package java.util;
import java.io.IOException;
import java.io.Serializable;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.function.BiConsumer;
import java.util.function.BiFunction;
import java.util.function.Consumer;
import java.util.function.Function;
/**
* 1）基于哈希表的 Map 接口实现，允许使用 null 键和 null 值。
* 2）假定哈希函数将元素均匀地分布在各个桶中，HashMap 的 get 和 put 方法提供稳定的性能。
* 3）影响 HashMap 性能的两个参数：初始容量和加载因子，当元素个数超出初始容量和加载因子乘积时，
* 将进行扩容，哈希表将具有大约两倍的桶数。默认的初始容量为 16，默认的加载因子为 0.75，当需要添加大量元素时，
* 提供合适的初始容量和加载因子可以避免频繁的 rehash 操作以提高性能。
* 4）HashMap 不是线程安全的，HashMap 视图方法返回的迭代器都是快速失败的，面对并发修改，HashMap 将抛出 ConcurrentModificationException 异常。
*/
public class HashMap<K,V> extends AbstractMap<K,V>
implements Map<K,V>, Cloneable, Serializable {
private static final long serialVersionUID = 362498820763181265L;
/**
* The default initial capacity - MUST be a power of two.
* 默认初始容量，必须是 2 的幂
*/
static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; // aka 16
/**
* The maximum capacity, used if a higher value is implicitly specified
* by either of the constructors with arguments.
* MUST be a power of two <= 1<<30.
* 最大容量，如果通过构造函数指定的初始容量大于 1<<30
*/
static final int MAXIMUM_CAPACITY = 1 << 30;
/**
* The load factor used when none specified in constructor.
* 默认的加载因子【在构造函数中未指定时使用】
*/
static final float DEFAULT_LOAD_FACTOR = 0.75f;
/**
* The bin count threshold for using a tree rather than list for a
* bin. Bins are converted to trees when adding an element to a
* bin with at least this many nodes. The value must be greater
* than 2 and should be at least 8 to mesh with assumptions in
* tree removal about conversion back to plain bins upon
* shrinkage.
* 单向链表转换为红黑树的长度阈值
*/
static final int TREEIFY_THRESHOLD = 8;
/**
* The bin count threshold for untreeifying a (split) bin during a
* resize operation. Should be less than TREEIFY_THRESHOLD, and at
* most 6 to mesh with shrinkage detection under removal.
* 红黑树转换为单向链表的阈值
*/
static final int UNTREEIFY_THRESHOLD = 6;
/**
* The smallest table capacity for which bins may be treeified.
* (Otherwise the table is resized if too many nodes in a bin.)
* Should be at least 4 * TREEIFY_THRESHOLD to avoid conflicts
* between resizing and treeification thresholds.
* 单向链表转换为红黑树时，必须达到的最小表容量【hash 桶的个数】
*/
static final int MIN_TREEIFY_CAPACITY = 64;
/**
* Basic hash bin node, used for most entries. (See below for
* TreeNode subclass, and in LinkedHashMap for its Entry subclass.)
* 单向链表节点
*/
static class Node<K,V> implements Map.Entry<K,V> {
// 节点哈希值
final int hash;
// 节点键
final K key;
// 节点值
V value;
// 下一个节点
Node<K,V> next;
Node(int hash, K key, V value, Node<K,V> next) {
this.hash = hash;
this.key = key;
this.value = value;
this.next = next;
}
public final K getKey() { return key; }
public final V getValue() { return value; }
public final String toString() { return key + "=" + value; }
public final int hashCode() {
return Objects.hashCode(key) ^ Objects.hashCode(value);
}
public final V setValue(V newValue) {
V oldValue = value;
value = newValue;
return oldValue;
}
public final boolean equals(Object o) {
if (o == this)
return true;
if (o instanceof Map.Entry) {
Map.Entry<?,?> e = (Map.Entry<?,?>)o;
if (Objects.equals(key, e.getKey()) &&
Objects.equals(value, e.getValue()))
return true;
}
return false;
}
}
/* ---------------- Static utilities -------------- */
/**
* 计算键的哈希值
*/
static final int hash(Object key) {
int h;
return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
}
/**
* Returns x‘s Class if it is of the form "class C implements
* Comparable<C>", else null.
