从源码理解TreeMap.java

从源码理解TreeMap.java

package java.util;import java.io.Serializable;import java.util.function.BiConsumer;import java.util.function.BiFunction;import java.util.function.Consumer;/** * 基于红黑树的NavigableMap接口实现 * Map是根据关键字的自然比较序排序，或是根据创建时初始化的比较器的比较结果排序 * 这个实现保证提供log(n)时间的操作：containsKey、get、put、remove * 树形Map的顺序是保持不变的，和其他有序Map一样，不管有没有提供显式的比较器，而且必须和equals兼容 *  注意，这个实现是不支持并发访问的。需要外部显式同步，如下： *SortedMap m = Collections.synchronizedSortedMap(new TreeMap(...)); * 所有集合视图返回的迭代器都是快速失败的（fail-fast） */public class TreeMap<K,V>    extends AbstractMap<K,V>    implements NavigableMap<K,V>, Cloneable, java.io.Serializable{    /**     * 用于保持顺序的比较器，如果为空，使用自然序保持Key的顺序     */    private final Comparator<? super K> comparator;    //根节点    private transient Entry<K,V> root = null;    /**     * 树中的结点数量     */    private transient int size = 0;    /**     * 用于记录结构上的改变次数     */    private transient int modCount = 0;    /**     * 构造方法一，默认构造方法，Comparator为空，即采用自然序维持TreeMap中结点的顺序     */    public TreeMap() {        comparator = null;    }    /**     * 构造方法二，提供指定的比较器，如果为空，还是自然序     */    public TreeMap(Comparator<? super K> comparator) {        this.comparator = comparator;    }    /**     * 构造方法三，采用自然序维持TreeMap中结点的顺序，同时将传入的Map中的内容添加到TreeMap中     */    public TreeMap(Map<? extends K, ? extends V> m) {        comparator = null;        putAll(m);    }    /**     * 构造方法四，接受SortedMap参数，根据SortedMap的比较器维持TreeMap中的结点顺序，     * 同时通过buildFromSorted(int size, Iterator it,      * java.io.ObjectInputStream str, V defaultVal)方法将SortedMap中的 内容添加到TreeMap中     */    public TreeMap(SortedMap<K, ? extends V> m) {        comparator = m.comparator();        try {            buildFromSorted(m.size(), m.entrySet().iterator(), null, null);        } catch (java.io.IOException cannotHappen) {        } catch (ClassNotFoundException cannotHappen) {        }    }    // 查询操作    /**     * 返回Map中键值对数目     */    public int size() {        return size;    }    /**     * 是否包含指定关键字     */    public boolean containsKey(Object key) {        return getEntry(key) != null;    }    /**     * 是否包含指定值，时间复杂度和Map大小成正比     */    public boolean containsValue(Object value) {    //通过e = successor(e)实现对树的遍历        for (Entry<K,V> e = getFirstEntry(); e != null; e = successor(e))        //判断结点值是否和value相等            if (valEquals(value, e.value))                return true;               //若没有，返回false        return false;    }    /**     * 返回指定关键字的值，没有则返回null     * 返回null不代表不存在，也有可能是值就是null     * @throws ClassCastException if the specified key cannot be compared     *         with the keys currently in the map     * @throws NullPointerException if the specified key is null     *         and this map uses natural ordering, or its comparator     *         does not permit null keys     */    public V get(Object key) {        Entry<K,V> p = getEntry(key);        return (p==null ? null : p.value);    }    public Comparator<? super K> comparator() {        return comparator;    }    /**     * @throws NoSuchElementException {@inheritDoc}     */    public K firstKey() {        return key(getFirstEntry());    }    /**     * @throws NoSuchElementException {@inheritDoc}     */    public K lastKey() {        return key(getLastEntry());    }    /**     * 将指定Map中的映射复制进来，会取代当前已存在的映射值     * @param  map mappings to be stored in this map     * @throws ClassCastException if the class of a key or value in     *         the specified map prevents it from being stored in this map     * @throws NullPointerException if the specified map is null or     *         the specified map contains a null key and this map does not     *         permit null keys     */    public void putAll(Map<? extends K, ? extends V> map) {        int mapSize = map.size();        if (size==0 && mapSize!=0 && map instanceof SortedMap) {            Comparator<?> c = ((SortedMap<?,?>)map).comparator();            if (c == comparator || (c != null && c.equals(comparator))) {                ++modCount;                try {                    buildFromSorted(mapSize, map.entrySet().iterator(),                                    null, null);                } catch (java.io.IOException cannotHappen) {                } catch (ClassNotFoundException cannotHappen) {                }                return;            }        }        super.putAll(map);    }    /**     * 通过Key获取对应的结点     * @return this map's entry for the given key, or {@code null} if the map     *         does not contain an entry for the key     * @throws ClassCastException if the specified key cannot be compared     *         with the keys currently in the map     * @throws NullPointerException if the specified key is null     *         and this map uses natural ordering, or its comparator     *         does not permit null keys     */    final Entry<K,V> getEntry(Object key) {        // 如果有比较器，返回getEntryUsingComparator(Object key)的结果        if (comparator != null)            return getEntryUsingComparator(key);        //查找的Key为null，抛出NullPointerException        if (key == null)            throw new NullPointerException();        @SuppressWarnings("unchecked")        //如果没有比较器，而是实现了 可比较接口            Comparable<? super K> k = (Comparable<? super K>) key;        //获取根节点        Entry<K,V> p = root;        //对树进行遍历查找结点        while (p != null) {        //把Key和当前节点的Key进行比较            int cmp = k.compareTo(p.key);            //Key小于当前结点的Key            if (cmp < 0)            //p“移动”到左节点上                p = p.left;            //key大于当前节点的Key            else if (cmp > 0)            //p移动到右结点上                p = p.right;            //key值相等则当前节点就是要找的结点            else            //返回找到的结点                return p;        }        //没有找到则返回null        return null;    }    /**     * 有比较器时获取指定关键字的Entry的方法     */    final Entry<K,V> getEntryUsingComparator(Object key) {        @SuppressWarnings("unchecked")            K k = (K) key;        //获取比较器        Comparator<? super K> cpr = comparator;        //其实在调用此方法的get(Object key)中已经对比较器为null的情况进行判断，这里是防御性的判断        if (cpr != null) {        //获取根节点            Entry<K,V> p = root;            //遍历树            while (p != null) {            //获取Key和当前节点的Key的比较结果                int cmp = cpr.compare(k, p.key);                //查找的Key值较小                if (cmp < 0)                //p移动到左孩子                    p = p.left;                //查找的Key值较大                else if (cmp > 0)                //p移动到右结点                    p = p.right;                //key值相等                else                //返回找到的结点                    return p;            }        }        //没找到Key值对应的结点，返回null        return null;    }    /**     * 获取指定关键字对应的Entry，如果没有就返回大于该关键字的最小关键字的Entry     * 如没有，返回null     */    final Entry<K,V> getCeilingEntry(K key) {        Entry<K,V> p = root;        while (p != null) {            int cmp = compare(key, p.key);            //key比较小            if (cmp < 0) {            //进入左子树遍历                if (p.left != null)                    p = p.left;                else                    return p;            } else if (cmp > 0) {//key比较大            //进入右子树遍历                if (p.right != null) {                    p = p.right;                } else {//如果没有右子树，向上返回直到根节点或是走到一个左孩子结点                    Entry<K,V> parent = p.parent;                    Entry<K,V> ch = p;                    while (parent != null && ch == parent.right) {                        ch = parent;                        parent = parent.parent;                    }                    return parent;                }            } else                return p;        }        return null;    }    /**     * 获取指定关键字对应的Entry，如果没有对应的Entry，返回小于等于指定关键字的最大关键字的Entry，     * 如果不存在，返回null     */    final Entry<K,V> getFloorEntry(K key) {    //获取根节点        Entry<K,V> p = root;        //不是空树，对树进行遍历        while (p != null) {            int cmp = compare(key, p.key);            //key较大            if (cmp > 0) {            //找到结点有右孩子，则继续向右孩子遍历                if (p.right != null)                    p = p.right;                else//没有右孩子，那么p结点就是树中比传入key值小且最接近传入key的结点，就是要找的结点                    return p;            } else if (cmp < 0) {//key值较小            //由左孩子向左孩子遍历                if (p.left != null) {                     p = p.left;                } else {//没有左孩子，这个结点比key值大，                //返回内容是向上寻找到的根节点或比传入key值小的最后一个结点                    Entry<K,V> parent = p.parent;                    Entry<K,V> ch = p;                    while (parent != null && ch == parent.left) {                        ch = parent;                        parent = parent.parent;                    }                    return parent;                }            } else//Key值相等                return p;        }        return null;    }    /**     * 获取指定关键字对应的Entry，如果没有对应的Entry，返回严格大于指定关键字的最小关键字的Entry，     * 如果没有则返回null     */    final Entry<K,V> getHigherEntry(K key) {    //获取根节点        Entry<K,V> p = root;        //树不空，遍历树        while (p != null) {            int cmp = compare(key, p.key);            //key比较小            if (cmp < 0) {            //有左孩子，去左子树遍历                if (p.left != null)                    p = p.left;                else//没有左孩子，那么p结点就是树中比传入key值大且最接近传入key的结点了                    return p;            } else { //key比较大            //有右子树，向右子树遍历                if (p.right != null) {                    p = p.right;                } else {//没有右孩子，这个结点比key小，                //返回内容是向上寻找到根节点或是比传入key值大的最后一个结点                    Entry<K,V> parent = p.parent;                    Entry<K,V> ch = p;                    while (parent != null && ch == parent.right) {                        ch = parent;                        parent = parent.parent;                    }                    return parent;                }            }        }        return null;    }    /**     * 返回严格小于指定关键字的的最大关键字的Entry     */    final Entry<K,V> getLowerEntry(K key) {        Entry<K,V> p = root;        while (p != null) {            int cmp = compare(key, p.key);            if (cmp > 0) {                if (p.right != null)                    p = p.right;                else                    return p;            } else {                if (p.left != null) {                    p = p.left;                } else {                    Entry<K,V> parent = p.parent;                    Entry<K,V> ch = p;                    while (parent != null && ch == parent.left) {                        ch = parent;                        parent = parent.parent;                    }                    return parent;                }            }        }        return null;    }    /**将指定关键字和指定值联系起来，如已存在，覆盖     * @param key key with which the specified value is to be associated     * @param value value to be associated with the specified key     *     * @return the previous value associated with {@code key}, or     *         {@code null} if there was no mapping for {@code key}.     *         (A {@code null} return can also indicate that the map     *         previously associated {@code null} with {@code key}.)     * @throws ClassCastException if the specified key cannot be compared     *         with the keys currently in the map     * @throws NullPointerException if the specified key is null     *         and this map uses natural ordering, or its comparator     *         does not permit null keys     */    public V put(K key, V value) {        Entry<K,V> t = root;        if (t == null) {            compare(key, key); // 类型检查（可能为null）            //如果根节点为null，将传入的键值对构造成根节点（根节点没有父节点，所以传入的父节点为null）            root = new Entry<>(key, value, null);            size = 1;            modCount++;            return null;        }        //记录比较结果        int cmp;        Entry<K,V> parent;        // 分割比较器和可比较接口的处理        Comparator<? super K> cpr = comparator;        //有比较器的处理        if (cpr != null) {        //do while实现从根节点root开始移动寻找传入键值对需要插入的位置            do {            //记录将要被插入新的键值对的上一个结点（即新节点的父节点）                parent = t;                //使用比较器比较父节点和插入键值对的Key值的大小                cmp = cpr.compare(key, t.key);                //插入的Key较大，进入左子树                if (cmp < 0)                    t = t.left;                //插入的Key较小，进入右子树                else if (cmp > 0)                    t = t.right;                //key值相等，替换并返回t结点的value（put方法结束）                else                    return t.setValue(value);            } while (t != null);        }        //没有比较器的处理        else {        //Key为null，抛出NullPointerException异常            if (key == null)                throw new NullPointerException();            @SuppressWarnings("unchecked")                Comparable<? super K> k = (Comparable<? super K>) key;            //与if中的do while类似，只是比较的方式不同            do {                parent = t;                cmp = k.compareTo(t.key);                if (cmp < 0)                    t = t.left;                else if (cmp > 0)                    t = t.right;                else                    return t.setValue(value);            } while (t != null);        }        //没有找到Key相同的结点才会有下面的操作        //根据传入的键值对和找到的“父节点”创建新节点        Entry<K,V> e = new Entry<>(key, value, parent);        //根据最后一次的判断结果确认新节点是“父节点”的左孩子还是右孩子        if (cmp < 0)            parent.left = e;        else            parent.right = e;        //对加入新节点的树进行调整        fixAfterInsertion(e);        //记录Size和modCount        size++;        modCount++;        //因为是插入新节点，所以返回是null        return null;    }    /**     * 删除指定关键字的映射     * @param  key key for which mapping should be removed     * @return the previous value associated with {@code key}, or     *         {@code null} if there was no mapping for {@code key}.     *         (A {@code null} return can also indicate that the map     *         previously associated {@code null} with {@code key}.)     * @throws ClassCastException if the specified key cannot be compared     *         with the keys currently in the map     * @throws NullPointerException if the specified key is null     *         and this map uses natural ordering, or its comparator     *         does not permit null keys     */    public V remove(Object key) {    //通过getEntry(Object key)获取结点        Entry<K,V> p = getEntry(key);        //指定Key的结点不存在，返回null        if (p == null)            return null;        //获取结点的value        V oldValue = p.value;        //删除结点        deleteEntry(p);        //返回结点的值        return oldValue;    }    /**     * 清空Map     */    public void clear() {        modCount++;        size = 0;        root = null;    }    /**     * Returns a shallow copy of this {@code TreeMap} instance. (The keys and     * values themselves are not cloned.)     *     * @return a shallow copy of this map     */    public Object clone() {        TreeMap<?,?> clone;        try {            clone = (TreeMap<?,?>) super.clone();        } catch (CloneNotSupportedException e) {            throw new InternalError(e);        }        // Put clone into "virgin" state (except for comparator)        clone.root = null;        clone.size = 0;        clone.modCount = 0;        clone.entrySet = null;        clone.navigableKeySet = null;        clone.descendingMap = null;        // Initialize clone with our mappings        try {            clone.buildFromSorted(size, entrySet().iterator(), null, null);        } catch (java.io.IOException cannotHappen) {        } catch (ClassNotFoundException cannotHappen) {        }        return clone;    }    // NavigableMap接口的函数    /**     * @since 1.6     */    public Map.Entry<K,V> firstEntry() {        return exportEntry(getFirstEntry());    }    /**     * @since 1.6     */    public Map.Entry<K,V> lastEntry() {        return exportEntry(getLastEntry());    }    /**     * 获取并移除最小结点     * @since 1.6     */    public Map.Entry<K,V> pollFirstEntry() {        Entry<K,V> p = getFirstEntry();        Map.Entry<K,V> result = exportEntry(p);        if (p != null)            deleteEntry(p);        return result;    }    /**     * 获取并移除最大结点     * @since 1.6     */    public Map.Entry<K,V> pollLastEntry() {        Entry<K,V> p = getLastEntry();        Map.Entry<K,V> result = exportEntry(p);        if (p != null)            deleteEntry(p);        return result;    }    /**     * @throws ClassCastException {@inheritDoc}     * @throws NullPointerException if the specified key is null     *         and this map uses natural ordering, or its comparator     *         does not permit null keys     * @since 1.6     */    public Map.Entry<K,V> lowerEntry(K key) {        return exportEntry(getLowerEntry(key));    }    /**     * @throws ClassCastException {@inheritDoc}     * @throws NullPointerException if the specified key is null     *         and this map uses natural ordering, or its comparator     *         does not permit null keys     * @since 1.6     */    public K lowerKey(K key) {        return keyOrNull(getLowerEntry(key));    }    /**     * @throws ClassCastException {@inheritDoc}     * @throws NullPointerException if the specified key is null     *         and this map uses natural ordering, or its comparator     *         does not permit null keys     * @since 1.6     */    public Map.Entry<K,V> floorEntry(K key) {        return exportEntry(getFloorEntry(key));    }    /**     * @throws ClassCastException {@inheritDoc}     * @throws NullPointerException if the specified key is null     *         and this map uses natural ordering, or its comparator     *         does not permit null keys     * @since 1.6     */    public K floorKey(K key) {        return keyOrNull(getFloorEntry(key));    }    /**     * @throws ClassCastException {@inheritDoc}     * @throws NullPointerException if the specified key is null     *         and this map uses natural ordering, or its comparator     *         does not permit null keys     * @since 1.6     */    public Map.Entry<K,V> ceilingEntry(K key) {        return exportEntry(getCeilingEntry(key));    }    /**     * @throws ClassCastException {@inheritDoc}     * @throws NullPointerException if the specified key is null     *         and this map uses natural ordering, or its comparator     *         does not permit null keys     * @since 1.6     */    public K ceilingKey(K key) {        return keyOrNull(getCeilingEntry(key));    }    /**     * @throws ClassCastException {@inheritDoc}     * @throws NullPointerException if the specified key is null     *         and this map uses natural ordering, or its comparator     *         does not permit null keys     * @since 1.6     */    public Map.Entry<K,V> higherEntry(K key) {        return exportEntry(getHigherEntry(key));    }    /**     * @throws ClassCastException {@inheritDoc}     * @throws NullPointerException if the specified key is null     *         and this map uses natural ordering, or its comparator     *         does not permit null keys     * @since 1.6     */    public K higherKey(K key) {        return keyOrNull(getHigherEntry(key));    }    // Views    /**     * Fields initialized to contain an instance of the entry set view     * the first time this view is requested.  Views are stateless, so     * there's no reason to create more than one.     */    private transient EntrySet entrySet = null;    private transient KeySet<K> navigableKeySet = null;    private transient NavigableMap<K,V> descendingMap = null;    /**     * Returns a {@link Set} view of the keys contained in this map.     *     * <p>The set's iterator returns the keys in ascending order.     * The set's spliterator is     * <em><a href="Spliterator.html#binding">late-binding</a></em>,     * <em>fail-fast</em>, and additionally reports {@link Spliterator#SORTED}     * and {@link Spliterator#ORDERED} with an encounter order that is ascending     * key order.  The spliterator's comparator (see     * {@link java.util.Spliterator#getComparator()}) is {@code null} if     * the tree map'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 map's comparator.     *     * <p>The set is backed by the map, so changes to the map are     * reflected in the set, and vice-versa.  If the map is modified     * while an iteration over the set is in progress (except through     * the iterator's own {@code remove} operation), the results of     * the iteration are undefined.  The set supports element removal,     * which removes the corresponding mapping from the map, via the     * {@code Iterator.remove}, {@code Set.remove},     * {@code removeAll}, {@code retainAll}, and {@code clear}     * operations.  It does not support the {@code add} or {@code addAll}     * operations.     */    public Set<K> keySet() {        return navigableKeySet();    }    public NavigableSet<K> navigableKeySet() {        KeySet<K> nks = navigableKeySet;        return (nks != null) ? nks : (navigableKeySet = new KeySet<>(this));    }    public NavigableSet<K> descendingKeySet() {        return descendingMap().navigableKeySet();    }    /**     * Returns a {@link Collection} view of the values contained in this map.     *     * <p>The collection's iterator returns the values in ascending order     * of the corresponding keys. The collection's spliterator is     * <em><a href="Spliterator.html#binding">late-binding</a></em>,     * <em>fail-fast</em>, and additionally reports {@link Spliterator#ORDERED}     * with an encounter order that is ascending order of the corresponding     * keys.     *     * <p>The collection is backed by the map, so changes to the map are     * reflected in the collection, and vice-versa.  If the map is     * modified while an iteration over the collection is in progress     * (except through the iterator's own {@code remove} operation),     * the results of the iteration are undefined.  The collection     * supports element removal, which removes the corresponding     * mapping from the map, via the {@code Iterator.remove},     * {@code Collection.remove}, {@code removeAll},     * {@code retainAll} and {@code clear} operations.  It does not     * support the {@code add} or {@code addAll} operations.     */    public Collection<V> values() {        Collection<V> vs = values;        return (vs != null) ? vs : (values = new Values());    }    /**     * Returns a {@link Set} view of the mappings contained in this map.     *     * <p>The set's iterator returns the entries in ascending key order. The     * sets's spliterator is     * <em><a href="Spliterator.html#binding">late-binding</a></em>,     * <em>fail-fast</em>, and additionally reports {@link Spliterator#SORTED} and     * {@link Spliterator#ORDERED} with an encounter order that is ascending key     * order.     *     * <p>The set is backed by the map, so changes to the map are     * reflected in the set, and vice-versa.  If the map is modified     * while an iteration over the set is in progress (except through     * the iterator's own {@code remove} operation, or through the     * {@code setValue} operation on a map entry returned by the     * iterator) the results of the iteration are undefined.  The set     * supports element removal, which removes the corresponding     * mapping from the map, via the {@code Iterator.remove},     * {@code Set.remove}, {@code removeAll}, {@code retainAll} and     * {@code clear} operations.  It does not support the     * {@code add} or {@code addAll} operations.     */    public Set<Map.Entry<K,V>> entrySet() {        EntrySet es = entrySet;        return (es != null) ? es : (entrySet = new EntrySet());    }    public NavigableMap<K, V> descendingMap() {        NavigableMap<K, V> km = descendingMap;        return (km != null) ? km :            (descendingMap = new DescendingSubMap<>(this,                                                    true, null, true,                                                    true, null, true));    }    /**     * @throws ClassCastException       {@inheritDoc}     * @throws NullPointerException if {@code fromKey} or {@code toKey} is     *         null and this map uses natural ordering, or its comparator     *         does not permit null keys     * @throws IllegalArgumentException {@inheritDoc}     * @since 1.6     */    public NavigableMap<K,V> subMap(K fromKey, boolean fromInclusive,                                    K toKey,   boolean toInclusive) {        return new AscendingSubMap<>(this,                                     false, fromKey, fromInclusive,                                     false, toKey,   toInclusive);    }    /**     * @throws ClassCastException       {@inheritDoc}     * @throws NullPointerException if {@code toKey} is null     *         and this map uses natural ordering, or its comparator     *         does not permit null keys     * @throws IllegalArgumentException {@inheritDoc}     * @since 1.6     */    public NavigableMap<K,V> headMap(K toKey, boolean inclusive) {        return new AscendingSubMap<>(this,                                     true,  null,  true,                                     false, toKey, inclusive);    }    /**     * @throws ClassCastException       {@inheritDoc}     * @throws NullPointerException if {@code fromKey} is null     *         and this map uses natural ordering, or its comparator     *         does not permit null keys     * @throws IllegalArgumentException {@inheritDoc}     * @since 1.6     */    public NavigableMap<K,V> tailMap(K fromKey, boolean inclusive) {        return new AscendingSubMap<>(this,                                     false, fromKey, inclusive,                                     true,  null,    true);    }    /**     * @throws ClassCastException       {@inheritDoc}     * @throws NullPointerException if {@code fromKey} or {@code toKey} is     *         null and this map uses natural ordering, or its comparator     *         does not permit null keys     * @throws IllegalArgumentException {@inheritDoc}     */    public SortedMap<K,V> subMap(K fromKey, K toKey) {        return subMap(fromKey, true, toKey, false);    }    /**     * @throws ClassCastException       {@inheritDoc}     * @throws NullPointerException if {@code toKey} is null     *         and this map uses natural ordering, or its comparator     *         does not permit null keys     * @throws IllegalArgumentException {@inheritDoc}     */    public SortedMap<K,V> headMap(K toKey) {        return headMap(toKey, false);    }    /**     * @throws ClassCastException       {@inheritDoc}     * @throws NullPointerException if {@code fromKey} is null     *         and this map uses natural ordering, or its comparator     *         does not permit null keys     * @throws IllegalArgumentException {@inheritDoc}     */    public SortedMap<K,V> tailMap(K fromKey) {        return tailMap(fromKey, true);    }    @Override    public boolean replace(K key, V oldValue, V newValue) {        Entry<K,V> p = getEntry(key);        if (p!