E
- the type of elements maintained by this setpublic class TreeSet<E> extends java.util.AbstractSet<E> implements NavigableSet<E>, java.lang.Cloneable, java.io.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.
This class is a member of the Java Collections Framework.
Collection
,
Set
,
HashSet
,
Comparable
,
Comparator
,
TreeMap
,
Serialized FormConstructor and Description |
---|
TreeSet()
Constructs a new, empty tree set, sorted according to the natural ordering of its elements.
|
TreeSet(java.util.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(java.util.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.
|
Modifier and Type | Method and Description |
---|---|
boolean |
add(E e)
Adds the specified element to this set if it is not already present.
|
boolean |
addAll(java.util.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
null if there is no such element. |
void |
clear()
Removes all of the elements from this set.
|
java.lang.Object |
clone()
Returns a shallow copy of this
TreeSet instance. |
java.util.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.
|
boolean |
contains(java.lang.Object o)
Returns
true if this set contains the specified 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 |
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
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. |
boolean |
isEmpty()
Returns
true if this set contains no elements. |
java.util.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
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(java.lang.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).
|
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 . |
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(java.util.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(java.util.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 setjava.lang.ClassCastException
- if the elements in c
are not Comparable
, or are not mutually comparablejava.lang.NullPointerException
- if the specified collection is nullpublic java.util.Iterator<E> iterator()
iterator
in interface java.lang.Iterable<E>
iterator
in interface java.util.Collection<E>
iterator
in interface NavigableSet<E>
iterator
in interface java.util.Set<E>
iterator
in class java.util.AbstractCollection<E>
public java.util.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.public boolean contains(java.lang.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
(o==null ? e==null : o.equals(e)).contains
in interface java.util.Collection<E>
contains
in interface java.util.Set<E>
contains
in class java.util.AbstractCollection<E>
o
- object to be checked for containment in this settrue
if this set contains the specified elementjava.lang.ClassCastException
- if the specified object cannot be compared with the elements currently in the setjava.lang.NullPointerException
- 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
(e==null ? e2==null : e.equals(e2)). If this set already contains the element, the
call leaves the set unchanged and returns false
.add
in interface java.util.Collection<E>
add
in interface java.util.Set<E>
add
in class java.util.AbstractCollection<E>
e
- element to be added to this settrue
if this set did not already contain the specified elementjava.lang.ClassCastException
- if the specified object cannot be compared with the elements currently in this setjava.lang.NullPointerException
- if the specified element is null and this set uses natural ordering, or its comparator does not
permit null elementspublic boolean remove(java.lang.Object o)
e
such
that (o==null ? e==null : o.equals(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 java.util.Collection<E>
remove
in interface java.util.Set<E>
remove
in class java.util.AbstractCollection<E>
o
- object to be removed from this set, if presenttrue
if this set contained the specified elementjava.lang.ClassCastException
- if the specified object cannot be compared with the elements currently in this setjava.lang.NullPointerException
- if the specified element is null and this set uses natural ordering, or its comparator does not
permit null elementspublic void clear()
public boolean addAll(java.util.Collection<? extends E> c)
addAll
in interface java.util.Collection<E>
addAll
in interface java.util.Set<E>
addAll
in class java.util.AbstractCollection<E>
c
- collection containing elements to be added to this settrue
if this set changed as a result of the calljava.lang.ClassCastException
- if the elements provided cannot be compared with the elements currently in the setjava.lang.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 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
, 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 uses natural ordering, or its
comparator 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.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
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 uses natural ordering, or its comparator does not permit
null elementsjava.lang.IllegalArgumentException
- 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
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 uses natural ordering, or its comparator does not permit
null elementsjava.lang.IllegalArgumentException
- 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
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 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 uses natural ordering, or its
comparator 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 rangepublic SortedSet<E> headSet(E toElement)
NavigableSet
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 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 uses natural ordering, or its comparator does not permit
null elementsjava.lang.IllegalArgumentException
- if this set itself has a
restricted range, and toElement lies outside the
bounds of the rangepublic SortedSet<E> tailSet(E fromElement)
NavigableSet
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 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 uses natural ordering, or its comparator does not permit
null elementsjava.lang.IllegalArgumentException
- if this set itself has a
restricted range, and fromElement lies outside the
bounds of the rangepublic java.util.Comparator<? super E> comparator()
SortedSet
comparator
in interface SortedSet<E>
public E first()
SortedSet
public E last()
SortedSet
public 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 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 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 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 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 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 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 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 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 java.lang.Object clone()
TreeSet
instance. (The elements themselves are not cloned.)clone
in class java.lang.Object