Class TreeSet<E>
 java.lang.Object

 java.util.AbstractCollection<E>

 java.util.AbstractSet<E>

 java.util.TreeSet<E>
 Type Parameters:

E
 the type of elements maintained by this set
 All Implemented Interfaces:

Serializable
,Cloneable
,Iterable<E>
,Collection<E>
,NavigableSet<E>
,Set<E>
,SortedSet<E>
public class TreeSet<E> extends AbstractSet<E> implements NavigableSet<E>, Cloneable, Serializable
A 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 welldefined 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 failfast: 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, nondeterministic behavior at an undetermined time in the future.
Note that the failfast 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. Failfast iterators throw ConcurrentModificationException
on a besteffort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the failfast behavior of iterators should be used only to detect bugs.
This class is a member of the Java Collections Framework.
 Since:
 1.2
 See Also:

Collection
,Set
,HashSet
,Comparable
,Comparator
,TreeMap
, Serialized Form
Constructor Summary
Constructor  Description 

TreeSet()  Constructs a new, empty tree set, sorted according to the natural ordering of its elements. 
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(Comparator<? super E> comparator)  Constructs a new, empty tree set, sorted according to the specified comparator. 
TreeSet(SortedSet<E> s)  Constructs a new tree set containing the same elements and using the same ordering as the specified sorted set. 
Method Summary
Modifier and Type  Method  Description 

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. 
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 
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 
SortedSet<E>  headSet(E toElement)  Returns a view of the portion of this set whose elements are strictly less than 
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 
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 latebinding and failfast 
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 
SortedSet<E>  tailSet(E fromElement)  Returns a view of the portion of this set whose elements are greater than or equal 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 
Methods declared in class java.util.AbstractSet
equals, hashCode, removeAll
Methods declared in class java.util.AbstractCollection
containsAll, retainAll, toArray, toArray, toString
Methods declared in class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait
Methods declared in interface java.util.Collection
parallelStream, removeIf, stream, toArray
Methods declared in interface java.lang.Iterable
forEach
Methods declared in interface java.util.Set
containsAll, equals, hashCode, removeAll, retainAll, toArray, toArray
Methods declared in interface java.util.SortedSet
comparator
Constructor Detail
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
 the comparator that will be used to order this set. Ifnull
, the natural 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 whose elements will comprise the new set  Throws:

ClassCastException
 if the elements inc
are notComparable
, 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
 sorted set whose elements will comprise the new set  Throws:

NullPointerException
 if the specified sorted set is null
Method Detail
iterator
public Iterator<E> iterator()
Returns an iterator over the elements in this set in ascending order.
 Specified by:

iterator
in interfaceCollection<E>
 Specified by:

iterator
in interfaceIterable<E>
 Specified by:

iterator
in interfaceNavigableSet<E>
 Specified by:

iterator
in interfaceSet<E>
 Specified by:

iterator
in classAbstractCollection<E>
 Returns:
 an iterator over the elements in this set in ascending order
descendingIterator
public Iterator<E> descendingIterator()
Returns an iterator over the elements in this set in descending order.
 Specified by:

descendingIterator
in interfaceNavigableSet<E>
 Returns:
 an iterator over the elements in this set in descending order
 Since:
 1.6
descendingSet
public NavigableSet<E> descendingSet()
Description copied from interface: NavigableSet
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 viceversa. 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
.
 Specified by:

descendingSet
in interfaceNavigableSet<E>
 Returns:
 a reverse order view of this set
 Since:
 1.6
size
public int size()
Returns the number of elements in this set (its cardinality).
 Specified by:

size
in interfaceCollection<E>
 Specified by:

size
in interfaceSet<E>
 Returns:
 the number of elements in this set (its cardinality)
isEmpty
public boolean isEmpty()
Returns true
if this set contains no elements.
 Specified by:

isEmpty
in interfaceCollection<E>
 Specified by:

isEmpty
in interfaceSet<E>
 Overrides:

isEmpty
in classAbstractCollection<E>
 Returns:

true
if this set contains no 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)
.
 Specified by:

contains
in interfaceCollection<E>
 Specified by:

contains
in interfaceSet<E>
 Overrides:

contains
in classAbstractCollection<E>
 Parameters:

o
 object to be checked for containment in this set  Returns:

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
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
.
 Specified by:

add
in interfaceCollection<E>
 Specified by:

add
in interfaceSet<E>
 Overrides:

add
in classAbstractCollection<E>
 Parameters:

e
 element to be added to this set  Returns:

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
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.)
 Specified by:

remove
in interfaceCollection<E>
 Specified by:

remove
in interfaceSet<E>
 Overrides:

remove
in classAbstractCollection<E>
 Parameters:

o
 object to be removed from this set, if present  Returns:

