TreeSetpublic 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. |
| Fields Summary |
|---|
| private transient NavigableMap | mThe backing map. | | private static final Object | PRESENT | | private static final long | serialVersionUID |
| Constructors Summary |
|---|
TreeSet(NavigableMap m)Constructs a set backed by the specified navigable map.
this.m = m;
| 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}.
this(new TreeMap<E,Object>());
| 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}.
this(new TreeMap<E,Object>(comparator));
| 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.
this();
addAll(c);
| public TreeSet(SortedSet s)Constructs a new tree set containing the same elements and
using the same ordering as the specified sorted set.
this(s.comparator());
addAll(s);
|
| Methods Summary |
|---|
| 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}.
return m.put(e, PRESENT)==null;
| | public boolean | addAll(java.util.Collection c)Adds all of the elements in the specified collection to this set.
// Use linear-time version if applicable
if (m.size()==0 && c.size() > 0 &&
c instanceof SortedSet &&
m instanceof TreeMap) {
SortedSet<? extends E> set = (SortedSet<? extends E>) c;
TreeMap<E,Object> map = (TreeMap<E, Object>) m;
Comparator<? super E> cc = (Comparator<? super E>) set.comparator();
Comparator<? super E> mc = map.comparator();
if (cc==mc || (cc != null && cc.equals(mc))) {
map.addAllForTreeSet(set, PRESENT);
return true;
}
}
return super.addAll(c);
| | public E | ceiling(E e)
return m.ceilingKey(e);
| | public void | clear()Removes all of the elements from this set.
The set will be empty after this call returns.
m.clear();
| | public java.lang.Object | clone()Returns a shallow copy of this {@code TreeSet} instance. (The elements
themselves are not cloned.)
TreeSet<E> clone = null;
try {
clone = (TreeSet<E>) super.clone();
} catch (CloneNotSupportedException e) {
throw new InternalError();
}
clone.m = new TreeMap<E,Object>(m);
return clone;
| | public java.util.Comparator | comparator()
return m.comparator();
| | public boolean | contains(java.lang.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)).
return m.containsKey(o);
| | public java.util.Iterator | descendingIterator()Returns an iterator over the elements in this set in descending order.
return m.descendingKeySet().iterator();
| | public java.util.NavigableSet | descendingSet()
return new TreeSet(m.descendingMap());
| | public E | first()
return m.firstKey();
| | public E | floor(E e)
return m.floorKey(e);
| | public java.util.NavigableSet | headSet(E toElement, boolean inclusive)
return new TreeSet<E>(m.headMap(toElement, inclusive));
| | public java.util.SortedSet | headSet(E toElement)
return headSet(toElement, false);
| | public E | higher(E e)
return m.higherKey(e);
| | public boolean | isEmpty()Returns {@code true} if this set contains no elements.
return m.isEmpty();
| | public java.util.Iterator | iterator()Returns an iterator over the elements in this set in ascending order.
return m.navigableKeySet().iterator();
| | public E | last()
return m.lastKey();
| | public E | lower(E e)
return m.lowerKey(e);
| | public E | pollFirst()
Map.Entry<E,?> e = m.pollFirstEntry();
return (e == null)? null : e.getKey();
| | public E | pollLast()
Map.Entry<E,?> e = m.pollLastEntry();
return (e == null)? null : e.getKey();
| | private void | readObject(java.io.ObjectInputStream s)Reconstitute the {@code TreeSet} instance from a stream (that is,
deserialize it).
// Read in any hidden stuff
s.defaultReadObject();
// Read in Comparator
Comparator<? super E> c = (Comparator<? super E>) s.readObject();
// Create backing TreeMap
TreeMap<E,Object> tm;
if (c==null)
tm = new TreeMap<E,Object>();
else
tm = new TreeMap<E,Object>(c);
m = tm;
// Read in size
int size = s.readInt();
tm.readTreeSet(size, s, PRESENT);
| | public boolean | remove(java.lang.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.)
return m.remove(o)==PRESENT;
| | public int | size()Returns the number of elements in this set (its cardinality).
return m.size();
| | public java.util.NavigableSet | subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive)
return new TreeSet<E>(m.subMap(fromElement, fromInclusive,
toElement, toInclusive));
| | public java.util.SortedSet | subSet(E fromElement, E toElement)
return subSet(fromElement, true, toElement, false);
| | public java.util.NavigableSet | tailSet(E fromElement, boolean inclusive)
return new TreeSet<E>(m.tailMap(fromElement, inclusive));
| | public java.util.SortedSet | tailSet(E fromElement)
return tailSet(fromElement, true);
| | private void | writeObject(java.io.ObjectOutputStream s)Save the state of the {@code TreeSet} instance to a stream (that is,
serialize it).
// Write out any hidden stuff
s.defaultWriteObject();
// Write out Comparator
s.writeObject(m.comparator());
// Write out size
s.writeInt(m.size());
// Write out all elements in the proper order.
for (Iterator i=m.keySet().iterator(); i.hasNext(); )
s.writeObject(i.next());
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