java.util

Class TreeSet<T>

public class TreeSet<T> extends AbstractSet<T> implements SortedSet<T>, Cloneable, Serializable

This class provides a TreeMap-backed implementation of the SortedSet interface. The elements will be sorted according to their natural order, or according to the provided Comparator.

Most operations are O(log n), but there is so much overhead that this makes small sets expensive. Note that the ordering must be consistent with equals to correctly implement the Set interface. If this condition is violated, the set is still well-behaved, but you may have suprising results when comparing it to other sets.

This implementation is not synchronized. If you need to share this between multiple threads, do something like:
SortedSet s = Collections.synchronizedSortedSet(new TreeSet(...));

The iterators are fail-fast, meaning that any structural modification, except for remove() called on the iterator itself, cause the iterator to throw a ConcurrentModificationException rather than exhibit non-deterministic behavior.

Since: 1.2

See Also: Collection Set HashSet LinkedHashSet Comparable Comparator synchronizedSortedSet TreeMap

UNKNOWN: updated to 1.4

Constructor Summary
TreeSet()
Construct a new TreeSet whose backing TreeMap using the "natural" ordering of keys.
TreeSet(Comparator<? super T> comparator)
Construct a new TreeSet whose backing TreeMap uses the supplied Comparator.
TreeSet(Collection<? extends T> collection)
Construct a new TreeSet whose backing TreeMap uses the "natural" orering of the keys and which contains all of the elements in the supplied Collection.
TreeSet(SortedSet<T> sortedSet)
Construct a new TreeSet, using the same key ordering as the supplied SortedSet and containing all of the elements in the supplied SortedSet.
Method Summary
booleanadd(T obj)
Adds the spplied Object to the Set if it is not already in the Set; returns true if the element is added, false otherwise.
booleanaddAll(Collection<? extends T> c)
Adds all of the elements in the supplied Collection to this TreeSet.
voidclear()
Removes all elements in this Set.
Objectclone()
Returns a shallow copy of this Set.
Comparator<? super T>comparator()
Returns this Set's comparator.
booleancontains(Object obj)
Returns true if this Set contains the supplied Object, false otherwise.
Tfirst()
Returns the first (by order) element in this Set.
SortedSet<T>headSet(T to)
Returns a view of this Set including all elements less than to.
booleanisEmpty()
Returns true if this Set has size 0, false otherwise.
Iterator<T>iterator()
Returns in Iterator over the elements in this TreeSet, which traverses in ascending order.
Tlast()
Returns the last (by order) element in this Set.
booleanremove(Object obj)
If the supplied Object is in this Set, it is removed, and true is returned; otherwise, false is returned.
intsize()
Returns the number of elements in this Set
SortedSet<T>subSet(T from, T to)
Returns a view of this Set including all elements greater or equal to from and less than to (a half-open interval).
SortedSet<T>tailSet(T from)
Returns a view of this Set including all elements greater or equal to from.

Constructor Detail

TreeSet

public TreeSet()
Construct a new TreeSet whose backing TreeMap using the "natural" ordering of keys. Elements that are not mutually comparable will cause ClassCastExceptions down the road.

See Also: Comparable

TreeSet

public TreeSet(Comparator<? super T> comparator)
Construct a new TreeSet whose backing TreeMap uses the supplied Comparator. Elements that are not mutually comparable will cause ClassCastExceptions down the road.

Parameters: comparator the Comparator this Set will use

TreeSet

public TreeSet(Collection<? extends T> collection)
Construct a new TreeSet whose backing TreeMap uses the "natural" orering of the keys and which contains all of the elements in the supplied Collection. This runs in n*log(n) time.

Parameters: collection the new Set will be initialized with all of the elements in this Collection

Throws: ClassCastException if the elements of the collection are not comparable NullPointerException if the collection is null

See Also: Comparable

TreeSet

public TreeSet(SortedSet<T> sortedSet)
Construct a new TreeSet, using the same key ordering as the supplied SortedSet and containing all of the elements in the supplied SortedSet. This constructor runs in linear time.