* 如果 x 实现了 Comparable 接口，则返回其 Class 对象，否则返回 null
*/
static Class<?> comparableClassFor(Object x) {
if (x instanceof Comparable) {
Class<?> c; Type[] ts, as; ParameterizedType p;
if ((c = x.getClass()) == String.class) // bypass checks
return c;
// 获取 x 所实现接口的 Type 数组
if ((ts = c.getGenericInterfaces()) != null) {
for (Type t : ts) {
/**
* 如果 t 是一个参数化类型，并且声明此参数化类型的接口名称为 Comparable，
* 并且参数化类型的实际类型参数不为 null 并且长度为 1 并且实际类型为 c
*/
if ((t instanceof ParameterizedType) &&
((p = (ParameterizedType) t).getRawType() ==
Comparable.class) &&
(as = p.getActualTypeArguments()) != null &&
as.length == 1 && as[0] == c) // type arg is c
return c;
}
}
}
return null;
}
/**
* Returns k.compareTo(x) if x matches kc (k‘s screened comparable
* class), else 0.
*/
@SuppressWarnings({"rawtypes","unchecked"}) // for cast to Comparable
static int compareComparables(Class<?> kc, Object k, Object x) {
return (x == null || x.getClass() != kc ? 0 :
((Comparable)k).compareTo(x));
}
/**
* Returns a power of two size for the given target capacity.
* 基于目标容量计算 2 的幂
*/
static final int tableSizeFor(int cap) {
int n = cap - 1;
n |= n >>> 1;
n |= n >>> 2;
n |= n >>> 4;
n |= n >>> 8;
n |= n >>> 16;
return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
}
/* ---------------- Fields -------------- */
/**
* The table, initialized on first use, and resized as
* necessary. When allocated, length is always a power of two.
* (We also tolerate length zero in some operations to allow
* bootstrapping mechanics that are currently not needed.)
* 哈希表，在第一次使用时初始化并且按需进行扩容，当完成分配时，长度总是
* 2 的幂
*/
transient Node<K,V>[] table;
/**
* Holds cached entrySet(). Note that AbstractMap fields are used
* for keySet() and values().
*/
transient Set<Map.Entry<K,V>> entrySet;
/**
* The number of key-value mappings contained in this map.
* HashMap 中键值对的个数
*/
transient int size;
/**
* The number of times this HashMap has been structurally modified
* Structural modifications are those that change the number of mappings in
* the HashMap or otherwise modify its internal structure (e.g.,
* rehash). This field is used to make iterators on Collection-views of
* the HashMap fail-fast. (See ConcurrentModificationException).
* HashMap 被结构化修改的次数
*/
transient int modCount;
/**
* The next size value at which to resize (capacity * load factor).
* 下一次执行 rehash 操作的元素阈值
* @serial
*/
int threshold;
/**
* The load factor for the hash table.
* 哈希表的加载因子
* @serial
*/
final float loadFactor;
/* ---------------- Public operations -------------- */
/**
* Constructs an empty {@code HashMap} with the specified initial
* capacity and load factor.
* 创建初始容量为 tableSizeFor(initialCapacity)，加载因子为 loadFactor 的 HashMap 实例
*/
public HashMap(int initialCapacity, float loadFactor) {
if (initialCapacity < 0)
throw new IllegalArgumentException("Illegal initial capacity: " +
initialCapacity);
if (initialCapacity > MAXIMUM_CAPACITY)
initialCapacity = MAXIMUM_CAPACITY;
if (loadFactor <= 0 || Float.isNaN(loadFactor))
throw new IllegalArgumentException("Illegal load factor: " +
loadFactor);
this.loadFactor = loadFactor;
this.threshold = tableSizeFor(initialCapacity);
}
/**
* Constructs an empty {@code HashMap} with the specified initial
* capacity and the default load factor (0.75).
