Java容器类源码学习-TreeSet（七）

一、官方介绍

基于TreeMap的NavigableSet实现。元素使用它们的自然顺序排序，或者通过在设置创建时提供的比较器进行排序，这取决于使用的是哪个构造函数。这个实现为基本操作(添加、删除和包含)提供了保证的log(n)时间开销。请注意，如果要正确实现set接口，set维护的顺序(不管是否提供显式comparator)必须与equals一致。(参见Comparable或Comparator获得与equals一致的精确定义。)这是因为Set接口是根据equals操作定义的，但是TreeSet实例使用它的compareTo(或compare)方法执行所有的元素比较，根据该方法判断两个元素是否相等。从Set的角度来看，equal。一个Set的行为是定义良好的，即使它的顺序与equals不一致;只是没有遵守Set接口的一般约定。(此段翻译很有争议，恳请指正)注意，这个实现不是同步的。如果多个线程同时访问tree set，并且至少有一个线程修改tree set，则必须在外部对tree set进行同步。这通常是通过对一些自然封装了集合的对象进行同步来实现的。如果不存在这样的对象，则应该使用集合来“包装”集合。Collections.synchronizedSortedSet方法。这最好在创建时完成，以防止意外的不同步访问Set: SortedSet s = Collections.synchronizedSortedSet(new TreeSet(...)); 这个类的iterator和listIterator方法返回的迭代器是 fail-fast的:如果在创建迭代器之后的任何时候，以任何方式(除了通过迭代器自己的删除或添加方法)对列表进行结构修改，迭代器将抛出ConcurrentModificationException异常。因此，在面对并发修改时，迭代器会快速而干净地失败，而不是在将来某个不确定的时间冒任意的、不确定的行为的风险。注意，不能保证迭代器的快速故障行为，因为通常来说，在存在非同步并发修改的情况下，不可能做出任何严格的保证。Fail-fast迭代器在最大努力的基础上抛出ConcurrentModificationException。因此，编写一个依赖于这个异常的正确性的程序是错误的:迭代器的 fail-fast 行为应该只用于检测bug。该类是Java集合框架的成员

二、源码分析

大部分方法都是对TreeMap的方法的封装，详细分析还是放在treeMap吧

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; } /** * 构造一个新的nullTreeMap，根据其元素的自然顺序排序。所有插入到集合中的元素必须实现可比接口。此外,所有这些元素都必须相互可比 */ public TreeSet() { this(new TreeMap<E, Object>()); } /** * 构造一个新的nullTreeMap，根据指定的比较器排序。所有元素插入到集合必须由指定比较器相互可比 * * @param comparator */ public TreeSet(Comparator<? super E> comparator) { this(new TreeMap<>(comparator)); } /** * 构造一个新的nullTreeMap，根据其元素的自然顺序排序。所有插入到集合中的元素必须实现可比接口。此外,所有这些元素都必须相互可比 * * @param c */ public TreeSet(Collection<? extends E> c) { this(); addAll(c); } /** * 构造一个包含相同元素的TreeMap，并使用与指定的已排序集相同的顺序。 * * @param s */ public TreeSet(SortedSet<E> s) { this(s.comparator()); addAll(s); } /** * 以升序返回此集合中元素的迭代器. * * @return an iterator over the elements in this set in ascending order */ public Iterator<E> iterator() { return m.navigableKeySet().iterator(); } /** * 按降序返回该集合中元素的迭代器。 * * @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(); } public boolean contains(Object o) { return m.containsKey(o); } public boolean add(E e) { return m.put(e, PRESENT) == null; } public boolean remove(Object o) { return m.remove(o) == PRESENT; } public void clear() { m.clear(); } public boolean addAll(Collection<? extends E> c) { // 如果符合，使用线性时间版本 具体介绍见TreeMap 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; }