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
clear
public void clear()
Removes all of the elements from this set. The set will be empty after this call returns.
 Specified by:

clear
in interfaceCollection<E>
 Specified by:

clear
in interfaceSet<E>
 Overrides:

clear
in classAbstractCollection<E>
addAll
public boolean addAll(Collection<? extends E> c)
Adds all of the elements in the specified collection to this set.
 Specified by:

addAll
in interfaceCollection<E>
 Specified by:

addAll
in interfaceSet<E>
 Overrides:

addAll
in classAbstractCollection<E>
 Parameters:

c
 collection containing elements to be added to this set  Returns:

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  See Also:
AbstractCollection.add(Object)
subSet
public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive)
Description copied from interface: NavigableSet
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 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.
 Specified by:

subSet
in interfaceNavigableSet<E>
 Parameters:

fromElement
 low endpoint of the returned set 
fromInclusive
true
if the low endpoint is to be included in the returned view 
toElement
 high endpoint of the returned set 
toInclusive
true
if the high endpoint is to be included in the returned view  Returns:
 a view of the portion of this set whose elements range from
fromElement
, inclusive, totoElement
, exclusive  Throws:

ClassCastException
 iffromElement
andtoElement
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 iffromElement
ortoElement
cannot be compared to elements currently in the set. 
NullPointerException
 iffromElement
ortoElement
is null and this set uses natural ordering, or its comparator does not permit null elements 
IllegalArgumentException
 iffromElement
is greater thantoElement
; or if this set itself has a restricted range, andfromElement
ortoElement
lies outside the bounds of the range.  Since:
 1.6
headSet
public NavigableSet<E> headSet(E toElement, boolean inclusive)
Description copied from interface: NavigableSet
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 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.
 Specified by:

headSet
in interfaceNavigableSet<E>
 Parameters:

toElement
 high endpoint of the returned set 
inclusive
true
if the high endpoint is to be included in the returned view  Returns:
 a view of the portion of this set whose elements are less than (or equal to, if
inclusive
is true)toElement
 Throws:

ClassCastException
 iftoElement
is not compatible with this set's comparator (or, if the set has no comparator, iftoElement
does not implementComparable
). Implementations may, but are not required to, throw this exception iftoElement
cannot be compared to elements currently in the set. 
NullPointerException
 iftoElement
is null and this set uses natural ordering, or its comparator does not permit null elements 
IllegalArgumentException
 if this set itself has a restricted range, andtoElement
lies outside the bounds of the range  Since:
 1.6
tailSet
public NavigableSet<E> tailSet(E fromElement, boolean inclusive)
Description copied from interface: NavigableSet
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 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.
 Specified by:

tailSet
in interfaceNavigableSet<E>
 Parameters:

fromElement
 low endpoint of the returned set 
inclusive
true
if the low endpoint is to be included in the returned view  Returns:
 a view of the portion of this set whose elements are greater than or equal to
fromElement
 Throws:

ClassCastException
 iffromElement
is not compatible with this set's comparator (or, if the set has no comparator, iffromElement
does not implementComparable
). Implementations may, but are not required to, throw this exception iffromElement
cannot be compared to elements currently in the set. 
NullPointerException
 iffromElement
is null and this set uses natural ordering, or its comparator does not permit null elements 
IllegalArgumentException
 if this set itself has a restricted range, andfromElement
lies outside the bounds of the range  Since:
 1.6
subSet
public SortedSet<E> subSet(E fromElement, E toElement)
Description copied from interface: NavigableSet
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 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.
Equivalent to subSet(fromElement, true, toElement, false)
.
 Specified by:

subSet
in interfaceNavigableSet<E>
 Specified by:

subSet
in interfaceSortedSet<E>
 Parameters:

fromElement
 low endpoint (inclusive) of the returned set 
toElement
 high endpoint (exclusive) of the returned set  Returns:
 a view of the portion of this set whose elements range from
fromElement
, inclusive, totoElement
, exclusive  Throws:

ClassCastException
 iffromElement
andtoElement
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 iffromElement
ortoElement
cannot be compared to elements currently in the set. 
NullPointerException
 iffromElement
ortoElement
is null and this set uses natural ordering, or its comparator does not permit null elements 
IllegalArgumentException
 iffromElement
is greater thantoElement
; or if this set itself has a restricted range, andfromElement
ortoElement
lies outside the bounds of the range
headSet
public SortedSet<E> headSet(E toElement)
Description copied from interface: NavigableSet
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 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.
Equivalent to headSet(toElement, false)
.
 Specified by:

headSet
in interfaceNavigableSet<E>
 Specified by:

headSet
in interfaceSortedSet<E>
 Parameters:

toElement
 high endpoint (exclusive) of the returned set  Returns:
 a view of the portion of this set whose elements are strictly less than
toElement
 Throws:

ClassCastException
 iftoElement
is not compatible with this set's comparator (or, if the set has no comparator, iftoElement
does not implementComparable
). Implementations may, but are not required to, throw this exception iftoElement
cannot be compared to elements currently in the set. 
NullPointerException
 iftoElement
is null and this set uses natural ordering, or its comparator does not permit null elements 
IllegalArgumentException
 if this set itself has a restricted range, andtoElement
lies outside the bounds of the range
tailSet
public SortedSet<E> tailSet(E fromElement)
Description copied from interface: NavigableSet
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 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.
Equivalent to tailSet(fromElement, true)
.
 Specified by:

tailSet
in interfaceNavigableSet<E>
 Specified by:

tailSet
in interfaceSortedSet<E>
 Parameters:

fromElement
 low endpoint (inclusive) of the returned set  Returns:
 a view of the portion of this set whose elements are greater than or equal to
fromElement
 Throws:

ClassCastException
 iffromElement
is not compatible with this set's comparator (or, if the set has no comparator, iffromElement
does not implementComparable
). Implementations may, but are not required to, throw this exception iffromElement
cannot be compared to elements currently in the set. 
NullPointerException
 iffromElement
is null and this set uses natural ordering, or its comparator does not permit null elements 
IllegalArgumentException
 if this set itself has a restricted range, andfromElement
lies outside the bounds of the range
first
public E first()
Description copied from interface: SortedSet
Returns the first (lowest) element currently in this set.
 Specified by:

first
in interfaceSortedSet<E>
 Returns:
 the first (lowest) element currently in this set
 Throws:

NoSuchElementException
 if this set is empty
last
public E last()
Description copied from interface: SortedSet
Returns the last (highest) element currently in this set.
 Specified by:

last
in interfaceSortedSet<E>
 Returns:
 the last (highest) element currently in this set
 Throws:

NoSuchElementException
 if this set is empty
lower
public E lower(E e)
Description copied from interface: NavigableSet
Returns the greatest element in this set strictly less than the given element, or null
if there is no such element.
 Specified by:

lower
in interfaceNavigableSet<E>
 Parameters:

e
 the value to match  Returns:
 the greatest element less than
e
, ornull
if there is no such element  Throws:

ClassCastException
 if the specified element 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  Since:
 1.6
floor
public E floor(E e)
Description copied from interface: NavigableSet
Returns the greatest element in this set less than or equal to the given element, or null
if there is no such element.
 Specified by:

floor
in interfaceNavigableSet<E>
 Parameters:

e
 the value to match  Returns:
 the greatest element less than or equal to
e
, ornull
if there is no such element  Throws:

ClassCastException
 if the specified element 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  Since:
 1.6
ceiling
public E ceiling(E e)
Description copied from interface: NavigableSet
Returns the least element in this set greater than or equal to the given element, or null
if there is no such element.
 Specified by:

ceiling
in interfaceNavigableSet<E>
 Parameters:

e
 the value to match  Returns:
 the least element greater than or equal to
e
, ornull
if there is no such element  Throws:

ClassCastException
 if the specified element 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  Since:
 1.6
higher
public E higher(E e)
Description copied from interface: NavigableSet
Returns the least element in this set strictly greater than the given element, or null
if there is no such element.
 Specified by:

higher
in interfaceNavigableSet<E>
 Parameters:

e
 the value to match  Returns:
 the least element greater than
e
, ornull
if there is no such element  Throws:

ClassCastException
 if the specified element 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  Since:
 1.6
pollFirst
public E pollFirst()
Description copied from interface: NavigableSet
Retrieves and removes the first (lowest) element, or returns null
if this set is empty.
 Specified by:

pollFirst
in interfaceNavigableSet<E>
 Returns:
 the first element, or
null
if this set is empty  Since:
 1.6
pollLast
public E pollLast()
Description copied from interface: NavigableSet
Retrieves and removes the last (highest) element, or returns null
if this set is empty.
 Specified by:

pollLast
in interfaceNavigableSet<E>
 Returns:
 the last element, or
null
if this set is empty  Since:
 1.6
clone
public Object clone()
Returns a shallow copy of this TreeSet
instance. (The elements themselves are not cloned.)
spliterator
public Spliterator<E> spliterator()
Creates a latebinding and failfast 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 SortedSet.comparator()
) is null
. Otherwise, the spliterator's comparator is the same as or imposes the same total ordering as the tree set's comparator.
 Specified by:

spliterator
in interfaceCollection<E>
 Specified by:

spliterator
in interfaceIterable<E>
 Specified by:

spliterator
in interfaceSet<E>
 Specified by:

spliterator
in interfaceSortedSet<E>
 Returns:
 a
Spliterator
over the elements in this set  Since:
 1.8