* 创建初始容量为 tableSizeFor(initialCapacity)，加载因子为 0.75 的 HashMap 实例
*/
public HashMap(int initialCapacity) {
this(initialCapacity, DEFAULT_LOAD_FACTOR);
}
/**
* Constructs an empty {@code HashMap} with the default initial capacity
* (16) and the default load factor (0.75).
* 创建初始容量为 16，加载因子为 loadFactor 的 HashMap 实例
*/
public HashMap() {
this.loadFactor = DEFAULT_LOAD_FACTOR; // all other fields defaulted
}
/**
* Constructs a new {@code HashMap} with the same mappings as the
* specified {@code Map}. The {@code HashMap} is created with
* default load factor (0.75) and an initial capacity sufficient to
* hold the mappings in the specified {@code Map}.
* 基于形参 m 创建加载因子为 0.75 的 HashMap 实例
*/
public HashMap(Map<? extends K, ? extends V> m) {
this.loadFactor = DEFAULT_LOAD_FACTOR;
putMapEntries(m, false);
}
/**
* Implements Map.putAll and Map constructor.
*
* @param evict 初始化构造 HashMap 时为 false，插入元素后为 true。
*/
final void putMapEntries(Map<? extends K, ? extends V> m, boolean evict) {
int s = m.size();
if (s > 0) {
if (table == null) { // pre-size
float ft = ((float)s / loadFactor) + 1.0F;
int t = ((ft < (float)MAXIMUM_CAPACITY) ?
(int)ft : MAXIMUM_CAPACITY);
if (t > threshold)
threshold = tableSizeFor(t);
}
else if (s > threshold)
resize();
for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) {
K key = e.getKey();
V value = e.getValue();
putVal(hash(key), key, value, false, evict);
}
}
}
/**
* Returns the number of key-value mappings in this map.
* 返回哈希表中键值对的数目
*/
public int size() {
return size;
}
/**
* Returns {@code true} if this map contains no key-value mappings.
* 哈希表是否为空
*/
public boolean isEmpty() {
return size == 0;
}
/**
* 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==null ? k==null :
* key.equals(k))}, 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 <i>necessarily</i>
* 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.
* 根据指定的键，获取对应的值，键不存在或键映射的值为 null 时，返回 null，否则返回具体的值
* @see #put(Object, Object)
*/
public V get(Object key) {
Node<K,V> e;
return (e = getNode(hash(key), key)) == null ? null : e.value;
}
/**
* Implements Map.get and related methods.
* 根据哈希值和 key 获取节点
*/
final Node<K,V> getNode(int hash, Object key) {
Node<K,V>[] tab; Node<K,V> first, e; int n; K k;
// 哈希表不为 null，哈希表的长度 > 0，目标哈希值映射到的 bucket 不为 null。
if ((tab = table) != null && (n = tab.length) > 0 &&
(first = tab[(n - 1) & hash]) != null) {
/**
* 第一个节点的哈希值和目标哈希值相等，并且节点的键和目标键引用相等或
* 目标键不为 null 并且节点键和目标键 equals 相等【第一个节点即为目标节点】。
*/
if (first.hash == hash && // always check first node
((k = first.key) == key || (key != null && key.equals(k))))
return first;
// 获取第二个节点
if ((e = first.next) != null) {
// 如果是一颗红黑树，则执行树节点的获取操作
if (first instanceof TreeNode)
return ((TreeNode<K,V>)first).getTreeNode(hash, key);
do {
// 递归遍历单链表的所有节点
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
return e;
} while ((e = e.next) != null);
}
}
return null;
}
/**
* Returns {@code true} if this map contains a mapping for the
* specified key.
