Class - java.util.TreeMap
Created by : Mr Dk.
2019 / 11 / 14 10:43
Nanjing, Jiangsu, China
Definition
public class TreeMap<K,V>
extends AbstractMap<K,V>
implements NavigableMap<K,V>, Cloneable, java.io.Serializable
{
}
基于红黑树实现的 NavigableMap，Map 基于自然顺序或构造时提供的 Comparator 进行排序。对于下列操作保证 log(n) 的时间复杂度：
containsKey()get()put()remove()
对于 Map 接口来说，操作使用 equals() 函数；对于 SortedMap 接口来说，操作使用 compareTo() 函数。
TreeMap 的实现是不同步的，要么封装该集合对象负责实现同步，要么就用 Collections.synchronizedSortedMap(new TreeMap(...)) 来封装。
在迭代器迭代过程中，如果 Map 发生结构修改，则会立刻抛出错误，除非使用迭代器自己的 remove()。
所有函数中返回的 Map.Entry<> 都是映射的快照：不支持 Entry.setValue()，只能使用 put() 来改变映射。
/**
* A Red-Black tree based {@link NavigableMap} implementation.
* The map is sorted according to the {@linkplain Comparable natural
* ordering} of its keys, or by a {@link Comparator} provided at map
* creation time, depending on which constructor is used.
*
* <p>This implementation provides guaranteed log(n) time cost for the
* {@code containsKey}, {@code get}, {@code put} and {@code remove}
* operations. Algorithms are adaptations of those in Cormen, Leiserson, and
* Rivest's <em>Introduction to Algorithms</em>.
*
* <p>Note that the ordering maintained by a tree map, like any sorted map, and
* whether or not an explicit comparator is provided, must be <em>consistent
* with {@code equals}</em> if this sorted map is to correctly implement the
* {@code Map} interface. (See {@code Comparable} or {@code Comparator} for a
* precise definition of <em>consistent with equals</em>.) This is so because
* the {@code Map} interface is defined in terms of the {@code equals}
* operation, but a sorted map performs all key comparisons using its {@code
* compareTo} (or {@code compare}) method, so two keys that are deemed equal by
* this method are, from the standpoint of the sorted map, equal. The behavior
* of a sorted map <em>is</em> well-defined even if its ordering is
* inconsistent with {@code equals}; it just fails to obey the general contract
* of the {@code Map} interface.
*
* <p><strong>Note that this implementation is not synchronized.</strong>
* If multiple threads access a map concurrently, and at least one of the
* threads modifies the map structurally, it <em>must</em> be synchronized
* externally. (A structural modification is any operation that adds or
* deletes one or more mappings; merely changing the value associated
* with an existing key is not a structural modification.) This is
* typically accomplished by synchronizing on some object that naturally
* encapsulates the map.
* If no such object exists, the map should be "wrapped" using the
* {@link Collections#synchronizedSortedMap Collections.synchronizedSortedMap}
* method. This is best done at creation time, to prevent accidental
* unsynchronized access to the map: <pre>
* SortedMap m = Collections.synchronizedSortedMap(new TreeMap(...));</pre>
*
* <p>The iterators returned by the {@code iterator} method of the collections
* returned by all of this class's "collection view methods" are
* <em>fail-fast</em>: if the map is structurally modified at any time after
* the iterator is created, in any way except through the iterator's own
* {@code remove} method, the iterator will throw a {@link
* ConcurrentModificationException}. Thus, in the face of concurrent
* modification, the iterator fails quickly and cleanly, rather than risking
* arbitrary, non-deterministic behavior at an undetermined time in the future.
*
* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
* as it is, generally speaking, impossible to make any hard guarantees in the
* presence of unsynchronized concurrent modification. Fail-fast iterators
* throw {@code ConcurrentModificationException} on a best-effort basis.
* Therefore, it would be wrong to write a program that depended on this
* exception for its correctness: <em>the fail-fast behavior of iterators
* should be used only to detect bugs.</em>
*
* <p>All {@code Map.Entry} pairs returned by methods in this class
* and its views represent snapshots of mappings at the time they were
* produced. They do <strong>not</strong> support the {@code Entry.setValue}
* method. (Note however that it is possible to change mappings in the
* associated map using {@code put}.)
*
* <p>This class is a member of the
* <a href="{@docRoot}/../technotes/guides/collections/index.html">
* Java Collections Framework</a>.
