/*
 * Copyright (c) 1998, 2018, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.util;

A NavigableSet implementation based on a TreeMap. The elements are ordered using their 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 (add, remove and 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 Set interface. (See Comparable or Comparator for a precise definition of consistent with
equals.) This is so because the Set interface is defined in terms of the equals operation, but a TreeSet instance performs all element comparisons using its compareTo (or 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 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 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 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 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.
Author:
 Josh Bloch
Type parameters:
<E> – the type of elements maintained by this set
See Also:
Collection
Set
HashSet
Comparable
Comparator
TreeMap
Since:
  1.2/**
 * 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.
 *
 * <p>This implementation provides guaranteed log(n) time cost for the basic
 * operations ({@code add}, {@code remove} and {@code contains}).
 *
 * <p>Note that the ordering maintained by a set (whether or not an explicit
 * comparator is provided) must be <i>consistent with equals</i> if it is to
 * correctly implement the {@code Set} interface.  (See {@code Comparable}
 * or {@code Comparator} for a precise definition of <i>consistent with
 * equals</i>.)  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
 * <i>is</i> well-defined even if its ordering is inconsistent with equals; it
 * just fails to obey the general contract of the {@code Set} interface.
 *
 * <p><strong>Note that this implementation is not synchronized.</strong>
 * If multiple threads access a tree set concurrently, and at least one
 * of the threads modifies the set, it <i>must</i> 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: <pre>
 *   SortedSet s = Collections.synchronizedSortedSet(new TreeSet(...));</pre>
 *
 * <p>The iterators returned by this class's {@code iterator} method are
 * <i>fail-fast</i>: 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.
 *
 * <p>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:   <i>the fail-fast behavior of iterators
 * should be used only to detect bugs.</i>
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
 * Java Collections Framework</a>.
 *
 * @param <E> the type of elements maintained by this set
 *
 * @author  Josh Bloch
 * @see     Collection
 * @see     Set
 * @see     HashSet
 * @see     Comparable
 * @see     Comparator
 * @see     TreeMap
 * @since   1.2
 */

public class TreeSet<E> extends AbstractSet<E>
    implements NavigableSet<E>, Cloneable, java.io.Serializable
{
    
The backing map.
/**
     * The backing map.
     */
    private transient NavigableMap<E,Object> m;

    // Dummy value to associate with an Object in the backing Map
    private static final Object PRESENT = new Object();

    
Constructs a set backed by the specified navigable map.
/**
     * Constructs a set backed by the specified navigable map.
     */
    TreeSet(NavigableMap<E,Object> m) {
        this.m = m;
    }

    
Constructs a new, empty tree set, 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: e1.compareTo(e2) must not throw a ClassCastException for any elements e1 and 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 add call will throw a ClassCastException. /**
     * 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 <i>mutually
     * comparable</i>: {@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}.
     */
    public TreeSet() {
        this(new TreeMap<>());
    }

    
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: comparator.compare(e1,
e2) must not throw a ClassCastException for any elements e1 and e2 in the set. If the user attempts to add an element to the set that violates this constraint, the add call will throw a ClassCastException. 
Params:
comparator – the comparator that will be used to order this set. If null, the natural
       ordering of the elements will be used./**
     * Constructs a new, empty tree set, sorted according to the specified
     * comparator.  All elements inserted into the set must be <i>mutually
     * comparable</i> 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}.
     *
     * @param 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(Comparator<? super E> comparator) {
        this(new TreeMap<>(comparator));
    }

    
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: e1.compareTo(e2) must not throw a ClassCastException for any elements e1 and e2 in the set. 
Params:
c – collection whose elements will comprise the new set
Throws:
ClassCastException – if the elements in c are not Comparable, or are not mutually comparable
NullPointerException – if the specified collection is null/**
     * Constructs a new tree set containing the elements in the specified
     * collection, sorted according to the <i>natural ordering</i> of its
     * elements.  All elements inserted into the set must implement the
     * {@link Comparable} interface.  Furthermore, all such elements must be
     * <i>mutually comparable</i>: {@code e1.compareTo(e2)} must not throw a
     * {@code ClassCastException} for any elements {@code e1} and
     * {@code e2} in the set.
     *
     * @param c collection whose elements will comprise the new set
     * @throws ClassCastException if the elements in {@code c} are
     *         not {@link Comparable}, or are not mutually comparable
     * @throws NullPointerException if the specified collection is null
     */
    public TreeSet(Collection<? extends E> c) {
        this();
        addAll(c);
    }

    
Constructs a new tree set containing the same elements and
using the same ordering as the specified sorted set.
Params:
s – sorted set whose elements will comprise the new set
Throws:
NullPointerException – if the specified sorted set is null/**
     * Constructs a new tree set containing the same elements and
     * using the same ordering as the specified sorted set.
     *
     * @param s sorted set whose elements will comprise the new set
     * @throws NullPointerException if the specified sorted set is null
     */
    public TreeSet(SortedSet<E> s) {
        this(s.comparator());
        addAll(s);
    }