* HashMap 是否包含指定的键
*/
public boolean containsKey(Object key) {
return getNode(hash(key), key) != null;
}
/**
* 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.
* 往 HashMap 中插入新的键值对，如果键已经存在，则替换旧值
*/
public V put(K key, V value) {
return putVal(hash(key), key, value, false, true);
}
/**
* Implements Map.put and related methods.
*
* @param hash hash for key【键的哈希值】
* @param key the key【键对象】
* @param value the value to put【映射的值】
* @param onlyIfAbsent if true, don‘t change existing value【如果为 true，则不覆盖已经存在的值】
* @param evict if false, the table is in creation mode.【如果为 false，则哈希表在创建模式】
* @return previous value, or null if none
*/
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
boolean evict) {
Node<K,V>[] tab; Node<K,V> p; int n, i;
// 如果 table 为 null，或长度为 0，则执行扩容操作
if ((tab = table) == null || (n = tab.length) == 0)
n = (tab = resize()).length;
// 哈希值映射的 bucket 为 null，则创建新的单链表节点
if ((p = tab[i = (n - 1) & hash]) == null)
tab[i] = newNode(hash, key, value, null);
else {
Node<K,V> e; K k;
/**
* 第一个节点的哈希值和目标哈希值相等，节点的键和目标键引用相等或 equals 相等，
* 第一个节点就是目标节点。
*/
if (p.hash == hash &&
((k = p.key) == key || (key != null && key.equals(k))))
e = p;
// 如果节点是红黑树
else if (p instanceof TreeNode)
e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
else {
// 统计单链表元素个数
for (int binCount = 0; ; ++binCount) {
// 当前节点的 next 为 null，则创建单链表节点
if ((e = p.next) == null) {
p.next = newNode(hash, key, value, null);
// 如果单链表节点的个数大于 8，则尝试树化
if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
treeifyBin(tab, hash);
break;
}
// 如果找到目标节点，则直接退出循环
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
break;
// 更新迭代节点
p = e;
}
}
if (e != null) { // existing mapping for key【键已经存在映射】
V oldValue = e.value;
// 允许覆盖旧值或旧值为 null，则更新为新值
if (!onlyIfAbsent || oldValue == null)
e.value = value;
// LinkedHashMap 的钩子函数
afterNodeAccess(e);
// 返回旧值
return oldValue;
}
}
++modCount;
// 自增 size 值之后如果超出哈希表扩容阈值，则执行扩容操作
if (++size > threshold)
resize();
afterNodeInsertion(evict);
return null;
}
/**
* Initializes or doubles table size. If null, allocates in
* accord with initial capacity target held in field threshold.
* Otherwise, because we are using power-of-two expansion, the
* elements from each bin must either stay at same index, or move
* with a power of two offset in the new table.
*
* @return the table
*/
final Node<K,V>[] resize() {
Node<K,V>[] oldTab = table;
// 获取旧 table 的长度
int oldCap = (oldTab == null) ? 0 : oldTab.length;
// 获取旧的扩容阈值
int oldThr = threshold;
int newCap, newThr = 0;
if (oldCap > 0) {
/**
* 旧 table 的长度大于等于 1<<30，则扩容阈值设置为 Integer.MAX_VALUE，并直接返回，
* table 的容量不再发生变化。
*/
if (oldCap >= MAXIMUM_CAPACITY) {
threshold = Integer.MAX_VALUE;
return oldTab;
}
// 基于旧 table 容量执行双倍扩容，并且新的容量小于 1<<30 并且旧容量 >= 16
else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&
oldCap >= DEFAULT_INITIAL_CAPACITY)
// 扩容阈值扩大为原来的两倍
newThr = oldThr << 1; // double threshold
}
// oldCap <= 0 && oldThr > 0 第一次新增元素
else if (oldThr > 0) // initial capacity was placed in threshold
// 构造函数指定了初始化容量
newCap = oldThr;
else { // zero initial threshold signifies using defaults
/**
* oldCap <=0 && oldThr <=0
*/
newCap = DEFAULT_INITIAL_CAPACITY;
newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);
}
// 新的扩容阈值为 0，则重新计算扩容阈值
if (newThr == 0) {
float ft = (float)newCap * loadFactor;
newThr = (newCap < MAXIMUM_CAPACITY && ft < (float)MAXIMUM_CAPACITY ?