*
* @param <K> the type of keys maintained by this map
* @param <V> the type of mapped values
*
* @author Josh Bloch and Doug Lea
* @see Map
* @see HashMap
* @see Hashtable
* @see Comparable
* @see Comparator
* @see Collection
* @since 1.2
*/
Fields
用于维护 Map 的 size，以及 Map 的根结点。
/**
* The comparator used to maintain order in this tree map, or
* null if it uses the natural ordering of its keys.
*
* @serial
*/
private final Comparator<? super K> comparator;
private transient Entry<K,V> root;
/**
* The number of entries in the tree
*/
private transient int size = 0;
/**
* The number of structural modifications to the tree.
*/
private transient int modCount = 0;
Constructor
构造函数，创建一个新的空集合，并组织为 key 的自然排列顺序。
/**
* Constructs a new, empty tree map, using the natural ordering of its
* keys. All keys inserted into the map must implement the {@link
* Comparable} interface. Furthermore, all such keys must be
* <em>mutually comparable</em>: {@code k1.compareTo(k2)} must not throw
* a {@code ClassCastException} for any keys {@code k1} and
* {@code k2} in the map. If the user attempts to put a key into the
* map that violates this constraint (for example, the user attempts to
* put a string key into a map whose keys are integers), the
* {@code put(Object key, Object value)} call will throw a
* {@code ClassCastException}.
*/
public TreeMap() {
comparator = null;
}
构造函数，创建新的空集合，并用 Comparator 组织 key 的排列。
/**
* Constructs a new, empty tree map, ordered according to the given
* comparator. All keys inserted into the map must be <em>mutually
* comparable</em> by the given comparator: {@code comparator.compare(k1,
* k2)} must not throw a {@code ClassCastException} for any keys
* {@code k1} and {@code k2} in the map. If the user attempts to put
* a key into the map that violates this constraint, the {@code put(Object
* key, Object value)} call will throw a
* {@code ClassCastException}.
*
* @param comparator the comparator that will be used to order this map.
* If {@code null}, the {@linkplain Comparable natural
* ordering} of the keys will be used.
*/
public TreeMap(Comparator<? super K> comparator) {
this.comparator = comparator;
}
用一个已有的 Map 构造 TreeMap，按照自然顺序来组织 key，将 Map 中的每一个元素放入 TreeMap 中。
/**
* Constructs a new tree map containing the same mappings as the given
* map, ordered according to the <em>natural ordering</em> of its keys.
* All keys inserted into the new map must implement the {@link
* Comparable} interface. Furthermore, all such keys must be
* <em>mutually comparable</em>: {@code k1.compareTo(k2)} must not throw
* a {@code ClassCastException} for any keys {@code k1} and
* {@code k2} in the map. This method runs in n*log(n) time.
*
* @param m the map whose mappings are to be placed in this map
* @throws ClassCastException if the keys in m are not {@link Comparable},
* or are not mutually comparable
* @throws NullPointerException if the specified map is null
*/
public TreeMap(Map<? extends K, ? extends V> m) {
comparator = null;
putAll(m);
}
用另一个 SortedMap 来构造 TreeMap，使用 SortedMap 的 Comparator 来组织 key 的排列，从而具有相同的 key 顺序。
/**
* Constructs a new tree map containing the same mappings and
* using the same ordering as the specified sorted map. This
* method runs in linear time.
*
* @param m the sorted map whose mappings are to be placed in this map,
* and whose comparator is to be used to sort this map
* @throws NullPointerException if the specified map is null
*/
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) {
}
}
Node
红黑树结点的定义。给定父结点、key、value 可以构造一个新结点：
- 孩子指针为
null - 结点默认颜色为黑色
// Red-black mechanics
private static final boolean RED = false;
private static final boolean BLACK = true;
/**
* Node in the Tree. Doubles as a means to pass key-value pairs back to
* user (see Map.Entry).
*/
static final class Entry<K,V> implements Map.Entry<K,V> {
K key;
V value;
Entry<K,V> left;
Entry<K,V> right;
Entry<K,V> parent;
boolean color = BLACK;
/**
* Make a new cell with given key, value, and parent, and with
* {@code null} child links, and BLACK color.
*/
Entry(K key, V value, Entry<K,V> parent) {
this.key = key;
this.value = value;
this.parent = parent;
}
/**
* Returns the key.
*
* @return the key
*/
public K getKey() {
return key;
}
/**
* Returns the value associated with the key.
*
* @return the value associated with the key
*/
public V getValue() {
return value;
}
/**
* Replaces the value currently associated with the key with the given
* value.