    
Returns an iterator over the elements in this set in ascending order.
Returns:
an iterator over the elements in this set in ascending order/**
     * Returns an iterator over the elements in this set in ascending order.
     *
     * @return an iterator over the elements in this set in ascending order
     */
    public Iterator<E> iterator() {
        return m.navigableKeySet().iterator();
    }

    
Returns an iterator over the elements in this set in descending order.
Returns:
an iterator over the elements in this set in descending order
Since:
1.6/**
     * Returns an iterator over the elements in this set in descending order.
     *
     * @return an iterator over the elements in this set in descending order
     * @since 1.6
     */
    public Iterator<E> descendingIterator() {
        return m.descendingKeySet().iterator();
    }

    
Since:
1.6/**
     * @since 1.6
     */
    public NavigableSet<E> descendingSet() {
        return new TreeSet<>(m.descendingMap());
    }

    
Returns the number of elements in this set (its cardinality).
Returns:
the number of elements in this set (its cardinality)/**
     * Returns the number of elements in this set (its cardinality).
     *
     * @return the number of elements in this set (its cardinality)
     */
    public int size() {
        return m.size();
    }

    
Returns true if this set contains no elements. 
Returns:
true if this set contains no elements/**
     * Returns {@code true} if this set contains no elements.
     *
     * @return {@code true} if this set contains no elements
     */
    public boolean isEmpty() {
        return m.isEmpty();
    }

    
Returns true if this set contains the specified element. More formally, returns true if and only if this set contains an element e such that Objects.equals(o, e). 
Params:
o – object to be checked for containment in this set
Throws:
ClassCastException – if the specified object cannot be compared
        with the elements currently in the set
NullPointerException – if the specified element is null
        and this set uses natural ordering, or its comparator
        does not permit null elements
Returns:
true if this set contains the specified element/**
     * 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
     * {@code Objects.equals(o, e)}.
     *
     * @param o object to be checked for containment in this set
     * @return {@code true} if this set contains the specified element
     * @throws ClassCastException if the specified object cannot be compared
     *         with the elements currently in the set
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     */
    public boolean contains(Object o) {
        return m.containsKey(o);
    }

    
Adds the specified element to this set if it is not already present. More formally, adds the specified element e to this set if the set contains no element e2 such that Objects.equals(e, e2). If this set already contains the element, the call leaves the set unchanged and returns false. 
Params:
e – element to be added to this set
Throws:
ClassCastException – if the specified object cannot be compared
        with the elements currently in this set
NullPointerException – if the specified element is null
        and this set uses natural ordering, or its comparator
        does not permit null elements
Returns:
true if this set did not already contain the specified element/**
     * 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
     * {@code Objects.equals(e, e2)}.
     * If this set already contains the element, the call leaves the set
     * unchanged and returns {@code false}.
     *
     * @param e element to be added to this set
     * @return {@code true} if this set did not already contain the specified
     *         element
     * @throws ClassCastException if the specified object cannot be compared
     *         with the elements currently in this set
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     */
    public boolean add(E e) {
        return m.put(e, PRESENT)==null;
    }

    
Removes the specified element from this set if it is present. More formally, removes an element e such that Objects.equals(o, e), if this set contains such an element. Returns 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.) 
Params:
o – object to be removed from this set, if present
Throws:
ClassCastException – if the specified object cannot be compared
        with the elements currently in this set
NullPointerException – if the specified element is null
        and this set uses natural ordering, or its comparator
        does not permit null elements
Returns:
true if this set contained the specified element/**
     * Removes the specified element from this set if it is present.
     * More formally, removes an element {@code e} such that
     * {@code Objects.equals(o, 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.)
     *
     * @param o object to be removed from this set, if present
     * @return {@code true} if this set contained the specified element
     * @throws ClassCastException if the specified object cannot be compared
     *         with the elements currently in this set
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     */
    public boolean remove(Object o) {
        return m.remove(o)==PRESENT;
    }

    
Removes all of the elements from this set.
The set will be empty after this call returns.
/**
     * Removes all of the elements from this set.
     * The set will be empty after this call returns.
     */
    public void clear() {
        m.clear();
    }

