java.util

Class TreeSet<T>

Implemented Interfaces:
Cloneable, Collection<E>, Iterable<E>, NavigableSet<E>, Serializable, Set<E>, SortedSet<E>

public class TreeSet<T>
extends AbstractSet<E>
implements NavigableSet<E>, 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, Collections.synchronizedSortedSet(SortedSet), TreeMap, Serialized Form

Constructor Summary

TreeSet()
Construct a new TreeSet whose backing TreeMap using the "natural" ordering of keys.
TreeSet(SortedSet sortedSet)
Construct a new TreeSet, using the same key ordering as the supplied SortedSet and containing all of the elements in the supplied SortedSet.
TreeSet(T> comparator)
Construct a new TreeSet whose backing TreeMap uses the supplied Comparator.
TreeSet(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.

Method Summary

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.
boolean
addAll(T> c)
Adds all of the elements in the supplied Collection to this TreeSet.
T
ceiling(T e)
Returns the least or lowest element in the set greater than or equal to the given element, or null if there is no such element.
void
clear()
Removes all elements in this Set.
Object
clone()
Returns a shallow copy of this Set.
boolean
contains(Object obj)
Returns true if this Set contains the supplied Object, false otherwise.
Iterator
descendingIterator()
Returns an iterator over the elements of this set in descending order.
NavigableSet
descendingSet()
Returns a view of the set in reverse order.
T
first()
Returns the first (by order) element in this Set.
T
floor(T e)
Returns the greatest or highest element in the set less than or equal to the given element, or null if there is no such element.
SortedSet
headSet(T to)
Returns a view of this Set including all elements less than to.
NavigableSet
headSet(T to, boolean inclusive)
Returns a view of this Set including all elements less than (or equal to, if inclusive is true) to.
T
higher(T e)
Returns the least or lowest element in the set strictly greater than the given element, or null if there is no such element.
boolean
isEmpty()
Returns true if this Set has size 0, false otherwise.
Iterator
iterator()
Returns in Iterator over the elements in this TreeSet, which traverses in ascending order.
T
last()
Returns the last (by order) element in this Set.
T
lower(T e)
Returns the greatest or highest element in the set strictly less than the given element, or null if there is no such element.
T
pollFirst()
Removes and returns the least or lowest element in the set, or null if the map is empty.
T
pollLast()
Removes and returns the greatest or highest element in the set, or null if the map is empty.
boolean
remove(Object obj)
If the supplied Object is in this Set, it is removed, and true is returned; otherwise, false is returned.
int
size()
Returns the number of elements in this Set
SortedSet
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).
NavigableSet
subSet(T from, boolean fromInclusive, T to, boolean toInclusive)
Returns a view of this Set including all elements greater than (or equal to, if fromInclusive is true from and less than (or equal to, if toInclusive is true) to.
Comparator
super T> comparator()
Returns this Set's comparator.
SortedSet
tailSet(T from)
Returns a view of this Set including all elements greater or equal to from.
NavigableSet
tailSet(T from, boolean inclusive)
Returns a view of this Set including all elements greater (or equal to, if inclusive is true) from.

Methods inherited from class java.util.AbstractSet<E>

equals, hashCode, removeAll

Methods inherited from class java.util.AbstractCollection<E>

T[] toArray, add, addAll, clear, contains, containsAll, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toString

Methods inherited from class java.lang.Object

clone, equals, extends Object> getClass, finalize, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

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(SortedSet 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

TreeSet

public TreeSet(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(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

Method Details

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(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

ceiling

public T ceiling(T e)
Returns the least or lowest element in the set greater than or equal to the given element, or null if there is no such element.
Parameters:
e - the element relative to the returned element.
Returns:
the least element greater than or equal to the given element, or null if there is no such element.
Throws:
ClassCastException - if the specified element can not be compared with those in the map.
NullPointerException - if the element is null and this set either uses natural ordering or a comparator that does not permit null elements.
Since:
1.6

clear

public void clear()
Removes all elements in this Set.
Specified by:
clear in interface Set<E>
clear in interface Collection<E>
Overrides:
clear in interface AbstractCollection<E>

clone

public Object clone()
Returns a shallow copy of this Set. The elements are not cloned.
Overrides:
clone in interface Object
Returns:
the cloned set

contains

public boolean contains(Object obj)
Returns true if this Set contains the supplied Object, false otherwise.
Specified by:
contains in interface Set<E>
contains in interface Collection<E>
Overrides:
contains in interface AbstractCollection<E>
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

descendingIterator

public Iterator descendingIterator()
Returns an iterator over the elements of this set in descending order. This is equivalent to calling descendingSet().iterator().
Specified by:
descendingIterator in interface NavigableSet<E>
Returns:
an iterator over the elements in descending order.
Since:
1.6

descendingSet

public NavigableSet descendingSet()
Returns a view of the set in reverse order. The descending set is backed by the original set, so that changes affect both sets. Any changes occurring to either set while an iteration is taking place (with the exception of a Iterator.remove() operation) result in undefined behaviour from the iteration. The ordering of the descending set is the same as for a set with a Comparator given by Collections.reverseOrder(), and calling descendingSet() on the descending set itself results in a view equivalent to the original set.
Specified by:
descendingSet in interface NavigableSet<E>
Returns:
a reverse order view of the set.
Since:
1.6

first

public T first()
Returns the first (by order) element in this Set.
Specified by:
first in interface SortedSet<E>
Returns:
the first element
Throws:
NoSuchElementException - if the set is empty

