TreeSet

java.lang.Object
- java.util.AbstractCollection<E>
- - java.util.AbstractSet<T>
  - - java.util.TreeSet<T>

All Implemented Interfaces:

Cloneable, Iterable<T>, Collection<T>, NavigableSet<T>, Set<T>, SortedSet<T>
```
public class TreeSet<T>
extends AbstractSet<T>
implements NavigableSet<T>, Cloneable
```
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

Author:

Jon Zeppieri, Bryce McKinlay, Eric Blake (ebb9@email.byu.edu), Tom Tromey (tromey@redhat.com), Andrew John Hughes (gnu_andrew@member.fsf.org)

See Also:

Collection, Set, HashSet, LinkedHashSet, Comparable, Comparator, Collections.synchronizedSortedSet(SortedSet), TreeMap

Constructor Summary

Constructors
Constructor and Description
`TreeSet()` Construct a new TreeSet whose backing TreeMap using the "natural" ordering of keys.
`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(Comparator<? super T> comparator)` Construct a new TreeSet whose backing TreeMap uses the supplied Comparator.
`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

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`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(Collection<? extends 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.
`Comparator<? super T>`	`comparator()` Returns this Set's comparator.
`boolean`	`contains(Object obj)` Returns true if this Set contains the supplied Object, false otherwise.
`Iterator<T>`	`descendingIterator()` Returns an iterator over the elements of this set in descending order.
`NavigableSet<T>`	`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<T>`	`headSet(T to)` Returns a view of this Set including all elements less than `to`.
`NavigableSet<T>`	`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<T>`	`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
`NavigableSet<T>`	`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`.
`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`.
`NavigableSet<T>`	`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
equals, hashCode, removeAll

Methods inherited from class java.util.AbstractCollection
containsAll, retainAll, toArray, toArray, toString

Methods inherited from class java.lang.Object
getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Set
containsAll, equals, hashCode, removeAll, retainAll, toArray, toArray

- 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(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(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(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.
    
    Specified by:
    
    add in interface Collection<T>
    
    Specified by:
    
    add in interface Set<T>
    
    Overrides:
    
    add in class AbstractCollection<T>
    
    Parameters:
    
    obj - the Object to be added to this Set
    
    Returns:
    
    true if the add operation caused the Collection to change
    
    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.
    
    Specified by:
    
    addAll in interface Collection<T>
    
    Specified by:
    
    addAll in interface Set<T>
    
    Overrides:
    
    addAll in class AbstractCollection<T>
    
    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
    
    See Also:
    
    AbstractCollection.add(Object)
  - 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.
    
    Specified by:
    
    ceiling in interface NavigableSet<T>
    
    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 Collection<T>
    
    Specified by:
    
    clear in interface Set<T>
    
    Overrides:
    
    clear in class AbstractCollection<T>
    
    See Also:
    
    Iterator.remove()
  - 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.
    
    Specified by:
    
    comparator in interface SortedSet<T>
    
    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.
    
    Specified by:
    
    contains in interface Collection<T>
    
    Specified by:
    
    contains in interface Set<T>
    
    Overrides:
    
    contains in class AbstractCollection<T>
    
    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<T> 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<T>
    
    Returns:
    
    an iterator over the elements in descending order.
    
    Since:
    
    1.6
  - descendingSet
```
public NavigableSet<T> 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<T>
    
    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<T>
    
    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.
    
    Specified by:
    
    floor in interface NavigableSet<T>
    
    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<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 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).
    
    Specified by:
    
    headSet in interface NavigableSet<T>
    
    Specified by:
    
    headSet in interface SortedSet<T>
    
    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<T> 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.
    
    Specified by:
    
    headSet in interface NavigableSet<T>
    
    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.
    
    Specified by:
    
    higher in interface NavigableSet<T>
    
    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 Collection<T>
    
    Specified by:
    
    isEmpty in interface Set<T>
    
    Overrides:
    
    isEmpty in class AbstractCollection<T>
    
    Returns:
    
    true if the set is empty
    
    See Also:
    
    AbstractCollection.size()
  - iterator
```
public Iterator<T> iterator()
```
    Returns in Iterator over the elements in this TreeSet, which traverses in ascending order.
    
    Specified by:
    
    iterator in interface Iterable<T>
    
    Specified by:
    
    iterator in interface Collection<T>
    
    Specified by:
    
    iterator in interface NavigableSet<T>
    
    Specified by:
    
    iterator in interface Set<T>
    
    Specified by:
    
    iterator in class AbstractCollection<T>
    
    Returns:
    
    an iterator
  - last
```
public T last()
```
    Returns the last (by order) element in this Set.
    
    Specified by:
    
    last in interface SortedSet<T>
    
    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.
    
    Specified by:
    
    lower in interface NavigableSet<T>
    
    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<T>
    
    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<T>
    
    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 Collection<T>
    
    Specified by:
    
    remove in interface Set<T>
    
    Overrides:
    
    remove in class AbstractCollection<T>
    
    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
    
    See Also:
    
    Iterator.remove()
  - size
```
public int size()
```
    Returns the number of elements in this Set
    
    Specified by:
    
    size in interface Collection<T>
    
    Specified by:
    
    size in interface Set<T>
    
    Specified by:
    
    size in class AbstractCollection<T>
    
    Returns:
    
    the set size
  - subSet
```
public NavigableSet<T> 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.
    
    Specified by:
    
    subSet in interface NavigableSet<T>
    
    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
  - 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 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).
    
    Specified by:
    
    subSet in interface NavigableSet<T>
    
    Specified by:
    
    subSet in interface SortedSet<T>
    
    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 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).
    
    Specified by:
    
    tailSet in interface NavigableSet<T>
    
    Specified by:
    
    tailSet in interface SortedSet<T>
    
    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<T> 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.
    
    Specified by:
    
    tailSet in interface NavigableSet<T>
    
    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

Class TreeSet<T>

Constructor Summary

Method Summary

Methods inherited from class java.util.AbstractSet

Methods inherited from class java.util.AbstractCollection

Methods inherited from class java.lang.Object

Methods inherited from interface java.util.Set

Constructor Detail

TreeSet

TreeSet

TreeSet

TreeSet

Method Detail

add

addAll

ceiling

clear

clone

comparator

contains

descendingIterator

descendingSet

first

floor

headSet

headSet

higher

isEmpty

iterator

last

lower

pollFirst

pollLast

remove

size

subSet

subSet

tailSet

tailSet