new tree set containing the same elements and using the same ordering as the specified sorted set.
Parameters | |
---|---|
s |
SortedSet : sorted set whose elements will comprise the new set |
Throws | |
---|---|
NullPointerException |
if the specified sorted set is null |
Public methods
add
public boolean add (E e)
Adds the specified element to this set if it is not already present.
More formally, adds the specified element e
to this set if
the set contains no element e2
such that
Objects.equals(e, e2)
.
If this set already contains the element, the call leaves the set
unchanged and returns false
.
Parameters | |
---|---|
e |
E : element to be added to this set |
Returns | |
---|---|
boolean |
true if this set did not already contain the specified
element |
Throws | |
---|---|
ClassCastException |
if the specified object cannot be compared with the elements currently in this set |
NullPointerException |
if the specified element is null and this set uses natural ordering, or its comparator does not permit null elements |
addAll
public boolean addAll (Collection<? extends E> c)
Adds all of the elements in the specified collection to this set.
Parameters | |
---|---|
c |
Collection : collection containing elements to be added to this set |
Returns | |
---|---|
boolean |
true if this set changed as a result of the call |
Throws | |
---|---|
ClassCastException |
if the elements provided cannot be compared with the elements currently in the set |
NullPointerException |
if the specified collection is null or if any element is null and this set uses natural ordering, or its comparator does not permit null elements |
addFirst
public void addFirst (E e)
Throws UnsupportedOperationException
. The encounter order induced by this
set's comparison method determines the position of elements, so explicit positioning
is not supported.
Parameters | |
---|---|
e |
E : the element to be added |
Throws | |
---|---|
UnsupportedOperationException |
always |
addLast
public void addLast (E e)
Throws UnsupportedOperationException
. The encounter order induced by this
set's comparison method determines the position of elements, so explicit positioning
is not supported.
Parameters | |
---|---|
e |
E : the element to be added. |
Throws | |
---|---|
UnsupportedOperationException |
always |
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.
Parameters | |
---|---|
e |
E : the value to match |
Returns | |
---|---|
E |
the least element greater than or equal to e ,
or null if there is no such element |
Throws | |
---|---|
ClassCastException |
|
NullPointerException |
if the specified element is null and this set uses natural ordering, or its comparator does not permit null elements |
clear
public void clear ()
Removes all of the elements from this set. The set will be empty after this call returns.
clone
public Object clone ()
Returns a shallow copy of this TreeSet
instance. (The elements
themselves are not cloned.)
Returns | |
---|---|
Object |
a shallow copy of this set |
comparator
public Comparator<? super E> comparator ()
Returns the comparator used to order the elements in this set,
or null
if this set uses the natural ordering of its elements.
Returns | |
---|---|
Comparator<? super E> |
the comparator used to order the elements in this set,
or null if this set uses the natural ordering
of its elements |
contains
public boolean contains (Object o)
Returns true
if this set contains the specified element.
More formally, returns true
if and only if this set
contains an element e
such that
Objects.equals(o, e)
.
Parameters | |
---|---|
o |
Object : object to be checked for containment in this set |
Returns | |
---|---|
boolean |
true if this set contains the specified element |
Throws | |
---|---|
ClassCastException |
if the specified object cannot be compared with the elements currently in the set |
NullPointerException |
if the specified element is null and this set uses natural ordering, or its comparator does not permit null elements |
descendingIterator
public Iterator<E> descendingIterator ()
Returns an iterator over the elements in this set in descending order.
Returns | |
---|---|
Iterator<E> |
an iterator over the elements in this set in descending order |
descendingSet
public NavigableSet<E> 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
.
Returns | |
---|---|
NavigableSet<E> |
a reverse order view of this set |
first
public E first ()
Returns the first (lowest) element currently in this set.
Returns | |
---|---|
E |
the first (lowest) element currently in this set |
Throws | |
---|---|
NoSuchElementException |
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.
Parameters | |
---|---|
e |
E : the value to match |
Returns | |
---|---|
E |
the greatest element less than or equal to e ,
or null if there is no such element |
Throws | |
---|---|
ClassCastException |
|
NullPointerException |
if the specified element is null and this set uses natural ordering, or its comparator does not permit null elements |
headSet
public 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
. 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.
Parameters | |
---|---|
toElement |
E : high endpoint of the returned set |
inclusive |
boolean : true if the high endpoint
is to be included in the returned view |
Returns | |
---|---|
NavigableSet<E> |
a view of the portion of this set whose elements are less than
(or equal to, if inclusive is true) toElement |
Throws | |
---|---|
ClassCastException |
|
NullPointerException |
if toElement is null and
this set uses natural ordering, or its comparator does
not permit null elements |
IllegalArgumentException |
headSet
public SortedSet<E> headSet (E toElement)
Returns a view of the portion of this set whose elements are
strictly less than 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.
Equivalent to headSet(toElement, false)
.
Parameters | |
---|---|
toElement |
E : high endpoint (exclusive) of the returned set |
Returns | |
---|---|
SortedSet<E> |
a view of the portion of this set whose elements are strictly
less than toElement |
Throws | |
---|---|
ClassCastException |
|
NullPointerException |
if toElement is null
and this set uses natural ordering, or its comparator does
not permit null elements |
IllegalArgumentException |
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.