*
* @return the value associated with the key before this method was
* called
*/
public V setValue(V value) {
V oldValue = this.value;
this.value = value;
return oldValue;
}
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());
}
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;
}
}
Tree Operations
返回后下一个 entry：
- 首先寻找右子树的最左下结点
- 如果没有右子树，则需要回溯到 parent 结点
- 如果当前结点为 parent 的左子树，下一个 entry 应当就是 parent 的 entry
- 如果当前结点为 parent 的右子树，则需要一直向上回溯，直到该子树为某个结点的左子树为止，该结点就是下一个结点
/**
* Returns the successor of the specified Entry, or null if no such.
*/
static <K,V> TreeMap.Entry<K,V> successor(Entry<K,V> t) {
if (t == null)
return null;
else if (t.right != null) {
Entry<K,V> p = t.right;
while (p.left != null)
p = p.left;
return p;
} else {
Entry<K,V> p = t.parent;
Entry<K,V> ch = t;
while (p != null && ch == p.right) {
ch = p;
p = p.parent;
}
return p;
}
}
返回前一个 entry：
- 首先寻找左子树的最右下结点
- 如果没有左子树，则向 parent 回溯
- 如果当前结点为 parent 的右子树，那么 parent 的 entry 就是前一个 entry
- 如果当前结点为 parent 的左子树，那么需要一直回溯，直到子树成为某个结点的右子树为止，该结点就是前一个结点
/**
* Returns the predecessor of the specified Entry, or null if no such.
*/
static <K,V> Entry<K,V> predecessor(Entry<K,V> t) {
if (t == null)
return null;
else if (t.left != null) {
Entry<K,V> p = t.left;
while (p.right != null)
p = p.right;
return p;
} else {
Entry<K,V> p = t.parent;
Entry<K,V> ch = t;
while (p != null && ch == p.left) {
ch = p;
p = p.parent;
}
return p;
}
}
红黑树操作的辅助函数：
- 返回或设置颜色
- 返回左子树 / 右子树 / 父结点
/**
* Balancing operations.
*
* 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;
}
具体的红黑树操作函数：
- 左旋 / 右旋
- 插入和删除后的修复平衡性操作
不是说写得不好，只能说是没啥可读性了。
/** From CLR */
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;
}
}
/** From CLR */
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;
}
}
/** From CLR */
private void fixAfterInsertion(Entry<K,V> x) {
x.color = RED;
while (x != null && x != root && x.parent.color == RED) {
if (parentOf(x) == leftOf(parentOf(parentOf(x)))) {
Entry<K,V> y = rightOf(parentOf(parentOf(x)));
if (colorOf(y) == RED) {
setColor(parentOf(x), BLACK);
setColor(y, BLACK);
setColor(parentOf(parentOf(x)), RED);
x = parentOf(parentOf(x));
} else {
if (x == rightOf(parentOf(x))) {
x = parentOf(x);
rotateLeft(x);
}
setColor(parentOf(x), BLACK);
setColor(parentOf(parentOf(x)), RED);
rotateRight(parentOf(parentOf(x)));
}
} else {
Entry<K,V> y = leftOf(parentOf(parentOf(x)));
if (colorOf(y) == RED) {
setColor(parentOf(x), BLACK);
setColor(y, BLACK);
setColor(parentOf(parentOf(x)), RED);
x = parentOf(parentOf(x));
} else {
if (x == leftOf(parentOf(x))) {
x = parentOf(x);
rotateRight(x);
}
setColor(parentOf(x), BLACK);
setColor(parentOf(parentOf(x)), RED);
rotateLeft(parentOf(parentOf(x)));
}
}
}
root.color = BLACK;
}
/**
* Delete node p, and then rebalance the tree.
*/
private void deleteEntry(Entry<K,V> p) {
modCount++;
size--;
// If strictly internal, copy successor's element to p and then make p
// point to successor.
if (p.left != null && p.right != null) {
Entry<K,V> s = successor(p);
p.key = s.key;
p.value = s.value;
p = s;
} // p has 2 children
// Start fixup at replacement node, if it exists.