=null && Objects.equals(oldValue, p.value)) {            p.value = newValue;            return true;        }        return false;    }    @Override    public V replace(K key, V value) {        Entry<K,V> p = getEntry(key);        if (p!=null) {            V oldValue = p.value;            p.value = value;            return oldValue;        }        return null;    }    @Override    public void forEach(BiConsumer<? super K, ? super V> action) {        Objects.requireNonNull(action);        int expectedModCount = modCount;        for (Entry<K, V> e = getFirstEntry(); e != null; e = successor(e)) {            action.accept(e.key, e.value);            if (expectedModCount != modCount) {                throw new ConcurrentModificationException();            }        }    }    @Override    public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {        Objects.requireNonNull(function);        int expectedModCount = modCount;        for (Entry<K, V> e = getFirstEntry(); e != null; e = successor(e)) {            e.value = function.apply(e.key, e.value);            if (expectedModCount != modCount) {                throw new ConcurrentModificationException();            }        }    }    // 视图类支持    //集合类Values    class Values extends AbstractCollection<V> {    //提供集合类Values的迭代器        public Iterator<V> iterator() {            return new ValueIterator(getFirstEntry());        }        //返回TreeMap中保存的结点数        public int size() {            return TreeMap.this.size();        }        //判断TreeMap中是否存在Value为o的结点        public boolean contains(Object o) {            return TreeMap.this.containsValue(o);        }        //删除一个对象        public boolean remove(Object o) {        //遍历TreeMap            for (Entry<K,V> e = getFirstEntry(); e != null; e = successor(e)) {            //寻找值相等的结点                if (valEquals(e.getValue(), o)) {                //删除找到的结点                    deleteEntry(e);                    return true;                }            }            return false;        }        //清空TreeMap        public void clear() {            TreeMap.this.clear();        }        public Spliterator<V> spliterator() {            return new ValueSpliterator<K,V>(TreeMap.this, null, null, 0, -1, 0);        }    }    class EntrySet extends AbstractSet<Map.Entry<K,V>> {    //iterator()方法返回的是EntryIterator对象        public Iterator<Map.Entry<K,V>> iterator() {            return new EntryIterator(getFirstEntry());        }        //判断是否包含某个结点的方法        public boolean contains(Object o) {            if (!(o instanceof Map.Entry))                return false;            Map.Entry<?,?> entry = (Map.Entry<?,?>) o;            Object value = entry.getValue();            Entry<K,V> p = getEntry(entry.getKey());            //判断是否包含某个对象的标准是存在结点的key与传入对象的key值相同，            //且该结点的value也与传入对象的value值相等            return p != null && valEquals(p.getValue(), value);        }        //删除一个对象        public boolean remove(Object o) {            if (!(o instanceof Map.Entry))                return false;            Map.Entry<?,?> entry = (Map.Entry<?,?>) o;            Object value = entry.getValue();            Entry<K,V> p = getEntry(entry.getKey());            //如果存在该对象，则进行删除操作并返回true            if (p != null && valEquals(p.getValue(), value)) {                deleteEntry(p);                return true;            }            //不存在直接返回false            return false;        }        //size()返回的是TreeMap中包含的结点的数量        public int size() {            return TreeMap.this.size();        }        //clear()方法实际调用了TreeMap的clear()方法，与size()方法都是代理方法        public void clear() {            TreeMap.this.clear();        }        public Spliterator<Map.Entry<K,V>> spliterator() {            return new EntrySpliterator<K,V>(TreeMap.this, null, null, 0, -1, 0);        }    }    /*     * 与Values和EntrySet不同，KeySet类是静态的，     * KeySet实现了NavigableSet接口，意思是可导航的Set，包含更多的获取指定结点的方法     */    Iterator<K> keyIterator() {        return new KeyIterator(getFirstEntry());    }    Iterator<K> descendingKeyIterator() {        return new DescendingKeyIterator(getLastEntry());    }    static final class KeySet<E> extends AbstractSet<E> implements NavigableSet<E> {        private final NavigableMap<E, ?> m;        //构造方法        KeySet(NavigableMap<E,?> map) { m = map; }        public Iterator<E> iterator() {            if (m instanceof TreeMap)                return ((TreeMap<E,?>)m).keyIterator();            else                return ((TreeMap.NavigableSubMap<E,?>)m).keyIterator();        }        public Iterator<E> descendingIterator() {            if (m instanceof TreeMap)                return ((TreeMap<E,?>)m).descendingKeyIterator();            else                return ((TreeMap.NavigableSubMap<E,?>)m).descendingKeyIterator();        }        //size()方法返回的是通过构造方法传入的Map的大小        public int size() { return m.size(); }        //判断传入的Map是否为空        public boolean isEmpty() { return m.isEmpty(); }        //判断传入的Map中是否包含这个Key        public boolean contains(Object o) { return m.containsKey(o); }        public void clear() { m.clear(); }        //因为传入的Map是NavigableMap，所以下面这几个方法都是代理方法，调用Map中相应的方法        public E lower(E e) { return m.lowerKey(e); }        public E floor(E e) { return m.floorKey(e); }        public E ceiling(E e) { return m.ceilingKey(e); }        public E higher(E e) { return m.higherKey(e); }        public E first() { return m.firstKey(); }        public E last() { return m.lastKey(); }        //获取传入Map的比较器        public Comparator<? super E> comparator() { return m.comparator(); }        //获取Map中第一个结点的key        public E pollFirst() {            Map.Entry<E,?> e = m.pollFirstEntry();            return (e == null) ? null : e.getKey();        }        //获取Map中最后一个结点的key        public E pollLast() {            Map.Entry<E,?> e = m.pollLastEntry();            return (e == null) ? null : e.getKey();        }        //删除一个对象，实际上是删除Map中以这个对象为key的一个结点        public boolean remove(Object o) {            int oldSize = size();            m.remove(o);            return size() != oldSize;        }        public NavigableSet<E> subSet(E fromElement, boolean fromInclusive,                                      E toElement,   boolean toInclusive) {            return new KeySet<>(m.subMap(fromElement, fromInclusive,                                          toElement,   toInclusive));        }        public NavigableSet<E> headSet(E toElement, boolean inclusive) {            return new KeySet<>(m.headMap(toElement, inclusive));        }        public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {            return new KeySet<>(m.tailMap(fromElement, inclusive));        }        public SortedSet<E> subSet(E fromElement, E toElement) {            return subSet(fromElement, true, toElement, false);        }        public SortedSet<E> headSet(E toElement) {            return headSet(toElement, false);        }        public SortedSet<E> tailSet(E fromElement) {            return tailSet(fromElement, true);        }        public NavigableSet<E> descendingSet() {            return new KeySet<>(m.descendingMap());        }        public Spliterator<E> spliterator() {            return keySpliteratorFor(m);        }    }    /**     * TreeMap 迭代器相关的内部类     */    abstract class PrivateEntryIterator<T> implements Iterator<T> {    //指向next的引用        Entry<K,V> next;        //保留对上一次返回结点的引用        Entry<K,V> lastReturned;        int expectedModCount;        //构造方法，lastReturned置空，next指向传入的结点        PrivateEntryIterator(Entry<K,V> first) {            expectedModCount = modCount;            lastReturned = null;            next = first;        }        //判断是否还有下一个结点        public final boolean hasNext() {            return next != null;        }        //返回下一个结点        final Entry<K,V> nextEntry() {            Entry<K,V> e = next;            if (e == null)                throw new NoSuchElementException();            if (modCount != expectedModCount)                throw new ConcurrentModificationException();            //next移动它的后继            next = successor(e);            //记录被返回的结点            lastReturned = e;            //返回原先记录的next结点            return e;        }        //返回前一个结点        final Entry<K,V> prevEntry() {            Entry<K,V> e = next;            if (e == null)                throw new NoSuchElementException();            if (modCount != expectedModCount)                throw new ConcurrentModificationException();            //获取指定结点的前一个结点（按遍历次序的前一个结点）            next = predecessor(e);            //记录被返回的结点            lastReturned = e;            return e;        }        //移除最近一次被返回的结点        public void remove() {            if (lastReturned == null)                throw new IllegalStateException();            if (modCount != expectedModCount)                throw new ConcurrentModificationException();            // deleted entries are replaced by their successors            if (lastReturned.left != null && lastReturned.right != null)            //如果被删除结点有两个孩子，删除结点e的时候e的引用会被修改为指向原结点的继承者，            //所以这里先保留next对lastReturned的引用，这样在删除结点后就能获取到继承者的引用，继而继续遍历树                next = lastReturned;            //删除结点            deleteEntry(lastReturned);            expectedModCount = modCount;            lastReturned = null;        }    }    final class EntryIterator extends PrivateEntryIterator<Map.Entry<K,V>> {        EntryIterator(Entry<K,V> first) {            super(first);        }        public Map.Entry<K,V> next() {            return nextEntry();        }    }    //value的迭代器    final class ValueIterator extends PrivateEntryIterator<V> {        ValueIterator(Entry<K,V> first) {            super(first);        }        //next()方法返回的是结点的value值        public V next() {            return nextEntry().value;        }    }    //key迭代器    final class KeyIterator extends PrivateEntryIterator<K> {        KeyIterator(Entry<K,V> first) {            super(first);        }        //next()方法返回的是结点的key        public K next() {            return nextEntry().key;        }    }    //逆序的key迭代器    final class DescendingKeyIterator extends PrivateEntryIterator<K> {        DescendingKeyIterator(Entry<K,V> first) {            super(first);        }        //next()方法返回的是结点的前一个结点（按遍历次序的前一个结点）的key        public K next() {            return prevEntry().key;        }        public void remove() {            if (lastReturned == null)                throw new IllegalStateException();            if (modCount != expectedModCount)                throw new ConcurrentModificationException();            deleteEntry(lastReturned);            lastReturned = null;            expectedModCount = modCount;        }    }    // 工具函数    /**     * Compares two keys using the correct comparison method for this TreeMap.     */    @SuppressWarnings("unchecked")    final int compare(Object k1, Object k2) {        return comparator==null ? ((Comparable<? super K>)k1).compareTo((K)k2)            : comparator.compare((K)k1, (K)k2);    }    /**     * Test two values for equality.  Differs from o1.equals(o2) only in     * that it copes with {@code null} o1 properly.     */    static final boolean valEquals(Object o1, Object o2) {        return (o1==null ? o2==null : o1.equals(o2));    }    /**     * Return SimpleImmutableEntry for entry, or null if null     */    static <K,V> Map.Entry<K,V> exportEntry(TreeMap.Entry<K,V> e) {        return (e == null) ? null :            new AbstractMap.SimpleImmutableEntry<>(e);    }    /**     * Return key for entry, or null if null     */    static <K,V> K keyOrNull(TreeMap.Entry<K,V> e) {        return (e == null) ? null : e.key;    }    /**     * Returns the key corresponding to the specified Entry.     * @throws NoSuchElementException if the Entry is null     */    static <K> K key(Entry<K,?> e) {        if (e==null)            throw new NoSuchElementException();        return e.key;    }    // SubMaps    /**     * Dummy value serving as unmatchable fence key for unbounded     * SubMapIterators     */    private static final Object UNBOUNDED = new Object();    /**     * @serial include     */    abstract static class NavigableSubMap<K,V> extends AbstractMap<K,V>        implements NavigableMap<K,V>, java.io.Serializable {        private static final long serialVersionUID = -2102997345730753016L;        /**         * 存储内容的Map.         */        final TreeMap<K,V> m;        /**         * 端点被表示为两个三元组(fromStart, lo,loInclusive)和(toEnd, hi, hiInclusive).          * 如果fromStart为真，下界lo无效，从Map中的第一个结点开始，如果loInclusive为真，下界包含lo         * 上界类似         */        final K lo, hi;//lowKey、highKey        final boolean fromStart, toEnd;//标识Map的边界是否是Map的第一个结点和最后一个结点        final boolean loInclusive, hiInclusive;//是否包含最低lo、最高位置hi        //通过上面的三组变量可以组成两个三元组表示一个集合的两个端点        //构造方法        NavigableSubMap(TreeMap<K,V> m,                        boolean fromStart, K lo, boolean loInclusive,                        boolean toEnd,     K hi, boolean hiInclusive) {            if (!fromStart && !toEnd) {            //lo>hi抛出异常                if (m.compare(lo, hi) > 0)                    throw new IllegalArgumentException("fromKey > toKey");            } else {                if (!fromStart) // type check                    m.compare(lo, lo);                if (!toEnd)                    m.compare(hi, hi);            }            this.m = m;            this.fromStart = fromStart;            this.lo = lo;            this.loInclusive = loInclusive;            this.toEnd = toEnd;            this.hi = hi;            this.hiInclusive = hiInclusive;        }        // 内部工具函数        //tooLow判断传入的key是否太小        final boolean tooLow(Object key) {        //如果fromStart为false，需要判断最低边界            if (!fromStart) {                int c = m.compare(key, lo);                //如果key<lo或者（相等但是Map的边界不包含lo），那么key越界了，即小于最小值                if (c < 0 || (c == 0 && !loInclusive))                    return true;            }            //默认返回false            return false;        }        //判断传入的key是否太大        final boolean tooHigh(Object key) {            if (!toEnd) {                int c = m.compare(key, hi);                if (c > 0 || (c == 0 && !hiInclusive))                    return true;            }            return false;        }        //判断是否在范围内，即满足最低最高限制，结合tooLow和tooHigh即可        final boolean inRange(Object key) {            return !tooLow(key) && !tooHigh(key);        }        //是否在封闭的区间内        final boolean inClosedRange(Object key) {            return (fromStart || m.compare(key, lo) >= 0)                && (toEnd || m.compare(hi, key) >= 0);        }        //判断是否在一个区间内        final boolean inRange(Object key, boolean inclusive) {            return inclusive ? inRange(key) : inClosedRange(key);        }        /*         * Absolute versions of relation operations.         * Subclasses map to these using like-named "sub"         * versions that invert senses for descending maps         */        //获取绝对的最低结点        final TreeMap.Entry<K,V> absLowest() {        //如果fromStart为true，第一个结点就是最低结点，获取第一个结点        //否则根据loInclusive是否为true，即是否包含lo来决定获取Ceiling结点或Higher结点        //getCeilingEntry意为获取指定key的结点或者比指定key大的最小结点，不存在则返回null        //getHigherEntry意为获取比指定key大的最小结点，不存在则返回null            TreeMap.Entry<K,V> e =                (fromStart ?  m.getFirstEntry() :                 (loInclusive ? m.getCeilingEntry(lo) :                                m.getHigherEntry(lo)));            return (e == null || tooHigh(e.key)) ? null : e;        }        //获取绝对的最大结点        final TreeMap.Entry<K,V> absHighest() {            TreeMap.Entry<K,V> e =                (toEnd ?  m.getLastEntry() :                 (hiInclusive ?  m.getFloorEntry(hi) :                                 m.getLowerEntry(hi)));            return (e == null || tooLow(e.key)) ? null : e;        }        //寻找大于等于key的最小结点        final TreeMap.Entry<K,V> absCeiling(K key) {        //如果key太小，返回绝对的最小的结点            if (tooLow(key))                return absLowest();            //获取允许的key的极限结点（满足要求的最小的结点）            TreeMap.Entry<K,V> e = m.getCeilingEntry(key);            return (e == null || tooHigh(e.key)) ? null : e;        }        //和absCeiling类似，只是获取的不包含相等的情况，而是寻找大于key的最小结点         final TreeMap.Entry<K,V> absHigher(K key) {            if (tooLow(key))                return absLowest();            TreeMap.Entry<K,V> e = m.getHigherEntry(key);            return (e == null || tooHigh(e.key)) ? null : e;        }        //获取绝对的小于等于key的结点        final TreeMap.Entry<K,V> absFloor(K key) {        //指定的key超出了hi，直接返回绝对的允许的最大的结点            if (tooHigh(key))                return absHighest();            //getFloorEntry获取的是指定key的结点，            //如果不存在这样的结点，就去获取比指定key小的最大结点，            //如果仍然不存在，返回null            TreeMap.Entry<K,V> e = m.getFloorEntry(key);            return (e == null || tooLow(e.key)) ? null : e;        }        //与absFloor类似，只是不包含等于的情况        final TreeMap.Entry<K,V> absLower(K key) {            if (tooHigh(key))                return absHighest();            TreeMap.Entry<K,V> e = m.getLowerEntry(key);            return (e == null || tooLow(e.key)) ? null : e;        }        /** 返回比最大结点还要大的结点（Fence是栅栏、围栏的意思） */        final TreeMap.Entry<K,V> absHighFence() {        //如果toEnd是true，即上界是Map中的最大结点，那么围在它外面的是null，        //如果是false，根据hi是否被包含返回getHigherEntry或getCeilingEntry            return (toEnd ? null : (hiInclusive ?                                    m.getHigherEntry(hi) :                                    m.getCeilingEntry(hi)));        }        /** 为降序遍历返回比最小结点还要小的结点 */        final TreeMap.Entry<K,V> absLowFence() {            return (fromStart ? null : (loInclusive ?                                        m.getLowerEntry(lo) :                                        m.getFloorEntry(lo)));        }        // Abstract methods defined in ascending vs descending classes        // These relay to the appropriate absolute versions        abstract TreeMap.Entry<K,V> subLowest();        abstract TreeMap.Entry<K,V> subHighest();        abstract TreeMap.Entry<K,V> subCeiling(K key);        abstract TreeMap.Entry<K,V> subHigher(K key);        abstract TreeMap.Entry<K,V> subFloor(K key);        abstract TreeMap.Entry<K,V> subLower(K key);        /** 返回升序迭代器from the perspective of this submap */        abstract Iterator<K> keyIterator();        abstract Spliterator<K> keySpliterator();        /** 返回降序迭代器from the perspective of this submap */        abstract Iterator<K> descendingKeyIterator();        // public methods        //如果fromStart、toEnd都是true，那么判断空、获取大小都是直接通过m，        //不然就必须使用entrySet()先获取结点集        public boolean isEmpty() {            return (fromStart && toEnd) ? m.isEmpty() : entrySet().isEmpty();        }        public int size() {            return (fromStart && toEnd) ? m.size() : entrySet().size();        }        //判断是否存在key先判断范围，再通过TreeMap的containsKey方法判断        public final boolean containsKey(Object key) {            return inRange(key) && m.containsKey(key);        }        //添加结点        public final V put(K key, V value) {        //判断要添加的key是否在范围内            if (!inRange(key))                throw new IllegalArgumentException("key out of range");            return m.put(key, value);        }        public final V get(Object key) {            return !inRange(key) ? null :  m.get(key);        }        public final V remove(Object key) {            return !inRange(key) ? null : m.remove(key);        }        public final Map.Entry<K,V> ceilingEntry(K key) {        //exportEntry(TreeMap.Entry<K,V> e)方法返回的是Map.Entry<K,V>对象        //它的key、value和传入结点的key、value相同            return exportEntry(subCeiling(key));        }        public final K ceilingKey(K key) {        //keyOrNull根据传入的结点是否是null返回null或返回结点的key（相当于提供了一个null安全的获取key的方法）            return keyOrNull(subCeiling(key));        }        public final Map.Entry<K,V> higherEntry(K key) {            return exportEntry(subHigher(key));        }        public final K higherKey(K key) {            return keyOrNull(subHigher(key));        }        public final Map.Entry<K,V> floorEntry(K key) {            return exportEntry(subFloor(key));        }        public final K floorKey(K key) {            return keyOrNull(subFloor(key));        }        public final Map.Entry<K,V> lowerEntry(K key) {            return exportEntry(subLower(key));        }        public final K lowerKey(K key) {            return keyOrNull(subLower(key));        }        public final K firstKey() {            return key(subLowest());        }        public final K lastKey() {            return key(subHighest());        }        public final Map.Entry<K,V> firstEntry() {            return exportEntry(subLowest());        }        public final Map.Entry<K,V> lastEntry() {            return exportEntry(subHighest());        }        //返回并删除第一个结点        public final Map.Entry<K,V> pollFirstEntry() {            TreeMap.Entry<K,V> e = subLowest();            Map.Entry<K,V> result = exportEntry(e);            if (e != null)                m.deleteEntry(e);            return result;        }        //返回并删除最后一个结点        public final Map.Entry<K,V> pollLastEntry() {            TreeMap.Entry<K,V> e = subHighest();            Map.Entry<K,V> result = exportEntry(e);            if (e != null)                m.deleteEntry(e);            return result;        }        // 视图        transient NavigableMap<K,V> descendingMapView = null;        transient EntrySetView entrySetView = null;        transient KeySet<K> navigableKeySetView = null;        //返回TreeMap的KeySet        public final NavigableSet<K> navigableKeySet() {            KeySet<K> nksv = navigableKeySetView;            return (nksv != null) ? nksv :                (navigableKeySetView = new TreeMap.KeySet<>(this));        }        public final Set<K> keySet() {            return navigableKeySet();        }        //逆序的KeySet        public NavigableSet<K> descendingKeySet() {            return descendingMap().navigableKeySet();        }        //返回一个子Map        public final SortedMap<K,V> subMap(K fromKey, K toKey) {            return subMap(fromKey, true, toKey, false);        }        public final SortedMap<K,V> headMap(K toKey) {            return headMap(toKey, false);        }        public final SortedMap<K,V> tailMap(K fromKey) {            return tailMap(fromKey, true);        }        // 视图类        abstract class EntrySetView extends AbstractSet<Map.Entry<K,V>> {            private transient int size = -1, sizeModCount;            //返回子Map的大小            public int size() {            //如果fromStart和toEnd都是true，返回的是m的Size                if (fromStart && toEnd)                    return m.size();                //size=-1或标记Size不同，重新计算一次size                if (size == -1 || sizeModCount != m.modCount) {                    sizeModCount = m.modCount;                    size = 0;                    Iterator<?> i = iterator();                    while (i.hasNext()) {                        size++;                        i.next();                    }                }                return size;            }            //判断EntrySet是否为空            public boolean isEmpty() {                TreeMap.Entry<K,V> n = absLowest();                return n == null || tooHigh(n.key);            }            //判断是否包含某个对象            public boolean contains(Object o) {                if (!(o instanceof Map.Entry))                    return false;                Map.Entry<?,?> entry = (Map.Entry<?,?>) o;                Object key = entry.getKey();                //key不在范围内，返回false                if (!inRange(key))                    return false;                //判断是否有键和值与传入结点的键和值相等的结点                TreeMap.Entry<?,?> node = m.getEntry(key);                return node != null &&                    valEquals(node.getValue(), entry.getValue());            }            //移除一个结点            public boolean remove(Object o) {                if (!(o instanceof Map.Entry))                    return false;                Map.Entry<?,?> entry = (Map.Entry<?,?>) o;                Object key = entry.getKey();                if (!inRange(key))                    return false;                TreeMap.Entry<K,V> node = m.getEntry(key);                if (node!