java.util
class TreeSet

java.lang.Object java.util.AbstractCollection java.util.AbstractSet java.util.TreeSet

All Implemented Interfaces:

Serializable, Cloneable, Collection, NavigableSet, Set

Most common way to construct:

TreeSet ts = new TreeSet();

Based on 114 examples

public class TreeSet
extends AbstractSet
implements NavigableSet, Cloneable, Serializable

A {@link NavigableSet} implementation based on a {@link TreeMap}. The elements are ordered using their {@linkplain Comparable natural ordering}, or by a {@link Comparator} provided at set creation time, depending on which constructor is used.

This implementation provides guaranteed log(n) time cost for the basic operations ({@code add}, {@code remove} and {@code 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 {@code Set} interface. (See {@code Comparable} or {@code Comparator} for a precise definition of consistent with equals.) This is so because the {@code Set} interface is defined in terms of the {@code equals} operation, but a {@code TreeSet} instance performs all element comparisons using its {@code compareTo} (or {@code 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 {@code 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 {@link Collections#synchronizedSortedSet 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 {@code 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 {@code remove} method, the iterator will throw a {@link 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 {@code 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.

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 {@link Comparable} interface. Furthermore, all such elements must be mutually comparable: {@code e1.compareTo(e2)} must not throw a {@code ClassCastException} for any elements {@code e1} and {@code 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 {@code add} call will throw a {@code ClassCastException}.

TreeSet

public TreeSet(Collection 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 {@link Comparable} interface. Furthermore, all such elements must be mutually comparable: {@code e1.compareTo(e2)} must not throw a {@code ClassCastException} for any elements {@code e1} and {@code e2} in the set.

Parameters:

c - collection whose elements will comprise the new set

TreeSet

public TreeSet(Comparator 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: {@code comparator.compare(e1, e2)} must not throw a {@code ClassCastException} for any elements {@code e1} and {@code e2} in the set. If the user attempts to add an element to the set that violates this constraint, the {@code add} call will throw a {@code ClassCastException}.

Parameters:

comparator - the comparator that will be used to order this set. If {@code null}, the {@linkplain Comparable natural ordering} of the elements will be used.

TreeSet

public TreeSet(SortedSet 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

add

public boolean add(Object e)

Adds the specified element to this set if it is not already present. More formally, adds the specified element {@code e} to this set if the set contains no element {@code 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 {@code false}.

Overrides:

add in class AbstractCollection

Parameters:

e - element to be added to this set

Returns:

{@code true} if this set did not already contain the specified element

addAll

public boolean addAll(Collection c)

Adds all of the elements in the specified collection to this set.

Overrides:

addAll in class AbstractCollection

Parameters:

c - collection containing elements to be added to this set

Returns:

{@code true} if this set changed as a result of the call

ceiling

public Object ceiling(Object e)

Parameters:

e

clear

public void clear()

Removes all of the elements from this set. The set will be empty after this call returns.

Overrides:

clear in class AbstractCollection

clone

public Object clone()

Returns a shallow copy of this {@code TreeSet} instance. (The elements themselves are not cloned.)

Overrides:

clone in class Object

Returns:

a shallow copy of this set

comparator

public Comparator comparator()

contains

public boolean contains(Object o)

Returns {@code true} if this set contains the specified element. More formally, returns {@code true} if and only if this set contains an element {@code e} such that (o==null ? e==null : o.equals(e)).

Overrides:

contains in class AbstractCollection

Parameters:

o - object to be checked for containment in this set

Returns:

{@code true} if this set contains the specified element

descendingIterator

public Iterator descendingIterator()

Returns an iterator over the elements in this set in descending order.

Returns:

an iterator over the elements in this set in descending order

descendingSet

public NavigableSet descendingSet()

first

public Object first()

floor

public Object floor(Object e)

Parameters:

e

headSet

public SortedSet headSet(Object toElement)

Parameters:

toElement

headSet

public NavigableSet headSet(Object toElement,
                            boolean inclusive)

Parameters:

toElement

inclusive

higher

public Object higher(Object e)

Parameters:

e

isEmpty

public boolean isEmpty()

Returns {@code true} if this set contains no elements.

Overrides:

isEmpty in class AbstractCollection

Returns:

{@code true} if this set contains no elements

iterator

public Iterator iterator()

Returns an iterator over the elements in this set in ascending order.

Overrides:

iterator in class AbstractCollection

Returns:

an iterator over the elements in this set in ascending order

last

public Object last()

lower

public Object lower(Object e)

Parameters:

e

pollFirst

public Object pollFirst()

pollLast

public Object pollLast()

remove

public boolean remove(Object o)

Removes the specified element from this set if it is present. More formally, removes an element {@code e} such that (o==null ? e==null : o.equals(e)), if this set contains such an element. Returns {@code 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.)

Overrides:

remove in class AbstractCollection

Parameters:

o - object to be removed from this set, if present

Returns:

{@code true} if this set contained the specified element

size

public int size()

Returns the number of elements in this set (its cardinality).

Overrides:

size in class AbstractCollection

Returns:

the number of elements in this set (its cardinality)

subSet

public NavigableSet subSet(Object fromElement,
                           boolean fromInclusive,
                           Object toElement,
                           boolean toInclusive)

Parameters:

fromElement

fromInclusive

toElement

toInclusive

subSet

public SortedSet subSet(Object fromElement,
                        Object toElement)

Parameters:

fromElement

toElement

tailSet

public SortedSet tailSet(Object fromElement)

Parameters:

fromElement

tailSet

public NavigableSet tailSet(Object fromElement,
                            boolean inclusive)

Parameters:

fromElement

inclusive