Entry<K,V> replacement = (p.left != null ? p.left : p.right);
if (replacement != null) {
// Link replacement to parent
replacement.parent = p.parent;
if (p.parent == null)
root = replacement;
else if (p == p.parent.left)
p.parent.left = replacement;
else
p.parent.right = replacement;
// Null out links so they are OK to use by fixAfterDeletion.
p.left = p.right = p.parent = null;
// Fix replacement
if (p.color == BLACK)
fixAfterDeletion(replacement);
} else if (p.parent == null) { // return if we are the only node.
root = null;
} else { // No children. Use self as phantom replacement and unlink.
if (p.color == BLACK)
fixAfterDeletion(p);
if (p.parent != null) {
if (p == p.parent.left)
p.parent.left = null;
else if (p == p.parent.right)
p.parent.right = null;
p.parent = null;
}
}
}
/** From CLR */
private void fixAfterDeletion(Entry<K,V> x) {
while (x != root && colorOf(x) == BLACK) {
if (x == leftOf(parentOf(x))) {
Entry<K,V> sib = rightOf(parentOf(x));
if (colorOf(sib) == RED) {
setColor(sib, BLACK);
setColor(parentOf(x), RED);
rotateLeft(parentOf(x));
sib = rightOf(parentOf(x));
}
if (colorOf(leftOf(sib)) == BLACK &&
colorOf(rightOf(sib)) == BLACK) {
setColor(sib, RED);
x = parentOf(x);
} else {
if (colorOf(rightOf(sib)) == BLACK) {
setColor(leftOf(sib), BLACK);
setColor(sib, RED);
rotateRight(sib);
sib = rightOf(parentOf(x));
}
setColor(sib, colorOf(parentOf(x)));
setColor(parentOf(x), BLACK);
setColor(rightOf(sib), BLACK);
rotateLeft(parentOf(x));
x = root;
}
} else { // symmetric
Entry<K,V> sib = leftOf(parentOf(x));
if (colorOf(sib) == RED) {
setColor(sib, BLACK);
setColor(parentOf(x), RED);
rotateRight(parentOf(x));
sib = leftOf(parentOf(x));
}
if (colorOf(rightOf(sib)) == BLACK &&
colorOf(leftOf(sib)) == BLACK) {
setColor(sib, RED);
x = parentOf(x);
} else {
if (colorOf(leftOf(sib)) == BLACK) {
setColor(rightOf(sib), BLACK);
setColor(sib, RED);
rotateLeft(sib);
sib = leftOf(parentOf(x));
}
setColor(sib, colorOf(parentOf(x)));
setColor(parentOf(x), BLACK);
setColor(leftOf(sib), BLACK);
rotateRight(parentOf(x));
x = root;
}
}
}
setColor(x, BLACK);
}
这是一个递归函数，lo 和 hi 分别表示该树的第一个元素和最后一个元素。分别构造左右子树，并设置子树与父结点之间的引用关系，返回中间结点。递归结束后，函数最终返回 root 结点。
关于红黑树的具体细节不想看了... 😣
/**
* 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;
}
查找 Map 中是否存在某个 key，以及，取得某个 key 对应的 value。这两个操作都需要从 root 结点出发进行搜索。
/**
* Returns {@code true} if this map contains a mapping for the specified
* key.
*
* @param key key whose presence in this map is to be tested
* @return {@code true} if this map contains a mapping for the
* specified 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 boolean containsKey(Object key) {
return getEntry(key) != null;
}
/**
* Returns the value to which the specified key is mapped,
* or {@code null} if this map contains no mapping for the key.
*
* <p>More formally, if this map contains a mapping from a key
* {@code k} to a value {@code v} such that {@code key} compares
* equal to {@code k} according to the map's ordering, then this
* method returns {@code v}; otherwise it returns {@code null}.
* (There can be at most one such mapping.)
*
* <p>A return value of {@code null} does not <em>necessarily</em>
* indicate that the map contains no mapping for the key; it's also
* possible that the map explicitly maps the key to {@code null}.
* The {@link #containsKey containsKey} operation may be used to
* distinguish these two cases.
*
* @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);
}
/**
* Returns this map's entry for the given key, or {@code null} if the map
* does not contain an entry for the key.
*
* @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) {
// Offload comparator-based version for sake of performance
if (comparator != null)
return getEntryUsingComparator(key);
if (key == null)
throw new NullPointerException();
@SuppressWarnings("unchecked")
Comparable<? super K> k = (Comparable<? super K>) key;
Entry<K,V> p = root;
while (p != null) {
int cmp = k.compareTo(p.key);
if (cmp < 0)
p = p.left;
else if (cmp > 0)
p = p.right;
else
return p;
}
return null;
}
根据 `Comparator` 是否为 `null`，选择调用两个版本的查找
* 自然顺序版本：使用 key 的 `compareTo()` 进行比较
* 使用 `Comparator` 比较的版本：使用 `Comparator` 的 `compare()` 进行比较
从 root 结点开始比较：
* 如果 key 比当前结点小，则进入左子树（或 `null`）
* 如果 key 比当前结点大，则进入右子树（或 `null`）
* 如果 key 相同，则找到；否则就是 `null`（不存在）
/**
* Version of getEntry using comparator. Split off from getEntry
* for performance. (This is not worth doing for most methods,
* that are less dependent on comparator performance, but is
* worthwhile here.)