(int)ft : Integer.MAX_VALUE);
}
threshold = newThr;
@SuppressWarnings({"rawtypes","unchecked"})
// 基于新的容量创建 table
Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];
table = newTab;
// 旧 table 不为 null，则需要执行数据迁移
if (oldTab != null) {
for (int j = 0; j < oldCap; ++j) {
Node<K,V> e;
// table 上的 bucket 有元素
if ((e = oldTab[j]) != null) {
oldTab[j] = null;
// 如果只有单个节点，则将其直接 rehash 到新的 bucket 上
if (e.next == null)
newTab[e.hash & (newCap - 1)] = e;
// 如果是一个红黑树
else if (e instanceof TreeNode)
((TreeNode<K,V>)e).split(this, newTab, j, oldCap);
else { // preserve order
// 如果是一个单向链表
Node<K,V> loHead = null, loTail = null;
Node<K,V> hiHead = null, hiTail = null;
Node<K,V> next;
do {
// 获取第二个节点
next = e.next;
/**
* 键的哈希值 < oldCap，则 bucket 的索引保持不变
*/
if ((e.hash & oldCap) == 0) {
// 迁移第一个元素，则将 e 设置为 loHead
if (loTail == null)
// 更新头节点
loHead = e;
else
// 更新尾节点的后置节点为 e
loTail.next = e;
// 新的尾节点为 e
loTail = e;
}
else {
/**
* 键的哈希值 > oldCap，则 bucket 的索引更新为【原索引+oldCap】
*/
if (hiTail == null)
hiHead = e;
else
hiTail.next = e;
hiTail = e;
}
// 遍历处理单向链表的每个节点
} while ((e = next) != null);
// 将哈希值 < oldCap 的单向链表赋值到 bucket 上
if (loTail != null) {
loTail.next = null;
newTab[j] = loHead;
}
// 将哈希值 > oldCap 的单向链表赋值到 bucket+oldCap 上
if (hiTail != null) {
hiTail.next = null;
newTab[j + oldCap] = hiHead;
}
}
}
}
}
// 扩容完毕返回新的 table
return newTab;
}
/**
* Replaces all linked nodes in bin at index for given hash unless
* table is too small, in which case resizes instead.
*/
final void treeifyBin(Node<K,V>[] tab, int hash) {
int n, index; Node<K,V> e;
/**
* 哈希表为 null，或 table 的长度小于 64，则执行 table 的扩容
*/
if (tab == null || (n = tab.length) < MIN_TREEIFY_CAPACITY)
resize();
// 否则执行单向链表的树化
else if ((e = tab[index = (n - 1) & hash]) != null) {
TreeNode<K,V> hd = null, tl = null;
do {
/**
* 将单向链表中的所有节点都转换为树节点，并保持单向链表结构，
* 兼容 Jdk1.7 及以前的 HashMap，方便查找和消费
*/
TreeNode<K,V> p = replacementTreeNode(e, null);
if (tl == null)
// 设置第一个树节点
hd = p;
else {
p.prev = tl;
tl.next = p;
}
tl = p;
} while ((e = e.next) != null);
if ((tab[index] = hd) != null)
// 执行红黑树化操作
hd.treeify(tab);
}
}
/**
* Copies all of the mappings from the specified map to this map.
* These mappings will replace any mappings that this map had for
* any of the keys currently in the specified map.
*/
public void putAll(Map<? extends K, ? extends V> m) {
putMapEntries(m, true);
}
/**
* Removes the mapping for the specified key from this map if present.