Parameters | |
---|---|
e |
E : the value to match |
Returns | |
---|---|
E |
the least element greater than e ,
or null if there is no such element |
Throws | |
---|---|
ClassCastException |
|
NullPointerException |
if the specified element is null and this set uses natural ordering, or its comparator does not permit null elements |
isEmpty
public boolean isEmpty ()
Returns true
if this set contains no elements.
Returns | |
---|---|
boolean |
true if this set contains no elements |
iterator
public Iterator<E> iterator ()
Returns an iterator over the elements in this set in ascending order.
Returns | |
---|---|
Iterator<E> |
an iterator over the elements in this set in ascending order |
last
public E last ()
Returns the last (highest) element currently in this set.
Returns | |
---|---|
E |
the last (highest) element currently in this set |
Throws | |
---|---|
NoSuchElementException |
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.
Parameters | |
---|---|
e |
E : the value to match |
Returns | |
---|---|
E |
the greatest element less than e ,
or null if there is no such element |
Throws | |
---|---|
ClassCastException |
|
NullPointerException |
if the specified element is null and this set uses natural ordering, or its comparator does not permit null elements |
pollFirst
public E pollFirst ()
Retrieves and removes the first (lowest) element,
or returns null
if this set is empty.
Returns | |
---|---|
E |
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.
Returns | |
---|---|
E |
the last element, or null if this set is empty |
remove
public boolean remove (Object o)
Removes the specified element from this set if it is present.
More formally, removes an element e
such that
Objects.equals(o, e)
,
if this set contains such an element. Returns true
if
this set contained the element (or equivalently, if this set
changed as a result of the call). (This set will not contain the
element once the call returns.)
Parameters | |
---|---|
o |
Object : object to be removed from this set, if present |
Returns | |
---|---|
boolean |
true if this set contained the specified element |
Throws | |
---|---|
ClassCastException |
if the specified object cannot be compared with the elements currently in this set |
NullPointerException |
if the specified element is null and this set uses natural ordering, or its comparator does not permit null elements |
size
public int size ()
Returns the number of elements in this set (its cardinality).
Returns | |
---|---|
int |
the number of elements in this set (its cardinality) |
spliterator
public Spliterator<E> spliterator ()
Creates a late-binding
and fail-fast Spliterator
over the elements in this
set.
The Spliterator
reports Spliterator#SIZED
,
Spliterator#DISTINCT
, Spliterator#SORTED
, and
Spliterator#ORDERED
. Overriding implementations should document
the reporting of additional characteristic values.
The spliterator's comparator (see
Spliterator.getComparator()
) is null
if
the tree set's comparator (see comparator()
) is null
.
Otherwise, the spliterator's comparator is the same as or imposes the
same total ordering as the tree set's comparator.
Returns | |
---|---|
Spliterator<E> |
a Spliterator over the elements in this set |
subSet
public 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
. 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 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.
Parameters | |
---|---|
fromElement |
E : low endpoint of the returned set |
fromInclusive |
boolean : true if the low endpoint
is to be included in the returned view |
toElement |
E : high endpoint of the returned set |
toInclusive |
boolean : true if the high endpoint
is to be included in the returned view |
Returns | |
---|---|
NavigableSet<E> |
a view of the portion of this set whose elements range from
fromElement , inclusive, to toElement , exclusive |
Throws | |
---|---|
ClassCastException |
|
NullPointerException |
if fromElement or toElement
is null and this set uses natural ordering, or its comparator
does not permit null elements |
IllegalArgumentException |
subSet
public 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. (If fromElement
and toElement
are
equal, the returned set is empty.) 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.
Equivalent to subSet(fromElement, true, toElement, false)
.
Parameters | |
---|---|
fromElement |
E : low endpoint (inclusive) of the returned set |
toElement |
E : high endpoint (exclusive) of the returned set |
Returns | |
---|---|
SortedSet<E> |
a view of the portion of this set whose elements range from
fromElement , inclusive, to toElement , exclusive |
Throws | |
---|---|
ClassCastException |
|
NullPointerException |
if fromElement or
toElement is null and this set uses natural ordering,
or its comparator does not permit null elements |
IllegalArgumentException |
tailSet
public 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
.
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.
Parameters | |
---|---|
fromElement |
E : low endpoint of the returned set |
inclusive |
boolean : true if the low endpoint
is to be included in the returned view |
Returns | |
---|---|
NavigableSet<E> |
a view of the portion of this set whose elements are greater
than or equal to fromElement |
Throws | |
---|---|
ClassCastException |
|
NullPointerException |
if fromElement is null and
this set uses natural ordering, or its comparator does
not permit null elements |
IllegalArgumentException |
tailSet
public SortedSet<E> tailSet (E fromElement)
Returns a view of the portion of this set whose elements are
greater than or equal to 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.
Equivalent to tailSet(fromElement, true)
.
Parameters | |
---|---|
fromElement |
E : low endpoint (inclusive) of the returned set |
Returns | |
---|---|
SortedSet<E> |
a view of the portion of this set whose elements are greater
than or equal to fromElement |
Throws | |
---|---|
ClassCastException |
|
NullPointerException |
if fromElement is null
and this set uses natural ordering, or its comparator does
not permit null elements |
IllegalArgumentException |