TreeSet.java

/* TreeSet.java -- a class providing a TreeMap-backed SortedSet
   Copyright (C) 1999, 2000, 2001, 2004, 2005 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

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WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
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terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
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this exception to your version of the library, but you are not
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package java.util;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

/**
 * This class provides a TreeMap-backed implementation of the SortedSet
 * interface. The elements will be sorted according to their <i>natural
 * order</i>, or according to the provided <code>Comparator</code>.<p>
 *
 * Most operations are O(log n), but there is so much overhead that this
 * makes small sets expensive. Note that the ordering must be <i>consistent
 * with equals</i> 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.<p>
 *
 * This implementation is not synchronized. If you need to share this between
 * multiple threads, do something like:<br>
 * <code>SortedSet s
 *       = Collections.synchronizedSortedSet(new TreeSet(...));</code><p>
 *
 * The iterators are <i>fail-fast</i>, meaning that any structural
 * modification, except for <code>remove()</code> called on the iterator
 * itself, cause the iterator to throw a
 * <code>ConcurrentModificationException</code> rather than exhibit
 * non-deterministic behavior.
 *
 * @author Jon Zeppieri
 * @author Bryce McKinlay
 * @author Eric Blake (ebb9@email.byu.edu)
 * @author Tom Tromey (tromey@redhat.com)
 * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
 * @see Collection
 * @see Set
 * @see HashSet
 * @see LinkedHashSet
 * @see Comparable
 * @see Comparator
 * @see Collections#synchronizedSortedSet(SortedSet)
 * @see TreeMap
 * @since 1.2
 * @status updated to 1.6
 */
public class TreeSet<T> extends AbstractSet<T>
  implements NavigableSet<T>, Cloneable, Serializable
{
  /**
   * Compatible with JDK 1.2.
   */
  private static final long serialVersionUID = -2479143000061671589L;

  /**
   * The NavigableMap which backs this Set.
   */
  // Not final because of readObject. This will always be one of TreeMap or
  // TreeMap.SubMap, which both extend AbstractMap.
  private transient NavigableMap<T, String> map;

  /**
   * 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 Comparable
   */
  public TreeSet()
  {
    map = new TreeMap<T, String>();
  }

  /**
   * Construct a new TreeSet whose backing TreeMap uses the supplied
   * Comparator. Elements that are not mutually comparable will cause
   * ClassCastExceptions down the road.
   *
   * @param comparator the Comparator this Set will use
   */
  public TreeSet(Comparator<? super T> comparator)
  {
    map = new TreeMap<T, String>(comparator);
  }

  /**
   * 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.
   *
   * @param 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
   * @throws NullPointerException if the collection is null
   * @see Comparable
   */
  public TreeSet(Collection<? extends T> collection)
  {
    map = new TreeMap<T, String>();
    addAll(collection);
  }

  /**
   * 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.
   *
   * @param sortedSet the new TreeSet will use this SortedSet's comparator
   *        and will initialize itself with all its elements
   * @throws NullPointerException if sortedSet is null
   */
  public TreeSet(SortedSet<T> sortedSet)
  {
    Iterator<T> itr;

    map = new TreeMap<T, String>
      ((Comparator<? super T>)sortedSet.comparator());
    itr = ((SortedSet<T>) sortedSet).iterator();
    ((TreeMap<T, String>) map).putKeysLinear(itr, sortedSet.size());
  }

  /**
   * This private constructor is used to implement the subSet() calls around
   * a backing TreeMap.SubMap.
   *
   * @param backingMap the submap
   */
  private TreeSet(NavigableMap<T,String> backingMap)
  {
    map = backingMap;
  }

  /**
   * Adds the spplied Object to the Set if it is not already in the Set;
   * returns true if the element is added, false otherwise.
   *
   * @param obj the Object to be added to this Set
   * @throws ClassCastException if the element cannot be compared with objects
   *         already in the set
   */
  public boolean add(T obj)
  {
    return map.put(obj, "") == null;
  }