* 移除目标键，并返回其值，如果节点不存在，则返回 null
*/
public V remove(Object key) {
Node<K,V> e;
return (e = removeNode(hash(key), key, null, false, true)) == null ?
null : e.value;
}
/**
* Implements Map.remove and related methods.
*
* @param hash hash for key【键的哈希值】
* @param key the key【键对象】
* @param value the value to match if matchValue, else ignored【值对象】
* @param matchValue if true only remove if value is equal【为 true 时，只有当值相等时才移除】
* @param movable if false do not move other nodes while removing【为 false 时，不移除其他的节点】
* @return the node, or null if none
*/
final Node<K,V> removeNode(int hash, Object key, Object value,
boolean matchValue, boolean movable) {
Node<K,V>[] tab; Node<K,V> p; int n, index;
if ((tab = table) != null && (n = tab.length) > 0 &&
(p = tab[index = (n - 1) & hash]) != null) {
// 基于目标哈希值能找到 bucket
Node<K,V> node = null, e; K k; V v;
if (p.hash == hash &&
((k = p.key) == key || (key != null && key.equals(k))))
node = p;
else if ((e = p.next) != null) {
if (p instanceof TreeNode)
node = ((TreeNode<K,V>)p).getTreeNode(hash, key);
else {
do {
if (e.hash == hash &&
((k = e.key) == key ||
(key != null && key.equals(k)))) {
node = e;
break;
}
p = e;
} while ((e = e.next) != null);
}
}
// 如果目标节点存在
if (node != null && (!matchValue || (v = node.value) == value ||
(value != null && value.equals(v)))) {
if (node instanceof TreeNode)
((TreeNode<K,V>)node).removeTreeNode(this, tab, movable);
// 如果是单向链表第一个节点
else if (node == p)
tab[index] = node.next;
else
// 如果是单向链表中间节点
p.next = node.next;
++modCount;
--size;
afterNodeRemoval(node);
return node;
}
}
return null;
}
/**
* Removes all of the mappings from this map.
* The map will be empty after this call returns.
*/
public void clear() {
Node<K,V>[] tab;
modCount++;
/**
* 将所有的 bucket 都置为 null
*/
if ((tab = table) != null && size > 0) {
size = 0;
for (int i = 0; i < tab.length; ++i)
tab[i] = null;
}
}
/**
* Returns {@code true} if this map maps one or more keys to the
* specified value.
* HashMap 包含指定的值
*/
public boolean containsValue(Object value) {
Node<K,V>[] tab; V v;
if ((tab = table) != null && size > 0) {
for (Node<K,V> e : tab) {
for (; e != null; e = e.next) {
if ((v = e.value) == value ||
(value != null && value.equals(v)))
return true;
}
}
}
return false;
}
/**
* Returns a {@link Set} view of the keys contained in this map.
* 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.
* 返回 HashMap 键集合
*/
public Set<K> keySet() {
Set<K> ks = keySet;
if (ks == null) {
ks = new KeySet();
keySet = ks;
}
return ks;
}
final class KeySet extends AbstractSet<K> {
public final int size() { return size; }
public final void clear() { HashMap.this.clear(); }
public final Iterator<K> iterator() { return new KeyIterator(); }
public final boolean contains(Object o) { return containsKey(o); }
public final boolean remove(Object key) {
return removeNode(hash(key), key, null, false, true) != null;
}
public final Spliterator<K> spliterator() {
return new KeySpliterator<>(HashMap.this, 0, -1, 0, 0);
}
public final void forEach(Consumer<? super K> action) {
Node<K,V>[] tab;
if (action == null)
throw new NullPointerException();
if (size > 0 && (tab = table) != null) {
int mc = modCount;
for (Node<K,V> e : tab) {
for (; e != null; e = e.next)
action.accept(e.key);
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
}
/**
* Returns a {@link Collection} view of the values contained in this map.