Parameters: sortedSet the new TreeSet will use this SortedSet's comparator and will initialize itself with all its elements

Throws: NullPointerException if sortedSet is null

Method Detail

add

public boolean add(T obj)
Adds the spplied Object to the Set if it is not already in the Set; returns true if the element is added, false otherwise.

Parameters: obj the Object to be added to this Set

Throws: ClassCastException if the element cannot be compared with objects already in the set

addAll

public boolean addAll(Collection<? extends T> c)
Adds all of the elements in the supplied Collection to this TreeSet.

Parameters: c The collection to add

Returns: true if the Set is altered, false otherwise

Throws: NullPointerException if c is null ClassCastException if an element in c cannot be compared with objects already in the set

clear

public void clear()
Removes all elements in this Set.

clone

public Object clone()
Returns a shallow copy of this Set. The elements are not cloned.

Returns: the cloned set

comparator

public Comparator<? super T> comparator()
Returns this Set's comparator.

Returns: the comparator, or null if the set uses natural ordering

contains

public boolean contains(Object obj)
Returns true if this Set contains the supplied Object, false otherwise.

Parameters: obj the Object to check for

Returns: true if it is in the set

Throws: ClassCastException if obj cannot be compared with objects already in the set

first

public T first()
Returns the first (by order) element in this Set.

Returns: the first element

Throws: NoSuchElementException if the set is empty

headSet

public SortedSet<T> headSet(T to)
Returns a view of this Set including all elements less than to. The returned set is backed by the original, so changes in one appear in the other. The subset will throw an {@link IllegalArgumentException} for any attempt to access or add an element beyond the specified cutoff. The returned set does not include the endpoint; if you want inclusion, pass the successor element.

Parameters: to the (exclusive) cutoff point

Returns: a view of the set less than the cutoff

Throws: ClassCastException if to is not compatible with the comparator (or is not Comparable, for natural ordering) NullPointerException if to is null, but the comparator does not tolerate null elements

isEmpty

public boolean isEmpty()
Returns true if this Set has size 0, false otherwise.

Returns: true if the set is empty

iterator

public Iterator<T> iterator()
Returns in Iterator over the elements in this TreeSet, which traverses in ascending order.

Returns: an iterator

last

public T last()
Returns the last (by order) element in this Set.

Returns: the last element

Throws: NoSuchElementException if the set is empty

remove

public boolean remove(Object obj)
If the supplied Object is in this Set, it is removed, and true is returned; otherwise, false is returned.

Parameters: obj the Object to remove from this Set

Returns: true if the set was modified

Throws: ClassCastException if obj cannot be compared to set elements

size

public int size()
Returns the number of elements in this Set

Returns: the set size

subSet

public SortedSet<T> subSet(T from, T to)
Returns a view of this Set including all elements greater or equal to from and less than to (a half-open interval). The returned set is backed by the original, so changes in one appear in the other. The subset will throw an {@link IllegalArgumentException} for any attempt to access or add an element beyond the specified cutoffs. The returned set includes the low endpoint but not the high; if you want to reverse this behavior on either end, pass in the successor element.

Parameters: from the (inclusive) low cutoff point to the (exclusive) high cutoff point

Returns: a view of the set between the cutoffs

Throws: ClassCastException if either cutoff is not compatible with the comparator (or is not Comparable, for natural ordering) NullPointerException if from or to is null, but the comparator does not tolerate null elements IllegalArgumentException if from is greater than to

tailSet

public SortedSet<T> tailSet(T from)
Returns a view of this Set including all elements greater or equal to from. The returned set is backed by the original, so changes in one appear in the other. The subset will throw an {@link IllegalArgumentException} for any attempt to access or add an element beyond the specified cutoff. The returned set includes the endpoint; if you want to exclude it, pass in the successor element.

Parameters: from the (inclusive) low cutoff point

Returns: a view of the set above the cutoff

Throws: ClassCastException if from is not compatible with the comparator (or is not Comparable, for natural ordering) NullPointerException if from is null, but the comparator does not tolerate null elements