E - the type of elements maintained by this setpublic 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.
This class is a member of the Java Collections Framework.
Collection,
Set,
HashSet,
Comparable,
Comparator,
TreeMap,
Serialized Form| Constructor and 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.
|
| 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(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.
|
Object |
clone()
Returns a shallow copy of this
TreeSet instance. |
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(Object o)
Returns
true if this set contains the specified element. |
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. |
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(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. |
equals, hashCode, removeAllcontainsAll, retainAll, toArray, toArray, toStringpublic 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(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(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(SortedSet<E> s)
s - sorted set whose elements will comprise the new setNullPointerException - if the specified sorted set is nullpublic 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 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 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 elementsAbstractCollection.add(Object)public E ceiling(E e)
NavigableSetnull 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 void clear()
clear in interface Collection<E>clear in interface Set<E>clear in class AbstractCollection<E>public Object clone()
TreeSet instance. (The elements themselves are not cloned.)public Comparator<? super E> comparator()
SortedSetcomparator in interface SortedSet<E>public 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
(o==null ? e==null : o.equals(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 Iterator<E> descendingIterator()
descendingIterator in interface NavigableSet<E>public NavigableSet<E> descendingSet()
NavigableSetremove 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 E first()
SortedSetfirst in interface SortedSet<E>NoSuchElementException - if this set is emptypublic E floor(E e)
NavigableSetnull 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 SortedSet<E> headSet(E toElement)
NavigableSetThe 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 setClassCastException - 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> headSet(E toElement, boolean inclusive)
NavigableSetinclusive 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) toElementClassCastException - 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 E higher(E e)
NavigableSetnull 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 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 Iterator<E> iterator()
iterator in interface Iterable<E>iterator in interface Collection<E>iterator in interface NavigableSet<E>iterator in interface Set<E>iterator in class AbstractCollection<E>public E last()
SortedSetlast in interface SortedSet<E>NoSuchElementException - if this set is emptypublic E lower(E e)
NavigableSetnull 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 pollFirst()
NavigableSetnull if this set is empty.pollFirst in interface NavigableSet<E>null if this set is emptypublic E pollLast()
NavigableSetnull if this set is empty.pollLast in interface NavigableSet<E>null if this set is emptypublic boolean remove(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 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 int size()
size in interface Collection<E>size in interface Set<E>size in class AbstractCollection<E>public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive)
NavigableSetfromElement 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 SortedSet<E> subSet(E fromElement, E toElement)
NavigableSetThe 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 setClassCastException - 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> tailSet(E fromElement)
NavigableSetThe 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 setClassCastException - 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 NavigableSet<E> tailSet(E fromElement, boolean inclusive)
NavigableSetinclusive 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 viewfromElementClassCastException - 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 range