  /**
   * Adds all of the elements in the supplied Collection to this TreeSet.
   *
   * @param c The collection to add
   * @return true if the Set is altered, false otherwise
   * @throws NullPointerException if c is null
   * @throws ClassCastException if an element in c cannot be compared with
   *         objects already in the set
   */
  public boolean addAll(Collection<? extends T> c)
  {
    boolean result = false;
    int pos = c.size();
    Iterator<? extends T> itr = c.iterator();
    while (--pos >= 0)
      result |= (map.put(itr.next(), "") == null);
    return result;
  }

  /**
   * Removes all elements in this Set.
   */
  public void clear()
  {
    map.clear();
  }

  /**
   * Returns a shallow copy of this Set. The elements are not cloned.
   *
   * @return the cloned set
   */
  public Object clone()
  {
    TreeSet<T> copy = null;
    try
      {
        copy = (TreeSet<T>) super.clone();
        // Map may be either TreeMap or TreeMap.SubMap, hence the ugly casts.
        copy.map = (NavigableMap<T, String>) ((AbstractMap<T, String>) map).clone();
      }
    catch (CloneNotSupportedException x)
      {
        // Impossible result.
      }
    return copy;
  }

  /**
   * Returns this Set's comparator.
   *
   * @return the comparator, or null if the set uses natural ordering
   */
  public Comparator<? super T> comparator()
  {
    return map.comparator();
  }

  /**
   * Returns true if this Set contains the supplied Object, false otherwise.
   *
   * @param obj the Object to check for
   * @return true if it is in the set
   * @throws ClassCastException if obj cannot be compared with objects
   *         already in the set
   */
  public boolean contains(Object obj)
  {
    return map.containsKey(obj);
  }

  /**
   * Returns the first (by order) element in this Set.
   *
   * @return the first element
   * @throws NoSuchElementException if the set is empty
   */
  public T first()
  {
    return map.firstKey();
  }

  /**
   * Returns a view of this Set including all elements less than
   * <code>to</code>. The returned set is backed by the original, so changes
   * in one appear in the other. The subset will throw an
   * {@link 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 {@link #headSet(T,boolean)}.  This call is equivalent to
   * <code>headSet(to, false)</code>.
   *
   * @param to the (exclusive) cutoff point
   * @return a view of the set less than the cutoff
   * @throws ClassCastException if <code>to</code> is not compatible with
   *         the comparator (or is not Comparable, for natural ordering)
   * @throws NullPointerException if to is null, but the comparator does not
   *         tolerate null elements
   */
  public SortedSet<T> headSet(T to)
  {
    return headSet(to, false);
  }

  /**
   * Returns a view of this Set including all elements less than
   * (or equal to, if <code>inclusive</code> is true) <code>to</code>.
   * The returned set is backed by the original, so changes
   * in one appear in the other. The subset will throw an
   * {@link IllegalArgumentException} for any attempt to access or add an
   * element beyond the specified cutoff. 
   *
   * @param to the cutoff point
   * @param inclusive true if <code>to</code> should be included.
   * @return a view of the set for the specified range.
   * @throws ClassCastException if <code>to</code> is not compatible with
   *         the comparator (or is not Comparable, for natural ordering)
   * @throws NullPointerException if to is null, but the comparator does not
   *         tolerate null elements
   */
  public NavigableSet<T> headSet(T to, boolean inclusive)
  {
    return new TreeSet<T>(map.headMap(to, inclusive));
  }

  /**
   * Returns true if this Set has size 0, false otherwise.
   *
   * @return true if the set is empty
   */
  public boolean isEmpty()
  {
    return map.isEmpty();
  }

  /**
   * Returns in Iterator over the elements in this TreeSet, which traverses
   * in ascending order.
   *
   * @return an iterator
   */
  public Iterator<T> iterator()
  {
    return map.keySet().iterator();
  }

  /**
   * Returns the last (by order) element in this Set.
   *
   * @return the last element
   * @throws NoSuchElementException if the set is empty
   */
  public T last()
  {
    return map.lastKey();
  }

  /**
   * If the supplied Object is in this Set, it is removed, and true is
   * returned; otherwise, false is returned.
   *
   * @param obj the Object to remove from this Set
   * @return true if the set was modified
   * @throws ClassCastException if obj cannot be compared to set elements
   */
  public boolean remove(Object obj)
  {
    return map.remove(obj) != null;
  }