*/
final Entry<K,V> getEntryUsingComparator(Object key) {
@SuppressWarnings("unchecked")
K k = (K) key;
Comparator<? super K> cpr = comparator;
if (cpr != null) {
Entry<K,V> p = root;
while (p != null) {
int cmp = cpr.compare(k, p.key);
if (cmp < 0)
p = p.left;
else if (cmp > 0)
p = p.right;
else
return p;
}
}
return null;
}
查找 Map 中是否存在某个 value。由于 Map 按 key 排序，与 value 的值半毛钱关系都没有。没办法，只能线性搜素。
/**
* Returns {@code true} if this map maps one or more keys to the
* specified value. More formally, returns {@code true} if and only if
* this map contains at least one mapping to a value {@code v} such
* that {@code (value==null ? v==null : value.equals(v))}. This
* operation will probably require time linear in the map size for
* most implementations.
*
* @param value value whose presence in this map is to be tested
* @return {@code true} if a mapping to {@code value} exists;
* {@code false} otherwise
* @since 1.2
*/
public boolean containsValue(Object value) {
for (Entry<K,V> e = getFirstEntry(); e != null; e = successor(e))
if (valEquals(value, e.value))
return true;
return false;
}
遍历至最左下和最右下结点，分别取得第一个和最后一个 entry 或 key。
/**
* @throws NoSuchElementException {@inheritDoc}
*/
public K firstKey() {
return key(getFirstEntry());
}
/**
* @throws NoSuchElementException {@inheritDoc}
*/
public K lastKey() {
return key(getLastEntry());
}
/**
* 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;
}
/**
* Returns the first Entry in the TreeMap (according to the TreeMap's
* key-sort function). Returns null if the TreeMap is empty.
*/
final Entry<K,V> getFirstEntry() {
Entry<K,V> p = root;
if (p != null)
while (p.left != null)
p = p.left;
return p;
}
/**
* Returns the last Entry in the TreeMap (according to the TreeMap's
* key-sort function). Returns null if the TreeMap is empty.
*/
final Entry<K,V> getLastEntry() {
Entry<K,V> p = root;
if (p != null)
while (p.right != null)
p = p.right;
return p;
}
将指定的 Map 中的所有元素拷贝到现在的 Map 中，并替换 Map 中已经出现的 entry。其中，对 Comparator 相同的 SortedMap 进行了特殊处理。
？为啥呢
/**
* Copies all of the mappings from the specified map to this map.
* These mappings replace any mappings that this map had for any
* of the keys currently in the specified map.
*
* @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);
}
插入操作
- 首先定位到 root 结点，如果 root 结点为空，那么直接建立新结点作为 root 并返回
null - 根据
Comparator是否为null，进行两种不同版本的比较；用各自的比较函数进行比较，进入左右子树- 如果已经找到对应的 key，则用
setValue()将原值替换 - 如果因为
null而停止- 建立新的结点，并根据停止条件，插入为 parent 结点的左子树或右子树
- 调
fixAfterInsertion()红黑树合法性调整
- 如果已经找到对应的 key，则用
/**
* Associates the specified value with the specified key in this map.
* If the map previously contained a mapping for the key, the old
* value is replaced.
*
* @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); // type (and possibly null) check
root = new Entry<>(key, value, null);
size = 1;
modCount++;
return null;
}
int cmp;
Entry<K,V> parent;
// split comparator and comparable paths
Comparator<? super K> cpr = comparator;
if (cpr != null) {
do {
parent = t;
cmp = cpr.compare(key, t.key);
if (cmp < 0)
t = t.left;
else if (cmp > 0)
t = t.right;
else
return t.setValue(value);
} while (t != null);
}
else {
if (key == null)
throw new NullPointerException();
@SuppressWarnings("unchecked")
Comparable<? super K> k = (Comparable<? super K>) key;
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);
}
Entry<K,V> e = new Entry<>(key, value, parent);
if (cmp < 0)
parent.left = e;
else
parent.right = e;
fixAfterInsertion(e);
size++;
modCount++;
return null;
}
删除操作：首先根据 key 找到对应的 entry，如果不存在该 entry，直接返回皆大欢喜；如果存在，那么用一个变量暂存 value 用于返回，然后调 deleteEntry() 删除 entry，并重新调用 fixAfterDeletion() 调整红黑树合法性。最后返回被删除的 entry 中的 value：
/**
* Removes the mapping for this key from this TreeMap if present.