floor

public T floor(T e)
Returns the greatest or highest element in the set less than or equal to the given element, or null if there is no such element.
Parameters:
e - the element relative to the returned element.
Returns:
the greatest element less than or equal to the given element, or null if there is no such element.
Throws:
ClassCastException - if the specified element can not be compared with those in the map.
NullPointerException - if the element is null and this set either uses natural ordering or a comparator that does not permit null elements.
Since:
1.6

headSet

public SortedSet 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 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 or call headSet(T,boolean). This call is equivalent to headSet(to, false).
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

headSet

public NavigableSet headSet(T to,
                               boolean inclusive)
Returns a view of this Set including all elements less than (or equal to, if inclusive is true) to. The returned set is backed by the original, so changes in one appear in the other. The subset will throw an IllegalArgumentException for any attempt to access or add an element beyond the specified cutoff.
Parameters:
to - the cutoff point
inclusive - true if to should be included.
Returns:
a view of the set for the specified range.
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

higher

public T higher(T e)
Returns the least or lowest element in the set strictly greater than the given element, or null if there is no such element.
Parameters:
e - the element relative to the returned element.
Returns:
the least element greater than the given element, or null if there is no such element.
Throws:
ClassCastException - if the specified element can not be compared with those in the map.
NullPointerException - if the element is null and this set either uses natural ordering or a comparator that does not permit null elements.
Since:
1.6

isEmpty

public boolean isEmpty()
Returns true if this Set has size 0, false otherwise.
Specified by:
isEmpty in interface Set<E>
isEmpty in interface Collection<E>
Overrides:
isEmpty in interface AbstractCollection<E>
Returns:
true if the set is empty

iterator

public Iterator iterator()
Returns in Iterator over the elements in this TreeSet, which traverses in ascending order.
Specified by:
iterator in interface NavigableSet<E>
iterator in interface Set<E>
iterator in interface Collection<E>
iterator in interface Iterable<E>
Overrides:
iterator in interface AbstractCollection<E>
Returns:
an iterator

last

public T last()
Returns the last (by order) element in this Set.
Specified by:
last in interface SortedSet<E>
Returns:
the last element
Throws:
NoSuchElementException - if the set is empty

lower

public T lower(T e)
Returns the greatest or highest element in the set strictly less than the given element, or null if there is no such element.
Parameters:
e - the element relative to the returned element.
Returns:
the greatest element less than the given element, or null if there is no such element.
Throws:
ClassCastException - if the specified element can not be compared with those in the map.
NullPointerException - if the element is null and this set either uses natural ordering or a comparator that does not permit null elements.
Since:
1.6

pollFirst

public T pollFirst()
Removes and returns the least or lowest element in the set, or null if the map is empty.
Specified by:
pollFirst in interface NavigableSet<E>
Returns:
the removed first element, or null if the map is empty.
Since:
1.6

pollLast

public T pollLast()
Removes and returns the greatest or highest element in the set, or null if the map is empty.
Specified by:
pollLast in interface NavigableSet<E>
Returns:
the removed last element, or null if the map is empty.
Since:
1.6

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.
Specified by:
remove in interface Set<E>
remove in interface Collection<E>
Overrides:
remove in interface AbstractCollection<E>
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
Specified by:
size in interface Set<E>
size in interface Collection<E>
Overrides:
size in interface AbstractCollection<E>
Returns:
the set size

subSet

public SortedSet 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 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 or call subSet(T,boolean,T,boolean). This is equivalent to calling subSet(from,true,to,false).
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

subSet

public NavigableSet subSet(T from,
                              boolean fromInclusive,
                              T to,
                              boolean toInclusive)
Returns a view of this Set including all elements greater than (or equal to, if fromInclusive is true from and less than (or equal to, if toInclusive is true) to. The returned set is backed by the original, so changes in one appear in the other. The subset will throw an IllegalArgumentException for any attempt to access or add an element beyond the specified cutoffs.
Parameters:
from - the low cutoff point
fromInclusive - true if from should be included.
to - the high cutoff point
toInclusive - true if to should be included.
Returns:
a view of the set for the specified range.
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

super T> comparator

public Comparatorsuper T> comparator()
Returns this Set's comparator.
Returns:
the comparator, or null if the set uses natural ordering

tailSet

public SortedSet 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 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 or call tailSet(T,boolean). This is equivalent to calling tailSet(from, true).
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

tailSet

public NavigableSet tailSet(T from,
                               boolean inclusive)
Returns a view of this Set including all elements greater (or equal to, if inclusive is true) from. The returned set is backed by the original, so changes in one appear in the other. The subset will throw an IllegalArgumentException for any attempt to access or add an element beyond the specified cutoff.
Parameters:
from - the low cutoff point.
inclusive - true if from should be included.
Returns:
a view of the set for the specified range.
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

TreeSet.java -- a class providing a TreeMap-backed SortedSet Copyright (C) 1999, 2000, 2001, 2004, 2005 Free Software Foundation, Inc. This file is part of GNU Classpath. GNU Classpath is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU Classpath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Classpath; see the file COPYING. If not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. Linking this library statically or dynamically with other modules is making a combined work based on this library. Thus, the terms and conditions of the GNU General Public License cover the whole combination. As a special exception, the copyright holders of this library give you permission to link this library with independent modules to produce an executable, regardless of the license terms of these independent modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.