E
- the type of elements maintained by this setSerializable
, Cloneable
, Iterable<E>
, Collection<E>
, NavigableSet<E>
, SequencedCollection<E>
, SequencedSet<E>
, Set<E>
, SortedSet<E>
public class TreeSet<E> extends AbstractSet<E> implements NavigableSet<E>, Cloneable, Serializable
NavigableSet
implementation based on a TreeMap
. The elements are ordered using their natural 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.
Constructor | Description |
---|---|
TreeSet() |
Constructs a new, empty tree set, sorted according to the natural ordering of its elements. |
TreeSet |
Constructs a new tree set containing the elements in the specified collection, sorted according to the natural ordering of its elements. |
TreeSet |
Constructs a new, empty tree set, sorted according to the specified comparator. |
TreeSet |
Constructs a new tree set containing the same elements and using the same ordering as the specified sorted set. |
Modifier and Type | Method | Description |
---|---|---|
boolean |
add |
Adds the specified element to this set if it is not already present. |
boolean |
addAll |
Adds all of the elements in the specified collection to this set. |
void |
addFirst |
Throws UnsupportedOperationException . |
void |
addLast |
Throws UnsupportedOperationException . |
E |
ceiling |
Returns the least element in this set greater than or equal to the given element, or null if there is no such element. |
void |
clear() |
Removes all of the elements from this set. |
Object |
clone() |
Returns a shallow copy of this TreeSet instance. |
Comparator |
comparator() |
Returns the comparator used to order the elements in this set, or null if this set uses the natural ordering of its elements. |
boolean |
contains |
Returns true if this set contains the specified element. |
Iterator |
descendingIterator() |
Returns an iterator over the elements in this set in descending order. |
NavigableSet |
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 |
Returns the greatest element in this set less than or equal to the given element, or null if there is no such element. |
SortedSet |
headSet |
Returns a view of the portion of this set whose elements are strictly less than toElement . |
NavigableSet |
headSet |
Returns a view of the portion of this set whose elements are less than (or equal to, if inclusive is true) toElement . |
E |
higher |
Returns the least element in this set strictly greater than the given element, or null if there is no such element. |
boolean |
isEmpty() |
Returns true if this set contains no elements. |
Iterator |
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 |
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. |
boolean |
remove |
Removes the specified element from this set if it is present. |
int |
size() |
Returns the number of elements in this set (its cardinality). |
Spliterator |
spliterator() |
Creates a late-binding and fail-fast Spliterator over the elements in this set. |
NavigableSet |
subSet |
Returns a view of the portion of this set whose elements range from fromElement to toElement . |
SortedSet |
subSet |
Returns a view of the portion of this set whose elements range from fromElement , inclusive, to toElement , exclusive. |
SortedSet |
tailSet |
Returns a view of the portion of this set whose elements are greater than or equal to fromElement . |
NavigableSet |
tailSet |
Returns a view of the portion of this set whose elements are greater than (or equal to, if inclusive is true) fromElement . |
equals, hashCode, removeAll
containsAll, retainAll, toArray, toArray, toString
parallelStream, removeIf, stream, toArray
removeFirst, removeLast, reversed
public TreeSet()
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
.public TreeSet(Comparator<? super E> 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
.comparator
- the comparator that will be used to order this set. If null
, the natural ordering of the elements will be used.public TreeSet(Collection<? extends E> c)
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.c
- collection whose elements will comprise the new setClassCastException
- if the elements in c
are not Comparable
, or are not mutually comparableNullPointerException
- if the specified collection is nullpublic TreeSet(SortedSet<E> s)
s
- sorted set whose elements will comprise the new setNullPointerException
- if the specified sorted set is nullpublic Iterator<E> iterator()
iterator
in interface Collection<E>
iterator
in interface Iterable<E>
iterator
in interface NavigableSet<E>
iterator
in interface Set<E>
iterator
in class AbstractCollection<E>
public Iterator<E> descendingIterator()
descendingIterator
in interface NavigableSet<E>
public NavigableSet<E> descendingSet()
NavigableSet
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
.
descendingSet
in interface NavigableSet<E>
public int size()
public boolean isEmpty()
true
if this set contains no elements.isEmpty
in interface Collection<E>
isEmpty
in interface Set<E>
isEmpty
in class AbstractCollection<E>
true
if this set contains no elementspublic boolean contains(Object o)
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)
.contains
in interface Collection<E>
contains
in interface Set<E>
contains
in class AbstractCollection<E>
o
- object to be checked for containment in this settrue
if this set contains the specified elementClassCastException
- if the specified object cannot be compared with the elements currently in the setNullPointerException
- if the specified element is null and this set uses natural ordering, or its comparator does not permit null elementspublic boolean add(E e)
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
.add
in interface Collection<E>
add
in interface Set<E>
add
in class AbstractCollection<E>
e
- element to be added to this settrue
if this set did not already contain the specified elementClassCastException
- if the specified object cannot be compared with the elements currently in this setNullPointerException
- if the specified element is null and this set uses natural ordering, or its comparator does not permit null elementspublic boolean remove(Object o)
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.)remove
in interface Collection<E>
remove
in interface Set<E>
remove
in class AbstractCollection<E>
o
- object to be removed from this set, if presenttrue
if this set contained the specified elementClassCastException
- if the specified object cannot be compared with the elements currently in this setNullPointerException
- if the specified element is null and this set uses natural ordering, or its comparator does not permit null elementspublic void clear()
clear
in interface Collection<E>
clear
in interface Set<E>
clear
in class AbstractCollection<E>
public boolean addAll(Collection<? extends E> c)
addAll
in interface Collection<E>
addAll
in interface Set<E>
addAll
in class AbstractCollection<E>
c
- collection containing elements to be added to this settrue
if this set changed as a result of the callClassCastException
- if the elements provided cannot be compared with the elements currently in the setNullPointerException
- 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 elementspublic NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive)
NavigableSet
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.