    
Adds all of the elements in the specified collection to this set.
Params:
c – collection containing elements to be added to this set
Throws:
ClassCastException – if the elements provided cannot be compared
        with the elements currently in the set
NullPointerException – if the specified collection is null or
        if any element is null and this set uses natural ordering, or
        its comparator does not permit null elements
Returns:
true if this set changed as a result of the call/**
     * Adds all of the elements in the specified collection to this set.
     *
     * @param c collection containing elements to be added to this set
     * @return {@code true} if this set changed as a result of the call
     * @throws ClassCastException if the elements provided cannot be compared
     *         with the elements currently in the set
     * @throws NullPointerException if the specified collection is null or
     *         if any element is null and this set uses natural ordering, or
     *         its comparator does not permit null elements
     */
    public  boolean addAll(Collection<? extends E> c) {
        // 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<?> cc = 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);
    }

    
Throws:
ClassCastException – {@inheritDoc}
NullPointerException – if fromElement or toElement is null and this set uses natural ordering, or its comparator does not permit null elements
IllegalArgumentException – {@inheritDoc}
Since:
1.6/**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if {@code fromElement} or {@code toElement}
     *         is null and this set uses natural ordering, or its comparator
     *         does not permit null elements
     * @throws IllegalArgumentException {@inheritDoc}
     * @since 1.6
     */
    public NavigableSet<E> subSet(E fromElement, boolean fromInclusive,
                                  E toElement,   boolean toInclusive) {
        return new TreeSet<>(m.subMap(fromElement, fromInclusive,
                                       toElement,   toInclusive));
    }

    
Throws:
ClassCastException – {@inheritDoc}
NullPointerException – if toElement is null and this set uses natural ordering, or its comparator does not permit null elements
IllegalArgumentException – {@inheritDoc}
Since:
1.6/**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if {@code toElement} is null and
     *         this set uses natural ordering, or its comparator does
     *         not permit null elements
     * @throws IllegalArgumentException {@inheritDoc}
     * @since 1.6
     */
    public NavigableSet<E> headSet(E toElement, boolean inclusive) {
        return new TreeSet<>(m.headMap(toElement, inclusive));
    }

    
Throws:
ClassCastException – {@inheritDoc}
NullPointerException – if fromElement is null and this set uses natural ordering, or its comparator does not permit null elements
IllegalArgumentException – {@inheritDoc}
Since:
1.6/**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if {@code fromElement} is null and
     *         this set uses natural ordering, or its comparator does
     *         not permit null elements
     * @throws IllegalArgumentException {@inheritDoc}
     * @since 1.6
     */
    public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
        return new TreeSet<>(m.tailMap(fromElement, inclusive));
    }

    
Throws:
ClassCastException – {@inheritDoc}
NullPointerException – if fromElement or toElement is null and this set uses natural ordering, or its comparator does not permit null elements
IllegalArgumentException – {@inheritDoc}/**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if {@code fromElement} or
     *         {@code toElement} is null and this set uses natural ordering,
     *         or its comparator does not permit null elements
     * @throws IllegalArgumentException {@inheritDoc}
     */
    public SortedSet<E> subSet(E fromElement, E toElement) {
        return subSet(fromElement, true, toElement, false);
    }

    
Throws:
ClassCastException – {@inheritDoc}
NullPointerException – if toElement is null and this set uses natural ordering, or its comparator does not permit null elements
IllegalArgumentException – {@inheritDoc}/**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if {@code toElement} is null
     *         and this set uses natural ordering, or its comparator does
     *         not permit null elements
     * @throws IllegalArgumentException {@inheritDoc}
     */
    public SortedSet<E> headSet(E toElement) {
        return headSet(toElement, false);
    }

    
Throws:
ClassCastException – {@inheritDoc}
NullPointerException – if fromElement is null and this set uses natural ordering, or its comparator does not permit null elements
IllegalArgumentException – {@inheritDoc}/**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if {@code fromElement} is null
     *         and this set uses natural ordering, or its comparator does
     *         not permit null elements
     * @throws IllegalArgumentException {@inheritDoc}
     */
    public SortedSet<E> tailSet(E fromElement) {
        return tailSet(fromElement, true);
    }

    public Comparator<? super E> comparator() {
        return m.comparator();
    }

    
Throws:
NoSuchElementException – {@inheritDoc}/**
     * @throws NoSuchElementException {@inheritDoc}
     */
    public E first() {
        return m.firstKey();
    }

    
Throws:
NoSuchElementException – {@inheritDoc}/**
     * @throws NoSuchElementException {@inheritDoc}
     */
    public E last() {
        return m.lastKey();
    }

    // NavigableSet API methods

    
Throws:
ClassCastException – {@inheritDoc}
NullPointerException – if the specified element is null
        and this set uses natural ordering, or its comparator
        does not permit null elements
Since:
1.6/**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     * @since 1.6
     */
    public E lower(E e) {
        return m.lowerKey(e);
    }

    
Throws:
ClassCastException – {@inheritDoc}
NullPointerException – if the specified element is null
        and this set uses natural ordering, or its comparator
        does not permit null elements
Since:
1.6/**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     * @since 1.6
     */
    public E floor(E e) {
        return m.floorKey(e);
    }