  /**
   * Returns the number of elements in this Set
   *
   * @return the set size
   */
  public int size()
  {
    return map.size();
  }

  /**
   * Returns a view of this Set including all elements greater or equal to
   * <code>from</code> and less than <code>to</code> (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 {@link 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 {@link #subSet(T,boolean,T,boolean)}.  This is equivalent to
   * calling <code>subSet(from,true,to,false)</code>.
   *
   * @param from the (inclusive) low cutoff point
   * @param to the (exclusive) high cutoff point
   * @return 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)
   * @throws NullPointerException if from or to is null, but the comparator
   *         does not tolerate null elements
   * @throws IllegalArgumentException if from is greater than to
   */
  public SortedSet<T> subSet(T from, T to)
  {
    return subSet(from, true, to, false);
  }

  /**
   * Returns a view of this Set including all elements greater than (or equal to,
   * if <code>fromInclusive</code> is true</code> <code>from</code> and less than
   * (or equal to, if <code>toInclusive</code> is true) <code>to</code>.
   * The returned set is backed by the original, so changes in one appear in
   * the other. The subset will throw an {@link IllegalArgumentException}
   * for any attempt to access or add an element beyond the specified cutoffs.
   *
   * @param from the low cutoff point
   * @param fromInclusive true if <code>from</code> should be included.
   * @param to the high cutoff point
   * @param toInclusive true if <code>to</code> should be included.
   * @return 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)
   * @throws NullPointerException if from or to is null, but the comparator
   *         does not tolerate null elements
   * @throws IllegalArgumentException if from is greater than to
   */
  public NavigableSet<T> subSet(T from, boolean fromInclusive,
				T to, boolean toInclusive)
  {
    return new TreeSet<T>(map.subMap(from, fromInclusive,
				     to, toInclusive));
  }

  /**
   * Returns a view of this Set including all elements greater or equal to
   * <code>from</code>. The returned set is backed by the original, so
   * changes in one appear in the other. The subset will throw an
   * {@link 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 {@link #tailSet(T,boolean)}.  This is equivalent to calling
   * <code>tailSet(from, true)</code>.
   *
   * @param from the (inclusive) low cutoff point
   * @return a view of the set above the cutoff
   * @throws ClassCastException if <code>from</code> is not compatible with
   *         the comparator (or is not Comparable, for natural ordering)
   * @throws NullPointerException if from is null, but the comparator
   *         does not tolerate null elements
   */
  public SortedSet<T> tailSet(T from)
  {
    return tailSet(from, true);
  }

  /**
   * Returns a view of this Set including all elements greater (or equal to,
   * if <code>inclusive</code> is true) <code>from</code>. The returned set
   * is backed by the original, so changes in one appear in the other. The
   * subset will throw an {@link IllegalArgumentException} for any attempt
   * to access or add an element beyond the specified cutoff.
   *
   * @param from the low cutoff point.
   * @param inclusive true if <code>from</code> should be included.
   * @return a view of the set for the specified range.
   * @throws ClassCastException if <code>from</code> is not compatible with
   *         the comparator (or is not Comparable, for natural ordering)
   * @throws NullPointerException if from is null, but the comparator
   *         does not tolerate null elements
   */
  public NavigableSet<T> tailSet(T from, boolean inclusive)
  {
    return new TreeSet<T>(map.tailMap(from, inclusive));
  }

  /**
   * Serializes this object to the given stream.
   *
   * @param s the stream to write to
   * @throws IOException if the underlying stream fails
   * @serialData the <i>comparator</i> (Object), followed by the set size
   *             (int), the the elements in sorted order (Object)
   */
  private void writeObject(ObjectOutputStream s) throws IOException
  {
    s.defaultWriteObject();
    Iterator<T> itr = map.keySet().iterator();
    int pos = map.size();
    s.writeObject(map.comparator());
    s.writeInt(pos);
    while (--pos >= 0)
      s.writeObject(itr.next());
  }