*
* @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) {
Entry<K,V> p = getEntry(key);
if (p == null)
return null;
V oldValue = p.value;
deleteEntry(p);
return oldValue;
}
清空映射。
/**
* Removes all of the mappings from this map.
* The map will be empty after this call returns.
*/
public void clear() {
modCount++;
size = 0;
root = null;
}
浅拷贝一份 TreeMap：实例化一个处女状态的 TreeMap，用现有的 entry 重新构建一个 TreeMap 并返回。
/**
* 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;
}
删除第一个或最后一个 entry。首先找到第一个或最后一个 entry，调 deleteEntry() 删除，并自动调整红黑树。
/**
* @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;
}
/**
* @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;
}
返回小于给定 key 的最大 entry 及其 key。从 root 结点开始搜索：
- 如果 key 已经大于当前结点
- 需要往当前结点的右子树寻找 (尽可能接近 key 的结点)
- 如果没有右子树，该结点就是小于 key 的最大结点，返回
- 如果 key 小于当前结点
- 需要往当前结点的左子树寻找 (尽可能接近 key 的结点)
- 如果没有左子树
- 回溯，直到找到一个有左子树的祖先 (祖先肯定比 key 小，不然不会进行到当前层)
- 该祖先就是小于 key 且最大的结点，返回
- 不然就返回
null
/**
* @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));
}
/**
* Returns the entry for the greatest key less than the specified key; if
* no such entry exists (i.e., the least key in the Tree is greater than
* the specified key), returns {@code null}.
*/
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;
}
返回指定 key 的 entry，如果不存在，就返回小于 key 的最大 entry。与前一个函数的差别在于在进入左右子树时，如果 key 相等就直接返回；否则就还是寻找比 key 小的最大 entry。
/**
* @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));
}
/**
* Gets the entry corresponding to the specified key; if no such entry
* exists, returns the entry for the greatest key less than the specified
* key; if no such entry exists, returns {@code null}.
*/
final Entry<K,V> getFloorEntry(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 (cmp < 0) {
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;
}
} else
return p;
}
return null;
}
从 root 结点开始搜索：
- 若当前结点已经大于 key
- 那么就找当前结点的左子树，以便尽可能接近 key
- 如果当前结点没有左子树，那么当前结点就是大于 key 的最小结点，返回
- 若当前元素还小于 key
- 就往当前结点的右子树找，以便尽可能接近 key
- 若当前结点没有右子树了，而元素还小于 key
- 那么就要一直回溯，直到结点有右子树为止 (这个结点肯定比 key 大，因为之前 key 进入其左子树)
- 该结点就是大于 key 的最小结点，返回
/**
* @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));
}
/**
* Gets the entry for the least key greater than the specified
* key; if no such entry exists, returns the entry for the least
* key greater than the specified key; if no such entry exists
* returns {@code null}.
*/
final Entry<K,V> getHigherEntry(K key) {
Entry<K,V> p = root;
while (p != null) {
int cmp = compare(key, p.key);
if (cmp < 0) {
if (p.left != null)
p = p.left;
else
return p;
} else {
if (p.right != null) {
p = p.right;
} else {
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;
}
返回指定的 key 对应的 entry，如果不存在，则返回大于 key 的最小 entry。与前一个函数基本相同，就是多了个 key 与当前结点相同时直接返回。
/**
* @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));
}
/**
* Gets the entry corresponding to the specified key; if no such entry
* exists, returns the entry for the least key greater than the specified
* key; if no such entry exists (i.e., the greatest key in the Tree is less
* than the specified key), returns {@code null}.