subSet
in interface NavigableSet<E>
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
, exclusiveClassCastException
- 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 uses natural ordering, or its comparator 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.public NavigableSet<E> headSet(E toElement, boolean inclusive)
NavigableSet
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.
headSet
in interface NavigableSet<E>
toElement
- high endpoint of the returned setinclusive
- true
if the high endpoint is to be included in the returned viewinclusive
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 uses natural ordering, or its comparator does not permit null elementsIllegalArgumentException
- if this set itself has a restricted range, and toElement
lies outside the bounds of the rangepublic NavigableSet<E> tailSet(E fromElement, boolean inclusive)
NavigableSet
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.
tailSet
in interface NavigableSet<E>
fromElement
- low endpoint of the returned setinclusive
- true
if the low endpoint is to be included in the returned viewfromElement
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 uses natural ordering, or its comparator does not permit null elementsIllegalArgumentException
- if this set itself has a restricted range, and fromElement
lies outside the bounds of the rangepublic SortedSet<E> subSet(E fromElement, E toElement)
NavigableSet
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)
.
subSet
in interface NavigableSet<E>
subSet
in interface SortedSet<E>
fromElement
- low endpoint (inclusive) of the returned settoElement
- high endpoint (exclusive) of the returned setfromElement
, inclusive, to toElement
, exclusiveClassCastException
- 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 uses natural ordering, or its comparator 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 rangepublic SortedSet<E> headSet(E toElement)
NavigableSet
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)
.
headSet
in interface NavigableSet<E>
headSet
in interface SortedSet<E>
toElement
- high endpoint (exclusive) of the returned settoElement
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 uses natural ordering, or its comparator does not permit null elementsIllegalArgumentException
- if this set itself has a restricted range, and toElement
lies outside the bounds of the rangepublic SortedSet<E> tailSet(E fromElement)
NavigableSet
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)
.
tailSet
in interface NavigableSet<E>
tailSet
in interface SortedSet<E>
fromElement
- low endpoint (inclusive) of the returned setfromElement
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 uses natural ordering, or its comparator does not permit null elementsIllegalArgumentException
- if this set itself has a restricted range, and fromElement
lies outside the bounds of the rangepublic Comparator<? super E> comparator()
SortedSet
null
if this set uses the natural ordering of its elements.comparator
in interface SortedSet<E>
null
if this set uses the natural ordering of its elementspublic E first()
SortedSet
first
in interface SortedSet<E>
NoSuchElementException
- if this set is emptypublic E last()
SortedSet
last
in interface SortedSet<E>
NoSuchElementException
- if this set is emptypublic E lower(E e)
NavigableSet
null
if there is no such element.lower
in interface NavigableSet<E>
e
- the value to matche
, or null
if there is no such elementClassCastException
- if the specified element cannot be compared with the elements currently in the setNullPointerException
- if the specified element is null and this set uses natural ordering, or its comparator does not permit null elementspublic E floor(E e)
NavigableSet
null
if there is no such element.floor
in interface NavigableSet<E>
e
- the value to matche
, or null
if there is no such elementClassCastException
- if the specified element cannot be compared with the elements currently in the setNullPointerException
- if the specified element is null and this set uses natural ordering, or its comparator does not permit null elementspublic E ceiling(E e)
NavigableSet
null
if there is no such element.ceiling
in interface NavigableSet<E>
e
- the value to matche
, or null
if there is no such elementClassCastException
- if the specified element cannot be compared with the elements currently in the setNullPointerException
- if the specified element is null and this set uses natural ordering, or its comparator does not permit null elementspublic E higher(E e)
NavigableSet
null
if there is no such element.higher
in interface NavigableSet<E>
e
- the value to matche
, or null
if there is no such elementClassCastException
- if the specified element cannot be compared with the elements currently in the setNullPointerException
- if the specified element is null and this set uses natural ordering, or its comparator does not permit null elementspublic E pollFirst()
NavigableSet
null
if this set is empty.pollFirst
in interface NavigableSet<E>
null
if this set is emptypublic E pollLast()
NavigableSet
null
if this set is empty.pollLast
in interface NavigableSet<E>
null
if this set is emptypublic void addFirst(E e)
UnsupportedOperationException
. The encounter order induced by this set's comparison method determines the position of elements, so explicit positioning is not supported.addFirst
in interface SequencedCollection<E>
addFirst
in interface SortedSet<E>
e
- the element to be addedUnsupportedOperationException
- alwayspublic void addLast(E e)
UnsupportedOperationException
. The encounter order induced by this set's comparison method determines the position of elements, so explicit positioning is not supported.addLast
in interface SequencedCollection<E>
addLast
in interface SortedSet<E>
e
- the element to be added.UnsupportedOperationException
- alwayspublic Object clone()
TreeSet
instance. (The elements themselves are not cloned.)public Spliterator<E> spliterator()
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.
spliterator
in interface Collection<E>
spliterator
in interface Iterable<E>
spliterator
in interface Set<E>
spliterator
in interface SortedSet<E>
Spliterator
over the elements in this set
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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.
https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/TreeSet.html