* 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.
*
* @return a view of the values contained in this map
*/
public Collection<V> values() {
Collection<V> vs = values;
if (vs == null) {
vs = new Values();
values = vs;
}
return vs;
}
final class Values extends AbstractCollection<V> {
public final int size() { return size; }
public final void clear() { HashMap.this.clear(); }
public final Iterator<V> iterator() { return new ValueIterator(); }
public final boolean contains(Object o) { return containsValue(o); }
public final Spliterator<V> spliterator() {
return new ValueSpliterator<>(HashMap.this, 0, -1, 0, 0);
}
public final void forEach(Consumer<? super V> action) {
Node<K,V>[] tab;
if (action == null)
throw new NullPointerException();
if (size > 0 && (tab = table) != null) {
int mc = modCount;
for (Node<K,V> e : tab) {
for (; e != null; e = e.next)
action.accept(e.value);
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
}
/**
* Returns a {@link Set} view of the mappings contained in this map.
* 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.
*
* @return a set view of the mappings contained in this map
*/
public Set<Map.Entry<K,V>> entrySet() {
Set<Map.Entry<K,V>> es;
return (es = entrySet) == null ? (entrySet = new EntrySet()) : es;
}
final class EntrySet extends AbstractSet<Map.Entry<K,V>> {
public final int size() { return size; }
public final void clear() { HashMap.this.clear(); }
public final Iterator<Map.Entry<K,V>> iterator() {
return new EntryIterator();
}
public final boolean contains(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry<?,?> e = (Map.Entry<?,?>) o;
Object key = e.getKey();
Node<K,V> candidate = getNode(hash(key), key);
return candidate != null && candidate.equals(e);
}
public final boolean remove(Object o) {
if (o instanceof Map.Entry) {
Map.Entry<?,?> e = (Map.Entry<?,?>) o;
Object key = e.getKey();
Object value = e.getValue();
return removeNode(hash(key), key, value, true, true) != null;
}
return false;
}
public final Spliterator<Map.Entry<K,V>> spliterator() {
return new EntrySpliterator<>(HashMap.this, 0, -1, 0, 0);
}
public final void forEach(Consumer<? super Map.Entry<K,V>> action) {
Node<K,V>[] tab;
if (action == null)
throw new NullPointerException();
if (size > 0 && (tab = table) != null) {
int mc = modCount;
for (Node<K,V> e : tab) {
for (; e != null; e = e.next)
action.accept(e);
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
}
// Overrides of JDK8 Map extension methods
/**
* 如果键不存在，则返回默认值
*/
@Override
public V getOrDefault(Object key, V defaultValue) {
Node<K,V> e;
return (e = getNode(hash(key), key)) == null ? defaultValue : e.value;
}
/**
* 只有当键不存在时，才新增键值对
* created by ZXD at 15 Jul 2018 T 16:53:45
*/
@Override
public V putIfAbsent(K key, V value) {
return putVal(hash(key), key, value, true, true);
}
/**
* 只有当键和值都匹配时，才移除节点
* created by ZXD at 15 Jul 2018 T 16:54:04
*/
@Override
public boolean remove(Object key, Object value) {
return removeNode(hash(key), key, value, true, true) != null;
}
/**
* 如果键和旧值都匹配，则更新新值，类似于 CAS 操作
* created by ZXD at 15 Jul 2018 T 16:54:29
*/
@Override
public boolean replace(K key, V oldValue, V newValue) {
Node<K,V> e; V v;
if ((e = getNode(hash(key), key)) != null &&
((v = e.value) == oldValue || (v != null && v.equals(oldValue)))) {
