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public class: TreeSet [javadoc | source]

All Implemented Interfaces:
    Cloneable, NavigableSet, java$io$Serializable, Set, Collection

Direct Known Subclasses:

A NavigableSet implementation based on a TreeMap . The elements are ordered using their {@linkplain Comparable 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 ({@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 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 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.

 public TreeSet() 
 TreeSet(NavigableMap<E, Object> m) 
    Constructs a set backed by the specified navigable map.
 public TreeSet(Comparator<? super E> 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}.
    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.
 public 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. All elements inserted into the set must implement the 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.
    c - collection whose elements will comprise the new set
    ClassCastException - if the elements in {@code c} are not Comparable , or are not mutually comparable
    NullPointerException - if the specified collection is null
 public TreeSet(SortedSet<E> s) 
    Constructs a new tree set containing the same elements and using the same ordering as the specified sorted set.
    s - sorted set whose elements will comprise the new set
    NullPointerException - if the specified sorted set is null
Method from java.util.TreeSet Summary:
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
Methods from java.util.AbstractSet:
equals,   hashCode,   removeAll
Methods from java.util.AbstractCollection:
add,   addAll,   clear,   contains,   containsAll,   isEmpty,   iterator,   remove,   removeAll,   retainAll,   size,   toArray,   toArray,   toString
Methods from java.lang.Object:
clone,   equals,   finalize,   getClass,   hashCode,   notify,   notifyAll,   toString,   wait,   wait,   wait
Method from java.util.TreeSet Detail:
 public boolean add(E 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}.
 public boolean addAll(Collection<? extends E> c) 
    Adds all of the elements in the specified collection to this set.
 public E ceiling(E e) 
 public  void clear() 
    Removes all of the elements from this set. The set will be empty after this call returns.
 public Object clone() 
    Returns a shallow copy of this {@code TreeSet} instance. (The elements themselves are not cloned.)
 public Comparator<? super E> comparator() 
 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)).
 public Iterator<E> descendingIterator() 
    Returns an iterator over the elements in this set in descending order.
 public NavigableSet<E> descendingSet() 
 public E first() 
 public E floor(E e) 
 public SortedSet<E> headSet(E toElement) 
 public NavigableSet<E> headSet(E toElement,
    boolean inclusive) 
 public E higher(E e) 
 public boolean isEmpty() 
    Returns {@code true} if this set contains no elements.
 public Iterator<E> iterator() 
    Returns an iterator over the elements in this set in ascending order.
 public E last() 
 public E lower(E e) 
 public E pollFirst() 
 public E pollLast() 
 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.)
 public int size() 
    Returns the number of elements in this set (its cardinality).
 public SortedSet<E> subSet(E fromElement,
    E toElement) 
 public NavigableSet<E> subSet(E fromElement,
    boolean fromInclusive,
    E toElement,
    boolean toInclusive) 
 public SortedSet<E> tailSet(E fromElement) 
 public NavigableSet<E> tailSet(E fromElement,
    boolean inclusive)