*/
final Entry<K,V> getCeilingEntry(K key) {
Entry<K,V> p = root;
while (p != null) {
int cmp = compare(key, p.key);
if (cmp < 0) {
if (p.left != null)
p = p.left;
else
return p;
} else if (cmp > 0) {
if (p.right != null) {
p = p.right;
} else {
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;
}
集合视角：在内部维护这三个变量
- 懒加载，这三个变量在被请求时才会被初始化
- 这三个变量又分别在内部维护了整个集合，好像有种传说中的自引用关系... 😥
/**
* 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;
private transient KeySet<K> navigableKeySet;
private transient NavigableMap<K,V> descendingMap;
以 keySet 的维护为例。对集合的操作也会体现在 keySet 上，对 keySet 的操作也会体现在集合上；在 keySet 上的操作都使用集合的函数实现。dd 对 value 集合的维护：
/**
* 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();
}
/**dddd
* @since 1.6
*/
public NavigableSet<K> navigableKeySet() {
KeySet<K> nks = navigableKeySet;
return (nks != null) ? nks : (navigableKeySet = new KeySet<>(this));
}
static final class KeySet<E> extends AbstractSet<E> implements NavigableSet<E> {
private final NavigableMap<E, ?> m;
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();
}
public int size() { return m.size(); }
public boolean isEmpty() { return m.isEmpty(); }
public boolean contains(Object o) { return m.containsKey(o); }
public void clear() { m.clear(); }
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(); }
public Comparator<? super E> comparator() { return m.comparator(); }
public E pollFirst() {
Map.Entry<E,?> e = m.pollFirstEntry();
return (e == null) ? null : e.getKey();
}
public E pollLast() {
Map.Entry<E,?> e = m.pollLastEntry();
return (e == null) ? null : e.getKey();
}
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);
}
}
/**
* 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;
if (vs == null) {
vs = new Values();
values = vs;
}
return vs;
}
class Values extends AbstractCollection<V> {
public Iterator<V> iterator() {
return new ValueIterator(getFirstEntry());
}
public int size() {
return TreeMap.this.size();
}
public boolean contains(Object o) {
return TreeMap.this.containsValue(o);
}
public boolean remove(Object o) {
for (Entry<K,V> e = getFirstEntry(); e != null; e = successor(e)) {
if (valEquals(e.getValue(), o)) {
deleteEntry(e);
return true;
}
}
return false;
}
public void clear() {
TreeMap.this.clear();
}
public Spliterator<V> spliterator() {
return new ValueSpliterator<K,V>(TreeMap.this, null, null, 0, -1, 0);
}
}
对于 entrySet 的维护。
不知道理解得到不到位。这些类的存在，只是为了给用户一种视角：有只关心 key 的视角，有只关心 value 的视角，也有只关心 entry 的视角。而针对视角所做的操作，都由 Map 提供的函数在内部加以实现，这部分对用户透明。不过自己引用自己确实要给绕晕了...... 😫
/**
* 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());
}
class EntrySet extends AbstractSet<Map.Entry<K,V>> {
public Iterator<Map.Entry<K,V>> iterator() {
return new EntryIterator(getFirstEntry());
}
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());
return p != null && valEquals(p.getValue(), value);
}
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());
if (p != null && valEquals(p.getValue(), value)) {
deleteEntry(p);
return true;
}
return false;
}
public int size() {
return TreeMap.this.size();
}
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);
}
}
替换操作，底层由 getEntry() 支持。先找到对应的 entry，然后判断条件并替换。
@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;
}
遍历每一个 entry，并应用对应的操作。
@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();
}
}
}
Sub-Collections
取子集的函数。由于集合有序，只需要指明 边界 和 是否包含边界。子集内部维护集合本身，也是自引用，但需要额外维护 子集范围
/**
* @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);
}
从该类派生出两个实现类，分别实现正序子集和反序子集：
static final class AscendingSubMap<K,V> extends NavigableSubMap<K,V> {}static final class DescendingSubMap<K,V> extends NavigableSubMap<K,V> {}
/**
* @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;
/**
* The backing map.
*/
final TreeMap<K,V> m;
/**
* Endpoints are represented as triples (fromStart, lo,
* loInclusive) and (toEnd, hi, hiInclusive). If fromStart is
* true, then the low (absolute) bound is the start of the
* backing map, and the other values are ignored. Otherwise,
* if loInclusive is true, lo is the inclusive bound, else lo
* is the exclusive bound. Similarly for the upper bound.