    
Throws:
ClassCastException – {@inheritDoc}
NullPointerException – if the specified element is null
        and this set uses natural ordering, or its comparator
        does not permit null elements
Since:
1.6/**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     * @since 1.6
     */
    public E ceiling(E e) {
        return m.ceilingKey(e);
    }

    
Throws:
ClassCastException – {@inheritDoc}
NullPointerException – if the specified element is null
        and this set uses natural ordering, or its comparator
        does not permit null elements
Since:
1.6/**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     * @since 1.6
     */
    public E higher(E e) {
        return m.higherKey(e);
    }

    
Since:
1.6/**
     * @since 1.6
     */
    public E pollFirst() {
        Map.Entry<E,?> e = m.pollFirstEntry();
        return (e == null) ? null : e.getKey();
    }

    
Since:
1.6/**
     * @since 1.6
     */
    public E pollLast() {
        Map.Entry<E,?> e = m.pollLastEntry();
        return (e == null) ? null : e.getKey();
    }

    
Returns a shallow copy of this TreeSet instance. (The elements themselves are not cloned.) 
Returns:
a shallow copy of this set/**
     * Returns a shallow copy of this {@code TreeSet} instance. (The elements
     * themselves are not cloned.)
     *
     * @return a shallow copy of this set
     */
    @SuppressWarnings("unchecked")
    public Object clone() {
        TreeSet<E> clone;
        try {
            clone = (TreeSet<E>) super.clone();
        } catch (CloneNotSupportedException e) {
            throw new InternalError(e);
        }

        clone.m = new TreeMap<>(m);
        return clone;
    }

    
Save the state of the TreeSet instance to a stream (that is, serialize it). 
@serialData
Emits the comparator used to order this set, or null if it obeys its elements' natural ordering (Object), followed by the size of the set (the number of elements it contains) (int), followed by all of its elements (each an Object) in order (as determined by the set's Comparator, or by the elements' natural ordering if the set has no Comparator)./**
     * Save the state of the {@code TreeSet} instance to a stream (that is,
     * serialize it).
     *
     * @serialData Emits the comparator used to order this set, or
     *             {@code null} if it obeys its elements' natural ordering
     *             (Object), followed by the size of the set (the number of
     *             elements it contains) (int), followed by all of its
     *             elements (each an Object) in order (as determined by the
     *             set's Comparator, or by the elements' natural ordering if
     *             the set has no Comparator).
     */
    private void writeObject(java.io.ObjectOutputStream s)
        throws java.io.IOException {
        // 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 (E e : m.keySet())
            s.writeObject(e);
    }

    
Reconstitute the TreeSet instance from a stream (that is, deserialize it). /**
     * Reconstitute the {@code TreeSet} instance from a stream (that is,
     * deserialize it).
     */
    private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {
        // Read in any hidden stuff
        s.defaultReadObject();

        // Read in Comparator
        @SuppressWarnings("unchecked")
            Comparator<? super E> c = (Comparator<? super E>) s.readObject();

        // Create backing TreeMap
        TreeMap<E,Object> tm = new TreeMap<>(c);
        m = tm;

        // Read in size
        int size = s.readInt();

        tm.readTreeSet(size, s, PRESENT);
    }

    
Creates a late-binding
and fail-fast Spliterator over the elements in this set. 
The Spliterator reports Spliterator.SIZED, Spliterator.DISTINCT, Spliterator.SORTED, and Spliterator.ORDERED. Overriding implementations should document the reporting of additional characteristic values. 
The spliterator's comparator (see Spliterator.getComparator()) is null if the tree set's comparator (see comparator()) is null. Otherwise, the spliterator's comparator is the same as or imposes the same total ordering as the tree set's comparator. 
Returns:
a Spliterator over the elements in this set
Since:
1.8/**
     * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
     * and <em>fail-fast</em> {@link Spliterator} over the elements in this
     * set.
     *
     * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
     * {@link Spliterator#DISTINCT}, {@link Spliterator#SORTED}, and
     * {@link Spliterator#ORDERED}.  Overriding implementations should document
     * the reporting of additional characteristic values.
     *
     * <p>The spliterator's comparator (see
     * {@link java.util.Spliterator#getComparator()}) is {@code null} if
     * the tree set's comparator (see {@link #comparator()}) is {@code null}.
     * Otherwise, the spliterator's comparator is the same as or imposes the
     * same total ordering as the tree set's comparator.
     *
     * @return a {@code Spliterator} over the elements in this set
     * @since 1.8
     */
    public Spliterator<E> spliterator() {
        return TreeMap.keySpliteratorFor(m);
    }

    private static final long serialVersionUID = -2479143000061671589L;
}