Java tutorial
/* * 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 {@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. */ 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<>()); } /** * 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 * {@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 {@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 {@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. */ 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<?> 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} * @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 */ @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 {@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 @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 <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; }