TreeSet.java

package java.util;

public class TreeSet<E> extends AbstractSet<E>
    implements NavigableSet<E>, Cloneable, java.io.Serializable
{
    /**
     * 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.
     */
    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 {@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<E,Object>());
    }

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

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

    /**
     * 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
     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
     *
     * @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 {@code e} to this set if
     * the set contains no element {@code e2} such that
     * <tt>(e==null&nbsp;?&nbsp;e2==null&nbsp;:&nbsp;e.equals(e2))</tt>.
     * 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 {@code e} such that
     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>,
     * 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.
     */
    public void clear() {
        m.clear();
    }

    /**
     * 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<? 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);
    }

    /**
     * @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}
     * @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}
     * @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}
     * @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}
     * @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}
     * @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}
     */
    public E first() {
        return m.firstKey();
    }

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

    // NavigableSet API methods

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

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

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

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

    /**
     * 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 {@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
        Comparator<? super E> c = (Comparator<? super E>) s.readObject();

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

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

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

    private static final long serialVersionUID = -2479143000061671589L;
}