=null && valEquals(node.getValue(),                                            entry.getValue())) {                    m.deleteEntry(node);                    return true;                }                return false;            }        }        /**         * 子类SubMaps迭代器         */        abstract class SubMapIterator<T> implements Iterator<T> {                  TreeMap.Entry<K,V> lastReturned;//上一次被返回的结点            TreeMap.Entry<K,V> next;//下一个结点            final Object fenceKey;//栅栏key（如果是向大的方向遍历，不能访问key大于等于fenceKey的结点            //如果是向小的方向遍历，不能访问key小于等于fenceKey的结点）            int expectedModCount;            //构造方法            SubMapIterator(TreeMap.Entry<K,V> first,                           TreeMap.Entry<K,V> fence) {                expectedModCount = m.modCount;                lastReturned = null;                next = first;                fenceKey = fence == null ? UNBOUNDED : fence.key;            }            //判断是否还有下一个结点            public final boolean hasNext() {            //与普通的hasNext的判断不同，这里必须判断next的key是否超出了fenceKey                return next != null && next.key != fenceKey;            }            //获取下一个结点            final TreeMap.Entry<K,V> nextEntry() {                TreeMap.Entry<K,V> e = next;                if (e == null || e.key == fenceKey)                    throw new NoSuchElementException();                if (m.modCount != expectedModCount)                    throw new ConcurrentModificationException();                next = successor(e);                lastReturned = e;                return e;            }            //返回前一个结点（向前遍历时）            final TreeMap.Entry<K,V> prevEntry() {                TreeMap.Entry<K,V> e = next;                if (e == null || e.key == fenceKey)                    throw new NoSuchElementException();                if (m.modCount != expectedModCount)                    throw new ConcurrentModificationException();                next = predecessor(e);                lastReturned = e;                return e;            }            //删除结点后可以继续遍历剩余的结点，因为删除前用next保留了lastReturned结点，            //而这个结点在删除操作的过程中被替换成了它的后继结点            final void removeAscending() {                if (lastReturned == null)                    throw new IllegalStateException();                if (m.modCount != expectedModCount)                    throw new ConcurrentModificationException();                // deleted entries are replaced by their successors                if (lastReturned.left != null && lastReturned.right != null)                //next指向lastReturned所指向的结点，这个结点的内容在删除lastReturned的时候被改变了                    next = lastReturned;                m.deleteEntry(lastReturned);                lastReturned = null;                expectedModCount = m.modCount;            }            //删除之后next指向的结点其实被删除了，不能继续迭代访问            final void removeDescending() {                if (lastReturned == null)                    throw new IllegalStateException();                if (m.modCount != expectedModCount)                    throw new ConcurrentModificationException();                m.deleteEntry(lastReturned);                lastReturned = null;                expectedModCount = m.modCount;            }        }        //下面是几个内部类，都是对SubMapIterator的调用或间接调用        final class SubMapEntryIterator extends SubMapIterator<Map.Entry<K,V>> {            SubMapEntryIterator(TreeMap.Entry<K,V> first,                                TreeMap.Entry<K,V> fence) {                super(first, fence);            }            public Map.Entry<K,V> next() {                return nextEntry();            }            public void remove() {                removeAscending();            }        }        final class DescendingSubMapEntryIterator extends SubMapIterator<Map.Entry<K,V>> {            DescendingSubMapEntryIterator(TreeMap.Entry<K,V> last,                                          TreeMap.Entry<K,V> fence) {                super(last, fence);            }            public Map.Entry<K,V> next() {                return prevEntry();            }            public void remove() {                removeDescending();            }        }        // Implement minimal Spliterator as KeySpliterator backup        final class SubMapKeyIterator extends SubMapIterator<K>            implements Spliterator<K> {            SubMapKeyIterator(TreeMap.Entry<K,V> first,                              TreeMap.Entry<K,V> fence) {                super(first, fence);            }            public K next() {                return nextEntry().key;            }            public void remove() {                removeAscending();            }            public Spliterator<K> trySplit() {                return null;            }            public void forEachRemaining(Consumer<? super K> action) {                while (hasNext())                    action.accept(next());            }            public boolean tryAdvance(Consumer<? super K> action) {                if (hasNext()) {                    action.accept(next());                    return true;                }                return false;            }            public long estimateSize() {                return Long.MAX_VALUE;            }            public int characteristics() {                return Spliterator.DISTINCT | Spliterator.ORDERED |                    Spliterator.SORTED;            }            public final Comparator<? super K>  getComparator() {                return NavigableSubMap.this.comparator();            }        }        final class DescendingSubMapKeyIterator extends SubMapIterator<K>            implements Spliterator<K> {            DescendingSubMapKeyIterator(TreeMap.Entry<K,V> last,                                        TreeMap.Entry<K,V> fence) {                super(last, fence);            }            public K next() {                return prevEntry().key;            }            public void remove() {                removeDescending();            }            public Spliterator<K> trySplit() {                return null;            }            public void forEachRemaining(Consumer<? super K> action) {                while (hasNext())                    action.accept(next());            }            public boolean tryAdvance(Consumer<? super K> action) {                if (hasNext()) {                    action.accept(next());                    return true;                }                return false;            }            public long estimateSize() {                return Long.MAX_VALUE;            }            public int characteristics() {                return Spliterator.DISTINCT | Spliterator.ORDERED;            }        }    }    /**     * AscendingSubMap继承自NavigableSubMap     */    static final class AscendingSubMap<K,V> extends NavigableSubMap<K,V> {        private static final long serialVersionUID = 912986545866124060L;        //构造方法，直接调用父类构造方法        AscendingSubMap(TreeMap<K,V> m,                        boolean fromStart, K lo, boolean loInclusive,                        boolean toEnd,     K hi, boolean hiInclusive) {            super(m, fromStart, lo, loInclusive, toEnd, hi, hiInclusive);        }        //获得比较器         public Comparator<? super K> comparator() {            return m.comparator();        }        //截取子Map        public NavigableMap<K,V> subMap(K fromKey, boolean fromInclusive,                                        K toKey,   boolean toInclusive) {        //截取之前判断是否超出范围            if (!inRange(fromKey, fromInclusive))                throw new IllegalArgumentException("fromKey out of range");            if (!inRange(toKey, toInclusive))                throw new IllegalArgumentException("toKey out of range");            return new AscendingSubMap<>(m,                                         false, fromKey, fromInclusive,                                         false, toKey,   toInclusive);        }        //截取子Map，headMap通过构造方法就可以实现        public NavigableMap<K,V> headMap(K toKey, boolean inclusive) {            if (!inRange(toKey, inclusive))                throw new IllegalArgumentException("toKey out of range");            return new AscendingSubMap<>(m,                                         fromStart, lo,    loInclusive,                                         false,     toKey, inclusive);        }        //tailMap        public NavigableMap<K,V> tailMap(K fromKey, boolean inclusive) {            if (!inRange(fromKey, inclusive))                throw new IllegalArgumentException("fromKey out of range");            return new AscendingSubMap<>(m,                                         false, fromKey, inclusive,                                         toEnd, hi,      hiInclusive);        }        public NavigableMap<K,V> descendingMap() {            NavigableMap<K,V> mv = descendingMapView;            return (mv != null) ? mv :                (descendingMapView =                 new DescendingSubMap<>(m,                                        fromStart, lo, loInclusive,                                        toEnd,     hi, hiInclusive));        }        Iterator<K> keyIterator() {            return new SubMapKeyIterator(absLowest(), absHighFence());        }        Spliterator<K> keySpliterator() {            return new SubMapKeyIterator(absLowest(), absHighFence());        }        Iterator<K> descendingKeyIterator() {            return new DescendingSubMapKeyIterator(absHighest(), absLowFence());        }        //AscendingEntrySetView是一个视图类，重写了父类的iterator()方法，        //调用SubMapEntryIterator构造迭代器         final class AscendingEntrySetView extends EntrySetView {            public Iterator<Map.Entry<K,V>> iterator() {                return new SubMapEntryIterator(absLowest(), absHighFence());            }        }        //获取结点集合的方法        public Set<Map.Entry<K,V>> entrySet() {            EntrySetView es = entrySetView;            return (es != null) ? es : (entrySetView = new AscendingEntrySetView());        }        //父类中抽象方法的实现        TreeMap.Entry<K,V> subLowest()       { return absLowest(); }        TreeMap.Entry<K,V> subHighest()      { return absHighest(); }        TreeMap.Entry<K,V> subCeiling(K key) { return absCeiling(key); }        TreeMap.Entry<K,V> subHigher(K key)  { return absHigher(key); }        TreeMap.Entry<K,V> subFloor(K key)   { return absFloor(key); }        TreeMap.Entry<K,V> subLower(K key)   { return absLower(key); }    }    /**     * DescendingSubMap也继承自NavigableSubMap     */    static final class DescendingSubMap<K,V>  extends NavigableSubMap<K,V> {        private static final long serialVersionUID = 912986545866120460L;        DescendingSubMap(TreeMap<K,V> m,                        boolean fromStart, K lo, boolean loInclusive,                        boolean toEnd,     K hi, boolean hiInclusive) {            super(m, fromStart, lo, loInclusive, toEnd, hi, hiInclusive);        }        //构造一个相反的比较器        private final Comparator<? super K> reverseComparator =            Collections.reverseOrder(m.comparator);        //获取的比较器是相反的比较器，比较结果会对调        public Comparator<? super K> comparator() {            return reverseComparator;        }        public NavigableMap<K,V> subMap(K fromKey, boolean fromInclusive,                                        K toKey,   boolean toInclusive) {            if (!inRange(fromKey, fromInclusive))                throw new IllegalArgumentException("fromKey out of range");            if (!inRange(toKey, toInclusive))                throw new IllegalArgumentException("toKey out of range");            return new DescendingSubMap<>(m,                                          false, toKey,   toInclusive,                                          false, fromKey, fromInclusive);        }        public NavigableMap<K,V> headMap(K toKey, boolean inclusive) {            if (!inRange(toKey, inclusive))                throw new IllegalArgumentException("toKey out of range");            //因为DescendingSubMap表示的是逆序的Map，所以其实是通过获取原序的尾部实现的            return new DescendingSubMap<>(m,                                          false, toKey, inclusive,                                          toEnd, hi,    hiInclusive);        }        //tailMap其实获取的是原序的头部        public NavigableMap<K,V> tailMap(K fromKey, boolean inclusive) {            if (!inRange(fromKey, inclusive))                throw new IllegalArgumentException("fromKey out of range");            return new DescendingSubMap<>(m,                                          fromStart, lo, loInclusive,                                          false, fromKey, inclusive);        }        //逆序的逆序其实是正序        public NavigableMap<K,V> descendingMap() {            NavigableMap<K,V> mv = descendingMapView;            return (mv != null) ? mv :                (descendingMapView =                 new AscendingSubMap<>(m,                                       fromStart, lo, loInclusive,                                       toEnd,     hi, hiInclusive));        }        Iterator<K> keyIterator() {            return new DescendingSubMapKeyIterator(absHighest(), absLowFence());        }        Spliterator<K> keySpliterator() {            return new DescendingSubMapKeyIterator(absHighest(), absLowFence());        }        Iterator<K> descendingKeyIterator() {            return new SubMapKeyIterator(absLowest(), absHighFence());        }        final class DescendingEntrySetView extends EntrySetView {            public Iterator<Map.Entry<K,V>> iterator() {                return new DescendingSubMapEntryIterator(absHighest(), absLowFence());            }        }        public Set<Map.Entry<K,V>> entrySet() {            EntrySetView es = entrySetView;            return (es != null) ? es : (entrySetView = new DescendingEntrySetView());        }        TreeMap.Entry<K,V> subLowest()       { return absHighest(); }        TreeMap.Entry<K,V> subHighest()      { return absLowest(); }        TreeMap.Entry<K,V> subCeiling(K key) { return absFloor(key); }        TreeMap.Entry<K,V> subHigher(K key)  { return absLower(key); }        TreeMap.Entry<K,V> subFloor(K key)   { return absCeiling(key); }        TreeMap.Entry<K,V> subLower(K key)   { return absHigher(key); }    }    /**     * SubMap 继承自AbstractMap；这个类存在仅仅为了序列化兼容之前的版本不支持NavigableMap TreeMap。     * 它被翻译成一个旧版本AscendingSubMap子映射到一个新版本。这个类是从来没有以其他方式使用。     */    private class SubMap extends AbstractMap<K,V>        implements SortedMap<K,V>, java.io.Serializable {        private static final long serialVersionUID = -6520786458950516097L;        //标识是否从Map的开始到结尾都属于子Map        private boolean fromStart = false, toEnd = false;        //开始位置和结束位置的key        private K fromKey, toKey;        private Object readResolve() {            return new AscendingSubMap<>(TreeMap.this,                                         fromStart, fromKey, true,                                         toEnd, toKey, false);        }        //虽然提供了这么多方法但是都不能用        public Set<Map.Entry<K,V>> entrySet() { throw new InternalError(); }        public K lastKey() { throw new InternalError(); }        public K firstKey() { throw new InternalError(); }        public SortedMap<K,V> subMap(K fromKey, K toKey) { throw new InternalError(); }        public SortedMap<K,V> headMap(K toKey) { throw new InternalError(); }        public SortedMap<K,V> tailMap(K fromKey) { throw new InternalError(); }        public Comparator<? super K> comparator() { throw new InternalError(); }    }    // 红黑树机制    private static final boolean RED   = false;    private static final boolean BLACK = true;    /**     * 树中结点的内部类Entry     */    static final class Entry<K,V> implements Map.Entry<K,V> {        K key;//关键字Key        V value;//值value        Entry<K,V> left = null;//左孩子        Entry<K,V> right = null;//右孩子        Entry<K,V> parent;//父节点        boolean color = BLACK;//红黑树的结点表示颜色的属性        /**         * 根据给定的键、值、父节点构造一个节点，颜色为默认的黑色         */        Entry(K key, V value, Entry<K,V> parent) {            this.key = key;            this.value = value;            this.parent = parent;        }        /**         * 获取结点的Key         */        public K getKey() {            return key;        }        /**         * 获取结点的value         */        public V getValue() {            return value;        }        /**         * 修改并返回当前节点的value         */        public V setValue(V value) {            V oldValue = this.value;            this.value = value;            return oldValue;        }        /**         * 判断结点相等的方法（两个结点为同一类型且Key值和value值都相等时两个结点相等）         */        public boolean equals(Object o) {            if (!(o instanceof Map.Entry))                return false;            Map.Entry<?,?> e = (Map.Entry<?,?>)o;            return valEquals(key,e.getKey()) && valEquals(value,e.getValue());        }        /**         * 结点的哈希值计算方法         * @return         */        public int hashCode() {            int keyHash = (key==null ? 0 : key.hashCode());            int valueHash = (value==null ? 0 : value.hashCode());            return keyHash ^ valueHash;        }        public String toString() {            return key + "=" + value;        }    }    /**     * 获取最左结点     */    final Entry<K,V> getFirstEntry() {        Entry<K,V> p = root;        if (p != null)            while (p.left != null)                p = p.left;        return p;    }    /**     * 获取最右结点     */    final Entry<K,V> getLastEntry() {        Entry<K,V> p = root;        if (p != null)            while (p.right != null)                p = p.right;        return p;    }    /**     * 返回指定结点的后继结点     */    static <K,V> TreeMap.Entry<K,V> successor(Entry<K,V> t) {    //如果t本身是一个空结点，返回null        if (t == null)            return null;        //如果t有右孩子，找到右孩子的最左子孙结点        else if (t.right != null) {            Entry<K,V> p = t.right;            //获取p结点最左的子孙结点，如果存在的话            while (p.left != null)                p = p.left;            return p;//返回找到的后继结点        } else {//t不为null且没有右孩子            Entry<K,V> p = t.parent;            Entry<K,V> ch = t;            //沿着右孩子向上查找后继结点，直到根节点或找到结点ch是其父节点的左孩子的结点            while (p != null && ch == p.right) {                ch = p;                p = p.parent;            }            return p;        }    }    /**       * 返回指定结点的前一个结点     */    static <K,V> Entry<K,V> predecessor(Entry<K,V> t) {        if (t == null)            return null;        else if (t.left != null) {        //获得左孩子            Entry<K,V> p = t.left;            //对左孩子进行遍历，获取左孩子最右的子孙            while (p.right != null)                p = p.right;            return p;        } else {        //获取t的父节点            Entry<K,V> p = t.parent;            Entry<K,V> ch = t;            //沿着右孩子向上查找后继结点，直到根节点或找到结点ch是其父节点的右孩子的结点            while (p != null && ch == p.left) {                ch = p;                p = p.parent;            }            return p;        }    }    /**     * 平衡相关操作.     *     * Implementations of rebalancings during insertion and deletion are     * slightly different than the CLR version.  Rather than using dummy     * nilnodes, we use a set of accessors that deal properly with null.  They     * are used to avoid messiness surrounding nullness checks in the main     * algorithms.     */    private static <K,V> boolean colorOf(Entry<K,V> p) {        return (p == null ? BLACK : p.color);    }    private static <K,V> Entry<K,V> parentOf(Entry<K,V> p) {        return (p == null ? null: p.parent);    }    private static <K,V> void setColor(Entry<K,V> p, boolean c) {        if (p != null)            p.color = c;    }    private static <K,V> Entry<K,V> leftOf(Entry<K,V> p) {        return (p == null) ? null: p.left;    }    private static <K,V> Entry<K,V> rightOf(Entry<K,V> p) {        return (p == null) ? null: p.right;    }    /** 左旋 */    private void rotateLeft(Entry<K,V> p) {        if (p != null) {            Entry<K,V> r = p.right;            p.right = r.left;            if (r.left != null)                r.left.parent = p;            r.parent = p.parent;            if (p.parent == null)                root = r;            else if (p.parent.left == p)                p.parent.left = r;            else                p.parent.right = r;            r.left = p;            p.parent = r;        }    }    /** 右旋 */    private void rotateRight(Entry<K,V> p) {        if (p != null) {            Entry<K,V> l = p.left;            p.left = l.right;            if (l.right != null) l.right.parent = p;            l.parent = p.parent;            if (p.parent == null)                root = l;            else if (p.parent.right == p)                p.parent.right = l;            else p.parent.left = l;            l.right = p;            p.parent = l;        }    }    //负责在插入结点后调整树结构和着色，以满足红黑树的要求    private void fixAfterInsertion(Entry<K,V> x) {    //插入结点默认为红色        x.color = RED;        //循环条件是x不为空、不是根节点、父节点的颜色是红色（如果父节点不是红色，则没有连续的红色结点，不再调整）        while (x != null && x != root && x.parent.color == RED) {        //x结点的父节点p是其父节点pp（p的父节点）的左孩子            if (parentOf(x) == leftOf(parentOf(parentOf(x)))) {            //获取pp结点的右孩子r                Entry<K,V> y = rightOf(parentOf(parentOf(x)));                //pp右孩子的颜色是红色（colorOf(Entry e)方法在e为空时返回black），不需要进行旋转操作                //（因为红黑树不是严格的平衡二叉树）                if (colorOf(y) == RED) {                //将x的父节点设置为黑色                    setColor(parentOf(x), BLACK);                    //y结点，即pp结点的右孩子r设置成黑色                    setColor(y, BLACK);                    //pp结点设置成红色                    setColor(parentOf(parentOf(x)), RED);                    //x移动到pp结点                    x = parentOf(parentOf(x));                } else {                //父亲的兄弟是黑色的，这时需要进行旋转操作，根据是“内部”还是“外部”的情况决定是双旋转还是单旋转                //x结点是父节点的右孩子（因为上面已经确认p是pp的左孩子，所以这是一个“内部 ，左-右”插入的情况，需要进行双旋转处理）                    if (x == rightOf(parentOf(x))) {                    //x移动到它的父节点                        x = parentOf(x);                        //左旋操作                        rotateLeft(x);                    }                    //x的父节点设置成黑色                    setColor(parentOf(x), BLACK);                    //x的父节点的父节点设置成红色                    setColor(parentOf(parentOf(x)), RED);                    //右旋操作                    rotateRight(parentOf(parentOf(x)));                }            } else {            //获取x的父节点p的父节点pp的左孩子y                Entry<K,V> y = leftOf(parentOf(parentOf(x)));                //y结点是红色的                if (colorOf(y) == RED) {                //x的父节点，即p结点，设置成黑色                    setColor(parentOf(x), BLACK);                    //y结点设置成黑色                    setColor(y, BLACK);                    //pp结点设置成红色                    setColor(parentOf(parentOf(x)), RED);                    //x移动到pp结点                    x = parentOf(parentOf(x));                } else {                //x是父节点的左孩子（因为上面已经确认p是pp的右孩子，所以这是一个“内部，右-左”插入的情况，需要进行双旋转处理）                    if (x == leftOf(parentOf(x))) {                    //x移动到父节点                        x = parentOf(x);                        //右旋操作                        rotateRight(x);                    }                    //x的父节点设置成黑色                    setColor(parentOf(x), BLACK);                    //x的父节点的父节点设置成红色                    setColor(parentOf(parentOf(x)), RED);                    //左旋操作                    rotateLeft(parentOf(parentOf(x)));                }            }        }        //根节点为黑色        root.color = BLACK;    }    /**     * 删除结点p，并重新平衡树     */    private void deleteEntry(Entry<K,V> p) {    //记录树结构的修改次数        modCount++;        //记录树中结点的个数        size--;        //p有左右两个孩子的情况，标记为第一种        // 如果是严格意义上的内部情况，将p的后继复制到p中，然后让p指向后继结点         if (p.left != null && p.right != null) {        //获取后继结点（有两个孩子的情况下，后继结点肯定是右孩子或者右孩子的最左子孙）            Entry<K,V> s = successor(p);            //使用后继结点s替换要被删除的结点p,将后继结点的Key和value复制到p结点，之后将p指向后继结点            p.key = s.key;            p.value = s.value;            p = s;        } // p has 2 children        // Start fixup at replacement node, if it exists.        //开始修复被移除结点处的树结构        //如果p有左孩子，取左孩子，否则取右孩子，标记为第二种情况        Entry<K,V> replacement = (p.left != null ? p.left : p.right);        if (replacement != null) {            // Link replacement to parent            replacement.parent = p.parent;            //如果p结点没有父节点，即p结点是根节点            if (p.parent == null)            //将根节点替换为replacement结点                root = replacement;            //p是其父节点的左孩子            else if (p == p.parent.left)            //将p的父节点的left引用指向replacement            //这步操作实现了删除p的父节点到p结点的引用                p.parent.left  = replacement;            else            //如果p是其父节点的右孩子，将父节点的right引用指向replacement                p.parent.right = replacement;            // Null out links so they are OK to use by fixAfterDeletion.            //解除p结点到其左右孩子和父节点的引用             p.left = p.right = p.parent = null;            // Fix replacement            if (p.color == BLACK)            //在删除结点后修复红黑树的颜色分配                fixAfterDeletion(replacement);        } else if (p.parent == null) { // return if we are the only node.        //进入这块代码说明p结点就是根节点        //如果标记第一种处p有左右孩子，则找到的后继结点s是p的一个祖先结点或右孩子或右孩子的最左子孙结点，        //他们要么有孩子结点，要么有父节点，所以如果进入这段代码，则说明标记第一种处的p结点没有左右两个孩子。        //没有左右孩子，则分没有孩子、有一个右孩子、有一个左孩子三种情况，只没有孩子的情况会使标记第一种的if判断不通过，        //所以p结点只能是没有孩子，加上这里的判断，p没有父节点，所以p是一个独立结点，也是树中的唯一结点        //所以将根节点设置为null即实现了对该结点的删除            root = null;        } else { //  No children. Use self as phantom replacement and unlink.            if (p.color == BLACK)            //调整树结构                fixAfterDeletion(p);            //这个判断也一定会通过，因为p.parent如果是null，则在上面的else if块中已经被处理            if (p.parent != null) {            //p是一个左孩子                if (p == p.parent.left)                //删除父节点对p的引用                    p.parent.left = null;                else if (p == p.parent.right) //p是一个右孩子                //删除父节点对p的引用                    p.parent.right = null;                //删除p结点对父节点的引用                p.parent = null;            }        }    }    /**      * 删除之后的修复操作     */    private void fixAfterDeletion(Entry<K,V> x) {    //循环处理，条件为x不是root结点且是黑色的（因为红色不会对红黑树的性质造成破坏，所以不需要调整）        while (x != root && colorOf(x) == BLACK) {        //x是一个左孩子            if (x == leftOf(parentOf(x))) {            //获取x的兄弟结点sib                Entry<K,V> sib = rightOf(parentOf(x));                //sib是红色的                if (colorOf(sib) == RED) {                //将sib设置成黑色                    setColor(sib, BLACK);                    //将父节点设置成红色                    setColor(parentOf(x), RED);                    //左旋父节点                    rotateLeft(parentOf(x));                    //sib移动到旋转后x的父节点p的右孩子                    sib = rightOf(parentOf(x));                }                //sib的两个孩子的颜色都是黑色（null返回黑色）                if (colorOf(leftOf(sib))  == BLACK &&                    colorOf(rightOf(sib)) == BLACK) {                //将sib设置成红色                    setColor(sib, RED);                    //x移动到x的父节点                    x = parentOf(x);                } else {//sib的左右孩子都是黑色的不成立                //sib的右孩子是黑色的                    if (colorOf(rightOf(sib)) == BLACK) {                    //将sib的左孩子设置成黑色                        setColor(leftOf(sib), BLACK);                        //sib结点设置成红色                        setColor(sib, RED);                        //右旋操作                        rotateRight(sib);                        //sib移动到旋转后x父节点的右孩子                        sib = rightOf(parentOf(x));                    }                    //sib设置成和x的父节点一样的颜色                    setColor(sib, colorOf(parentOf(x)));                    //x的父节点设置成黑色                    setColor(parentOf(x), BLACK);                    //sib的右孩子设置成黑色                    setColor(rightOf(sib), BLACK);                    //左旋操作                    