  /**
   * Deserializes this object from the given stream.
   *
   * @param s the stream to read from
   * @throws ClassNotFoundException if the underlying stream fails
   * @throws IOException if the underlying stream fails
   * @serialData the <i>comparator</i> (Object), followed by the set size
   *             (int), the the elements in sorted order (Object)
   */
  private void readObject(ObjectInputStream s)
    throws IOException, ClassNotFoundException
  {
    s.defaultReadObject();
    Comparator<? super T> comparator = (Comparator<? super T>) s.readObject();
    int size = s.readInt();
    map = new TreeMap<T, String>(comparator);
    ((TreeMap<T, String>) map).putFromObjStream(s, size, false);
  }

  /**
   * Returns the least or lowest element in the set greater than or
   * equal to the given element, or <code>null</code> if there is
   * no such element.
   *
   * @param e the element relative to the returned element.
   * @return the least element greater than or equal
   *         to the given element, or <code>null</code> if there is
   *         no such element.
   * @throws ClassCastException if the specified element can not
   *                            be compared with those in the map.
   * @throws NullPointerException if the element is <code>null</code>
   *                              and this set either uses natural
   *                              ordering or a comparator that does
   *                              not permit null elements.
   * @since 1.6
   */
  public T ceiling(T e)
  {
    return map.ceilingKey(e);
  }

  /**
   * Returns an iterator over the elements of this set in descending
   * order.  This is equivalent to calling
   * <code>descendingSet().iterator()</code>.
   *
   * @return an iterator over the elements in descending order.
   * @since 1.6
   */
  public Iterator<T> descendingIterator()
  {
    return descendingSet().iterator();
  }

  /**
   * 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 {@link 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
   * {@link Comparator} given by {@link Collections#reverseOrder()},
   * and calling {@link #descendingSet()} on the descending set itself
   * results in a view equivalent to the original set.
   *
   * @return a reverse order view of the set.
   * @since 1.6
   */
  public NavigableSet<T> descendingSet()
  {
    return map.descendingKeySet();
  }

  /**
   * Returns the greatest or highest element in the set less than or
   * equal to the given element, or <code>null</code> if there is
   * no such element.
   *
   * @param e the element relative to the returned element.
   * @return the greatest element less than or equal
   *         to the given element, or <code>null</code> if there is
   *         no such element.
   * @throws ClassCastException if the specified element can not
   *                            be compared with those in the map.
   * @throws NullPointerException if the element is <code>null</code>
   *                              and this set either uses natural
   *                              ordering or a comparator that does
   *                              not permit null elements.
   * @since 1.6
   */
  public T floor(T e)
  {
    return map.floorKey(e);
  }

  /**
   * Returns the least or lowest element in the set strictly greater
   * than the given element, or <code>null</code> if there is
   * no such element.
   *
   * @param e the element relative to the returned element.
   * @return the least element greater than 
   *         the given element, or <code>null</code> if there is
   *         no such element.
   * @throws ClassCastException if the specified element can not
   *                            be compared with those in the map.
   * @throws NullPointerException if the element is <code>null</code>
   *                              and this set either uses natural
   *                              ordering or a comparator that does
   *                              not permit null elements.
   * @since 1.6
   */
  public T higher(T e)
  {
    return map.higherKey(e);
  }

  /**
   * Returns the greatest or highest element in the set strictly less
   * than the given element, or <code>null</code> if there is
   * no such element.
   *
   * @param e the element relative to the returned element.
   * @return the greatest element less than 
   *         the given element, or <code>null</code> if there is
   *         no such element.
   * @throws ClassCastException if the specified element can not
   *                            be compared with those in the map.
   * @throws NullPointerException if the element is <code>null</code>
   *                              and this set either uses natural
   *                              ordering or a comparator that does
   *                              not permit null elements.
   * @since 1.6
   */
  public T lower(T e)
  {
    return map.lowerKey(e);
  }

  /**
   * Removes and returns the least or lowest element in the set,
   * or <code>null</code> if the map is empty.
   *
   * @return the removed first element, or <code>null</code> if the
   *         map is empty.
   * @since 1.6
   */
  public T pollFirst()
  {
    return map.pollFirstEntry().getKey();
  }

  /**
   * Removes and returns the greatest or highest element in the set,
   * or <code>null</code> if the map is empty.
   *
   * @return the removed last element, or <code>null</code> if the
   *         map is empty.
   * @since 1.6
   */
  public T pollLast()
  {
    return map.pollLastEntry().getKey();
  }

}