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/*
 * Copyright 2008 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package java.util;

import static com.google.gwt.core.shared.impl.InternalPreconditions.checkNotNull;

import java.io.Serializable;

/**
 * Implements a set using a TreeMap. [Sun
 * docs]
 *
 * @param  element type.
 */
public class TreeSet extends AbstractSet implements NavigableSet, Serializable {

  /**
   * TreeSet is stored as a TreeMap of the requested type to a constant Boolean.
   */
  private NavigableMap map;

  public TreeSet() {
    map = new TreeMap();
  }

  public TreeSet(Collection c) {
    this();
    addAll(c);
  }

  public TreeSet(Comparator c) {
    map = new TreeMap(c);
  }

  public TreeSet(SortedSet s) {
    this(checkNotNull(s).comparator());
    // TODO(jat): more efficient implementation
    addAll(s);
  }

  /**
   * Used to wrap subset maps in a new TreeSet.
   *
   * @param map map to use for backing store
   */
  private TreeSet(NavigableMap map) {
    this.map = map;
  }

  @Override
  public boolean add(E o) {
    // Use Boolean.FALSE as a convenient non-null value to store in the map
    return map.put(o, Boolean.FALSE) == null;
  }

  @Override
  public E ceiling(E e) {
    return map.ceilingKey(e);
  }

  @Override
  public void clear() {
    map.clear();
  }

  @Override
  public Comparator comparator() {
    return map.comparator();
  }

  @Override
  public boolean contains(Object o) {
    return map.containsKey(o);
  }

  @Override
  public Iterator descendingIterator() {
    return descendingSet().iterator();
  }

  @Override
  public NavigableSet descendingSet() {
    return new TreeSet(map.descendingMap());
  }

  @Override
  public E first() {
    return map.firstKey();
  }

  @Override
  public E floor(E e) {
    return map.floorKey(e);
  }

  @Override
  public SortedSet headSet(E toElement) {
    return headSet(toElement, false);
  }

  @Override
  public NavigableSet headSet(E toElement, boolean inclusive) {
    return new TreeSet(map.headMap(toElement, inclusive));
  }

  @Override
  public E higher(E e) {
    return map.higherKey(e);
  }

  @Override
  public Iterator iterator() {
    return map.keySet().iterator();
  }

  @Override
  public E last() {
    return map.lastKey();
  }

  @Override
  public E lower(E e) {
    return map.lowerKey(e);
  }

  @Override
  public E pollFirst() {
    return AbstractMap.getEntryKeyOrNull(map.pollFirstEntry());
  }

  @Override
  public E pollLast() {
    return AbstractMap.getEntryKeyOrNull(map.pollLastEntry());
  }

  @Override
  public boolean remove(Object o) {
    return map.remove(o) != null;
  }

  @Override
  public int size() {
    return map.size();
  }

  @Override
  public NavigableSet subSet(E fromElement, boolean fromInclusive,
      E toElement, boolean toInclusive) {
    return new TreeSet(map.subMap(fromElement, fromInclusive, toElement, toInclusive));
  }

  @Override
  public SortedSet subSet(E fromElement, E toElement) {
    return subSet(fromElement, true, toElement, false);
  }

  @Override
  public SortedSet tailSet(E fromElement) {
    return tailSet(fromElement, true);
  }

  @Override
  public NavigableSet tailSet(E fromElement, boolean inclusive) {
    return new TreeSet(map.tailMap(fromElement, inclusive));
  }
}