rotateLeft(parentOf(x));                    //设置调整完的条件： x = root 跳出循环                    x = root;                }            } else { // 对称情况，x是一个右孩子            //获取x的兄弟结点                Entry<K,V> sib = leftOf(parentOf(x));                //如果sib是红色的                if (colorOf(sib) == RED) {                //将sib设置为黑色                    setColor(sib, BLACK);                    //将x的父节点设置成红色                    setColor(parentOf(x), RED);                    //右旋                    rotateRight(parentOf(x));                    //sib移动到旋转后x父节点的左孩子                    sib = leftOf(parentOf(x));                }                //sib的两个孩子的颜色都是黑色（null返回黑色）                if (colorOf(rightOf(sib)) == BLACK &&                    colorOf(leftOf(sib)) == BLACK) {                //sib设置为红色                    setColor(sib, RED);                    //x移动到x的父节点                    x = parentOf(x);                } else {//sib的两个孩子的颜色都是黑色（null返回黑色） 不成立                //sib的左孩子是黑色的，或者没有左孩子                    if (colorOf(leftOf(sib)) == BLACK) {                    //将sib的右孩子设置成黑色                        setColor(rightOf(sib), BLACK);                        //sib结点设置成红色                        setColor(sib, RED);                        //左旋                        rotateLeft(sib);                        //sib移动到x父节点的左孩子                        sib = leftOf(parentOf(x));                    }                    //sib设置成和x的父节点一个颜色                    setColor(sib, colorOf(parentOf(x)));                    //x的父节点设置成黑色                    setColor(parentOf(x), BLACK);                    //sib的左孩子设置成黑色                    setColor(leftOf(sib), BLACK);                    //右旋                    rotateRight(parentOf(x));                    //设置跳出循环的标识                    x = root;                }            }        }        //将x设置为黑色        setColor(x, BLACK);    }    private static final long serialVersionUID = 919286545866124006L;    /**     * Save the state of the {@code TreeMap} instance to a stream (i.e.,     * serialize it).     *     * @serialData The <em>size</em> of the TreeMap (the number of key-value     *             mappings) is emitted (int), followed by the key (Object)     *             and value (Object) for each key-value mapping represented     *             by the TreeMap. The key-value mappings are emitted in     *             key-order (as determined by the TreeMap's Comparator,     *             or by the keys' natural ordering if the TreeMap has no     *             Comparator).     */    private void writeObject(java.io.ObjectOutputStream s)        throws java.io.IOException {        // Write out the Comparator and any hidden stuff        s.defaultWriteObject();        // Write out size (number of Mappings)        s.writeInt(size);        // Write out keys and values (alternating)        for (Iterator<Map.Entry<K,V>> i = entrySet().iterator(); i.hasNext(); ) {            Map.Entry<K,V> e = i.next();            s.writeObject(e.getKey());            s.writeObject(e.getValue());        }    }    /**     * Reconstitute the {@code TreeMap} instance from a stream (i.e.,     * deserialize it).     */    private void readObject(final java.io.ObjectInputStream s)        throws java.io.IOException, ClassNotFoundException {        // Read in the Comparator and any hidden stuff        s.defaultReadObject();        // Read in size        int size = s.readInt();        buildFromSorted(size, null, s, null);    }    /** Intended to be called only from TreeSet.readObject */    void readTreeSet(int size, java.io.ObjectInputStream s, V defaultVal)        throws java.io.IOException, ClassNotFoundException {        buildFromSorted(size, null, s, defaultVal);    }    /** Intended to be called only from TreeSet.addAll */    void addAllForTreeSet(SortedSet<? extends K> set, V defaultVal) {        try {            buildFromSorted(set.size(), set.iterator(), null, defaultVal);        } catch (java.io.IOException cannotHappen) {        } catch (ClassNotFoundException cannotHappen) {        }    }    /**     * Linear time tree building algorithm from sorted data.  Can accept keys     * and/or values from iterator or stream. This leads to too many     * parameters, but seems better than alternatives.  The four formats     * that this method accepts are:     *     *    1) An iterator of Map.Entries.  (it != null, defaultVal == null).     *    2) An iterator of keys.         (it != null, defaultVal != null).     *    3) A stream of alternating serialized keys and values.     *                                   (it == null, defaultVal == null).     *    4) A stream of serialized keys. (it == null, defaultVal != null).     *     * It is assumed that the comparator of the TreeMap is already set prior     * to calling this method.     *     * @param size the number of keys (or key-value pairs) to be read from     *        the iterator or stream     * @param it If non-null, new entries are created from entries     *        or keys read from this iterator.     * @param str If non-null, new entries are created from keys and     *        possibly values read from this stream in serialized form.     *        Exactly one of it and str should be non-null.     * @param defaultVal if non-null, this default value is used for     *        each value in the map.  If null, each value is read from     *        iterator or stream, as described above.     * @throws java.io.IOException propagated from stream reads. This cannot     *         occur if str is null.     * @throws ClassNotFoundException propagated from readObject.     *         This cannot occur if str is null.     */    private void buildFromSorted(int size, Iterator<?> it,                                 java.io.ObjectInputStream str,                                 V defaultVal)        throws  java.io.IOException, ClassNotFoundException {        this.size = size;        root = buildFromSorted(0, 0, size-1, computeRedLevel(size),                               it, str, defaultVal);    }    /**     * Recursive "helper method" that does the real work of the     * previous method.  Identically named parameters have     * identical definitions.  Additional parameters are documented below.     * It is assumed that the comparator and size fields of the TreeMap are     * already set prior to calling this method.  (It ignores both fields.)     *     * @param level the current level of tree. Initial call should be 0.     * @param lo the first element index of this subtree. Initial should be 0.     * @param hi the last element index of this subtree.  Initial should be     *        size-1.     * @param redLevel the level at which nodes should be red.     *        Must be equal to computeRedLevel for tree of this size.     */    @SuppressWarnings("unchecked")    private final Entry<K,V> buildFromSorted(int level, int lo, int hi,                                             int redLevel,                                             Iterator<?> it,                                             java.io.ObjectInputStream str,                                             V defaultVal)        throws  java.io.IOException, ClassNotFoundException {        /*         * Strategy: The root is the middlemost element. To get to it, we         * have to first recursively construct the entire left subtree,         * so as to grab all of its elements. We can then proceed with right         * subtree.         *         * The lo and hi arguments are the minimum and maximum         * indices to pull out of the iterator or stream for current subtree.         * They are not actually indexed, we just proceed sequentially,         * ensuring that items are extracted in corresponding order.         */        if (hi < lo) return null;        int mid = (lo + hi) >>> 1;        Entry<K,V> left  = null;        if (lo < mid)            left = buildFromSorted(level+1, lo, mid - 1, redLevel,                                   it, str, defaultVal);        // extract key and/or value from iterator or stream        K key;        V value;        if (it != null) {            if (defaultVal==null) {                Map.Entry<?,?> entry = (Map.Entry<?,?>)it.next();                key = (K)entry.getKey();                value = (V)entry.getValue();            } else {                key = (K)it.next();                value = defaultVal;            }        } else { // use stream            key = (K) str.readObject();            value = (defaultVal != null ? defaultVal : (V) str.readObject());        }        Entry<K,V> middle =  new Entry<>(key, value, null);        // color nodes in non-full bottommost level red        if (level == redLevel)            middle.color = RED;        if (left != null) {            middle.left = left;            left.parent = middle;        }        if (mid < hi) {            Entry<K,V> right = buildFromSorted(level+1, mid+1, hi, redLevel,                                               it, str, defaultVal);            middle.right = right;            right.parent = middle;        }        return middle;    }    /**     * Find the level down to which to assign all nodes BLACK.  This is the     * last `full' level of the complete binary tree produced by     * buildTree. The remaining nodes are colored RED. (This makes a `nice'     * set of color assignments wrt future insertions.) This level number is     * computed by finding the number of splits needed to reach the zeroeth     * node.  (The answer is ~lg(N), but in any case must be computed by same     * quick O(lg(N)) loop.)     */    private static int computeRedLevel(int sz) {        int level = 0;        for (int m = sz - 1; m >= 0; m = m / 2 - 1)            level++;        return level;    }    /**     * Currently, we support Spliterator-based versions only for the     * full map, in either plain of descending form, otherwise relying     * on defaults because size estimation for submaps would dominate     * costs. The type tests needed to check these for key views are     * not very nice but avoid disrupting existing class     * structures. Callers must use plain default spliterators if this     * returns null.     */    static <K> Spliterator<K> keySpliteratorFor(NavigableMap<K,?> m) {        if (m instanceof TreeMap) {            @SuppressWarnings("unchecked") TreeMap<K,Object> t =                (TreeMap<K,Object>) m;            return t.keySpliterator();        }        if (m instanceof DescendingSubMap) {            @SuppressWarnings("unchecked") DescendingSubMap<K,?> dm =                (DescendingSubMap<K,?>) m;            TreeMap<K,?> tm = dm.m;            if (dm == tm.descendingMap) {                @SuppressWarnings("unchecked") TreeMap<K,Object> t =                    (TreeMap<K,Object>) tm;                return t.descendingKeySpliterator();            }        }        @SuppressWarnings("unchecked") NavigableSubMap<K,?> sm =            (NavigableSubMap<K,?>) m;        return sm.keySpliterator();    }    final Spliterator<K> keySpliterator() {        return new KeySpliterator<K,V>(this, null, null, 0, -1, 0);    }    final Spliterator<K> descendingKeySpliterator() {        return new DescendingKeySpliterator<K,V>(this, null, null, 0, -2, 0);    }    /**     * Base class for spliterators.  Iteration starts at a given     * origin and continues up to but not including a given fence (or     * null for end).  At top-level, for ascending cases, the first     * split uses the root as left-fence/right-origin. From there,     * right-hand splits replace the current fence with its left     * child, also serving as origin for the split-off spliterator.     * Left-hands are symmetric. Descending versions place the origin     * at the end and invert ascending split rules.  This base class     * is non-commital about directionality, or whether the top-level     * spliterator covers the whole tree. This means that the actual     * split mechanics are located in subclasses. Some of the subclass     * trySplit methods are identical (except for return types), but     * not nicely factorable.     *     * Currently, subclass versions exist only for the full map     * (including descending keys via its descendingMap).  Others are     * possible but currently not worthwhile because submaps require     * O(n) computations to determine size, which substantially limits     * potential speed-ups of using custom Spliterators versus default     * mechanics.     *     * To boostrap initialization, external constructors use     * negative size estimates: -1 for ascend, -2 for descend.     */    static class TreeMapSpliterator<K,V> {        final TreeMap<K,V> tree;        TreeMap.Entry<K,V> current; // traverser; initially first node in range        TreeMap.Entry<K,V> fence;   // one past last, or null        int side;                   // 0: top, -1: is a left split, +1: right        int est;                    // size estimate (exact only for top-level)        int expectedModCount;       // for CME checks        TreeMapSpliterator(TreeMap<K,V> tree,                           TreeMap.Entry<K,V> origin, TreeMap.Entry<K,V> fence,                           int side, int est, int expectedModCount) {            this.tree = tree;            this.current = origin;            this.fence = fence;            this.side = side;            this.est = est;            this.expectedModCount = expectedModCount;        }        final int getEstimate() { // force initialization            int s; TreeMap<K,V> t;            if ((s = est) < 0) {                if ((t = tree) != null) {                    current = (s == -1) ? t.getFirstEntry() : t.getLastEntry();                    s = est = t.size;                    expectedModCount = t.modCount;                }                else                    s = est = 0;            }            return s;        }        public final long estimateSize() {            return (long)getEstimate();        }    }    static final class KeySpliterator<K,V>        extends TreeMapSpliterator<K,V>        implements Spliterator<K> {        KeySpliterator(TreeMap<K,V> tree,                       TreeMap.Entry<K,V> origin, TreeMap.Entry<K,V> fence,                       int side, int est, int expectedModCount) {            super(tree, origin, fence, side, est, expectedModCount);        }        public KeySpliterator<K,V> trySplit() {            if (est < 0)                getEstimate(); // force initialization            int d = side;            TreeMap.Entry<K,V> e = current, f = fence,                s = ((e == null || e == f) ? null :      // empty                     (d == 0)              ? tree.root : // was top                     (d >  0)              ? e.right :   // was right                     (d <  0 && f != null) ? f.left :    // was left                     null);            if (s != null && s != e && s != f &&                tree.compare(e.key, s.key) < 0) {        // e not already past s                side = 1;                return new KeySpliterator<>                    (tree, e, current = s, -1, est >>>= 1, expectedModCount);            }            return null;        }        public void forEachRemaining(Consumer<? super K> action) {            if (action == null)                throw new NullPointerException();            if (est < 0)                getEstimate(); // force initialization            TreeMap.Entry<K,V> f = fence, e, p, pl;            if ((e = current) != null && e != f) {                current = f; // exhaust                do {                    action.accept(e.key);                    if ((p = e.right) != null) {                        while ((pl = p.left) != null)                            p = pl;                    }                    else {                        while ((p = e.parent) != null && e == p.right)                            e = p;                    }                } while ((e = p) != null && e != f);                if (tree.modCount != expectedModCount)                    throw new ConcurrentModificationException();            }        }        public boolean tryAdvance(Consumer<? super K> action) {            TreeMap.Entry<K,V> e;            if (action == null)                throw new NullPointerException();            if (est < 0)                getEstimate(); // force initialization            if ((e = current) == null || e == fence)                return false;            current = successor(e);            action.accept(e.key);            if (tree.modCount != expectedModCount)                throw new ConcurrentModificationException();            return true;        }        public int characteristics() {            return (side == 0 ? Spliterator.SIZED : 0) |                Spliterator.DISTINCT | Spliterator.SORTED | Spliterator.ORDERED;        }        public final Comparator<? super K>  getComparator() {            return tree.comparator;        }    }    static final class DescendingKeySpliterator<K,V>        extends TreeMapSpliterator<K,V>        implements Spliterator<K> {        DescendingKeySpliterator(TreeMap<K,V> tree,                                 TreeMap.Entry<K,V> origin, TreeMap.Entry<K,V> fence,                                 int side, int est, int expectedModCount) {            super(tree, origin, fence, side, est, expectedModCount);        }        public DescendingKeySpliterator<K,V> trySplit() {            if (est < 0)                getEstimate(); // force initialization            int d = side;            TreeMap.Entry<K,V> e = current, f = fence,                    s = ((e == null || e == f) ? null :      // empty                         (d == 0)              ? tree.root : // was top                         (d <  0)              ? e.left :    // was left                         (d >  0 && f != null) ? f.right :   // was right                         null);            if (s != null && s != e && s != f &&                tree.compare(e.key, s.key) > 0) {       // e not already past s                side = 1;                return new DescendingKeySpliterator<>                        (tree, e, current = s, -1, est >>>= 1, expectedModCount);            }            return null;        }        public void forEachRemaining(Consumer<? super K> action) {            if (action == null)                throw new NullPointerException();            if (est < 0)                getEstimate(); // force initialization            TreeMap.Entry<K,V> f = fence, e, p, pr;            if ((e = current) != null && e != f) {                current = f; // exhaust                do {                    action.accept(e.key);                    if ((p = e.left) != null) {                        while ((pr = p.right) != null)                            p = pr;                    }                    else {                        while ((p = e.parent) != null && e == p.left)                            e = p;                    }                } while ((e = p) != null && e != f);                if (tree.modCount != expectedModCount)                    throw new ConcurrentModificationException();            }        }        public boolean tryAdvance(Consumer<? super K> action) {            TreeMap.Entry<K,V> e;            if (action == null)                throw new NullPointerException();            if (est < 0)                getEstimate(); // force initialization            if ((e = current) == null || e == fence)                return false;            current = predecessor(e);            action.accept(e.key);            if (tree.modCount != expectedModCount)                throw new ConcurrentModificationException();            return true;        }        public int characteristics() {            return (side == 0 ? Spliterator.SIZED : 0) |                Spliterator.DISTINCT | Spliterator.ORDERED;        }    }    static final class ValueSpliterator<K,V>            extends TreeMapSpliterator<K,V>            implements Spliterator<V> {        ValueSpliterator(TreeMap<K,V> tree,                         TreeMap.Entry<K,V> origin, TreeMap.Entry<K,V> fence,                         int side, int est, int expectedModCount) {            super(tree, origin, fence, side, est, expectedModCount);        }        public ValueSpliterator<K,V> trySplit() {            if (est < 0)                getEstimate(); // force initialization            int d = side;            TreeMap.Entry<K,V> e = current, f = fence,                    s = ((e == null || e == f) ? null :      // empty                         (d == 0)              ? tree.root : // was top                         (d >  0)              ? e.right :   // was right                         (d <  0 && f != null) ? f.left :    // was left                         null);            if (s != null && s != e && s != f &&                tree.compare(e.key, s.key) < 0) {        // e not already past s                side = 1;                return new ValueSpliterator<>                        (tree, e, current = s, -1, est >>>= 1, expectedModCount);            }            return null;        }        public void forEachRemaining(Consumer<? super V> action) {            if (action == null)                throw new NullPointerException();            if (est < 0)                getEstimate(); // force initialization            TreeMap.Entry<K,V> f = fence, e, p, pl;            if ((e = current) != null && e != f) {                current = f; // exhaust                do {                    action.accept(e.value);                    if ((p = e.right) != null) {                        while ((pl = p.left) != null)                            p = pl;                    }                    else {                        while ((p = e.parent) != null && e == p.right)                            e = p;                    }                } while ((e = p) != null && e != f);                if (tree.modCount != expectedModCount)                    throw new ConcurrentModificationException();            }        }        public boolean tryAdvance(Consumer<? super V> action) {            TreeMap.Entry<K,V> e;            if (action == null)                throw new NullPointerException();            if (est < 0)                getEstimate(); // force initialization            if ((e = current) == null || e == fence)                return false;            current = successor(e);            action.accept(e.value);            if (tree.modCount != expectedModCount)                throw new ConcurrentModificationException();            return true;        }        public int characteristics() {            return (side == 0 ? Spliterator.SIZED : 0) | Spliterator.ORDERED;        }    }    static final class EntrySpliterator<K,V>        extends TreeMapSpliterator<K,V>        implements Spliterator<Map.Entry<K,V>> {        EntrySpliterator(TreeMap<K,V> tree,                         TreeMap.Entry<K,V> origin, TreeMap.Entry<K,V> fence,                         int side, int est, int expectedModCount) {            super(tree, origin, fence, side, est, expectedModCount);        }        public EntrySpliterator<K,V> trySplit() {            if (est < 0)                getEstimate(); // force initialization            int d = side;            TreeMap.Entry<K,V> e = current, f = fence,                    s = ((e == null || e == f) ? null :      // empty                         (d == 0)              ? tree.root : // was top                         (d >  0)              ? e.right :   // was right                         (d <  0 && f != null) ? f.left :    // was left                         null);            if (s != null && s != e && s != f &&                tree.compare(e.key, s.key) < 0) {        // e not already past s                side = 1;                return new EntrySpliterator<>                        (tree, e, current = s, -1, est >>>= 1, expectedModCount);            }            return null;        }        public void forEachRemaining(Consumer<? super Map.Entry<K, V>> action) {            if (action == null)                throw new NullPointerException();            if (est < 0)                getEstimate(); // force initialization            TreeMap.Entry<K,V> f = fence, e, p, pl;            if ((e = current) != null && e != f) {                current = f; // exhaust                do {                    action.accept(e);                    if ((p = e.right) != null) {                        while ((pl = p.left) != null)                            p = pl;                    }                    else {                        while ((p = e.parent) != null && e == p.right)                            e = p;                    }                } while ((e = p) != null && e != f);                if (tree.modCount != expectedModCount)                    throw new ConcurrentModificationException();            }        }        public boolean tryAdvance(Consumer<? super Map.Entry<K,V>> action) {            TreeMap.Entry<K,V> e;            if (action == null)                throw new NullPointerException();            if (est < 0)                getEstimate(); // force initialization            if ((e = current) == null || e == fence)                return false;            current = successor(e);            action.accept(e);            if (tree.modCount != expectedModCount)                throw new ConcurrentModificationException();            return true;        }        public int characteristics() {            return (side == 0 ? Spliterator.SIZED : 0) |                    Spliterator.DISTINCT | Spliterator.SORTED | Spliterator.ORDERED;        }        @Override        public Comparator<Map.Entry<K, V>> getComparator() {            // Adapt or create a key-based comparator            if (tree.comparator != null) {                return Map.Entry.comparingByKey(tree.comparator);            }            else {                return (Comparator<Map.Entry<K, V>> & Serializable) (e1, e2) -> {                    @SuppressWarnings("unchecked")                    Comparable<? super K> k1 = (Comparable<? super K>) e1.getKey();                    return k1.compareTo(e2.getKey());                };            }        }    }}