*/
final K lo, hi;
final boolean fromStart, toEnd;
final boolean loInclusive, hiInclusive;
NavigableSubMap(TreeMap<K,V> m,
boolean fromStart, K lo, boolean loInclusive,
boolean toEnd, K hi, boolean hiInclusive) {
if (!fromStart && !toEnd) {
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;
}
// internal utilities
final boolean tooLow(Object key) {
if (!fromStart) {
int c = m.compare(key, lo);
if (c < 0 || (c == 0 && !loInclusive))
return true;
}
return false;
}
final boolean tooHigh(Object key) {
if (!toEnd) {
int c = m.compare(key, hi);
if (c > 0 || (c == 0 && !hiInclusive))
return true;
}
return false;
}
final boolean inRange(Object key) {
return !tooLow(key) && !tooHigh(key);
}
final boolean inClosedRange(Object key) {
return (fromStart || m.compare(key, lo) >= 0)
&& (toEnd || m.compare(hi, key) >= 0);
}
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
*/
final TreeMap.Entry<K,V> absLowest() {
TreeMap.Entry<K,V> e =
(fromStart ? m.getFirstEntry() :
(loInclusive ? m.getCeilingEntry(lo) :
m.getHigherEntry(lo)));
return (e == null || tooHigh(e.key)) ? null : e;
}
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;
}
final TreeMap.Entry<K,V> absCeiling(K key) {
if (tooLow(key))
return absLowest();
TreeMap.Entry<K,V> e = m.getCeilingEntry(key);
return (e == null || tooHigh(e.key)) ? null : e;
}
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;
}
final TreeMap.Entry<K,V> absFloor(K key) {
if (tooHigh(key))
return absHighest();
TreeMap.Entry<K,V> e = m.getFloorEntry(key);
return (e == null || tooLow(e.key)) ? null : e;
}
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;
}
/** Returns the absolute high fence for ascending traversal */
final TreeMap.Entry<K,V> absHighFence() {
return (toEnd ? null : (hiInclusive ?
m.getHigherEntry(hi) :
m.getCeilingEntry(hi)));
}
/** Return the absolute low fence for descending traversal */
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);
/** Returns ascending iterator from the perspective of this submap */
abstract Iterator<K> keyIterator();
abstract Spliterator<K> keySpliterator();
/** Returns descending iterator from the perspective of this submap */
abstract Iterator<K> descendingKeyIterator();
// public methods
public boolean isEmpty() {
return (fromStart && toEnd) ? m.isEmpty() : entrySet().isEmpty();
}
public int size() {
return (fromStart && toEnd) ? m.size() : entrySet().size();
}
public final boolean containsKey(Object key) {
return inRange(key) && m.containsKey(key);
}
public final V put(K key, V value) {
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) {
return exportEntry(subCeiling(key));
}
public final K ceilingKey(K key) {
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());
}
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;
}
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;
}
// Views
transient NavigableMap<K,V> descendingMapView;
transient EntrySetView entrySetView;
transient KeySet<K> navigableKeySetView;
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();
}
public NavigableSet<K> descendingKeySet() {
return descendingMap().navigableKeySet();
}
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);
}
// View classes
abstract class EntrySetView extends AbstractSet<Map.Entry<K,V>> {
private transient int size = -1, sizeModCount;
public int size() {
if (fromStart && toEnd)
return m.size();
if (size == -1 || sizeModCount != m.modCount) {
sizeModCount = m.modCount;
size = 0;
Iterator<?> i = iterator();
while (i.hasNext()) {
size++;
i.next();
}
}
return size;
}
public boolean isEmpty() {
TreeMap.Entry<K,V> n = absLowest();
return n == null || tooHigh(n.key);
}
public boolean contains(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<?,?> node = m.getEntry(key);
return node != null &&
valEquals(node.getValue(), entry.getValue());
}
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;
}
}
/**
* Iterators for SubMaps
*/
abstract class SubMapIterator<T> implements Iterator<T> {
TreeMap.Entry<K,V> lastReturned;
TreeMap.Entry<K,V> next;
final Object fenceKey;
int expectedModCount;
SubMapIterator(TreeMap.Entry<K,V> first,
TreeMap.Entry<K,V> fence) {
expectedModCount = m.modCount;
lastReturned = null;
next = first;
fenceKey = fence == null ? UNBOUNDED : fence.key;
}
public final boolean hasNext() {
return next != null && next.key != fenceKey;
}
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;
}
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;
}
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 = lastReturned;
m.deleteEntry(lastReturned);
lastReturned = null;
expectedModCount = m.modCount;
}
final void removeDescending() {
if (lastReturned == null)
throw new IllegalStateException();
if (m.modCount != expectedModCount)
throw new ConcurrentModificationException();
m.deleteEntry(lastReturned);
lastReturned = null;
expectedModCount = m.modCount;
}
}
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;
}
}
}
Summary
em...够复杂的人要晕了。关于集合视角也好、正反视角也好，其实都是封装。最主要的还是要把握红黑树这一核心实现思想，只需要知道内部有一颗增删改查性能都为 O(log(n)) 的 BST 即可。在这一前提下，实现所有的基本操作，也就是对 BST 进行增删改查、遍历。