e.value = newValue;
afterNodeAccess(e);
return true;
}
return false;
}
/**
* 如果键已经存在，则使用新值替换旧值，并返回旧值
* created by ZXD at 15 Jul 2018 T 16:55:12
*/
@Override
public V replace(K key, V value) {
Node<K,V> e;
if ((e = getNode(hash(key), key)) != null) {
V oldValue = e.value;
e.value = value;
afterNodeAccess(e);
return oldValue;
}
return null;
}
/**
* 1）如果旧的键和值都不为 null，则直接返回旧值。
* 2）基于函数式接口和键计算新值，如果为 null，则直接返回 null
* 3）如果旧节点存在，旧值为 null，则将其更新为计算值
*
*
*/
@Override
public V computeIfAbsent(K key,
Function<? super K, ? extends V> mappingFunction) {
if (mappingFunction == null)
throw new NullPointerException();
int hash = hash(key);
Node<K,V>[] tab; Node<K,V> first; int n, i;
int binCount = 0;
TreeNode<K,V> t = null;
Node<K,V> old = null;
if (size > threshold || (tab = table) == null ||
(n = tab.length) == 0)
n = (tab = resize()).length;
if ((first = tab[i = (n - 1) & hash]) != null) {
if (first instanceof TreeNode)
old = (t = (TreeNode<K,V>)first).getTreeNode(hash, key);
else {
Node<K,V> e = first; K k;
do {
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k)))) {
old = e;
break;
}
++binCount;
} while ((e = e.next) != null);
}
V oldValue;
// 旧节点存在，并且其值不为 null，则直接返回旧值
if (old != null && (oldValue = old.value) != null) {
afterNodeAccess(old);
return oldValue;
}
}
int mc = modCount;
if (mc != modCount) { throw new ConcurrentModificationException(); }
// 基于函数式接口和键计算新值
V v = mappingFunction.apply(key);
// 新值为 null，则直接返回 null
if (v == null) {
return null;
// 旧节点不为 null，但是其值为 null，则更新值
} else if (old != null) {
old.value = v;
afterNodeAccess(old);
return v;
}
// 旧节点不存在
else if (t != null)
// 如果 bucket 为红黑树，则新增树节点
t.putTreeVal(this, tab, hash, key, v);
else {
// 否则在单向链表的头部新增节点
tab[i] = newNode(hash, key, v, first);
if (binCount >= TREEIFY_THRESHOLD - 1)
// 单向链表的长度 > 8，则尝试执行树化操作
treeifyBin(tab, hash);
}
modCount = mc + 1;
++size;
afterNodeInsertion(true);
return v;
}
@Override
public V computeIfPresent(K key,
BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
if (remappingFunction == null)
throw new NullPointerException();
Node<K,V> e; V oldValue;
int hash = hash(key);
// 指定的键存在，并且其值不为 null
if ((e = getNode(hash, key)) != null &&
(oldValue = e.value) != null) {
int mc = modCount;
/**
* 将键和旧值传递给函数式接口计算出新值，如果值不为 null，则更新旧值；
* 否则删除该键值对。
*/
V v = remappingFunction.apply(key, oldValue);
if (mc != modCount) { throw new ConcurrentModificationException(); }
if (v != null) {
e.value = v;
afterNodeAccess(e);
return v;
}
else
removeNode(hash, key, null, false, true);
}
return null;
}
@Override
public V compute(K key,
BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
if (remappingFunction == null)
throw new NullPointerException();
int hash = hash(key);
Node<K,V>[] tab; Node<K,V> first; int n, i;
int binCount = 0;
TreeNode<K,V> t = null;
Node<K,V> old = null;
if (size > threshold || (tab = table) == null ||
(n = tab.length) == 0)
n = (tab = resize()).length;
if ((first = tab[i = (n - 1) & hash]) != null) {
if (first instanceof TreeNode)
old = (t = (TreeNode<K,V>)first).getTreeNode(hash, key);
else {
Node<K,V> e = first; K k;
do {
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k)))) {
old = e;
break;
}
++binCount;
} while ((e = e.next) != null);
}
}
V oldValue = (old == null) ? null : old.value;
int mc = modCount;
// 将旧键和旧值传递给函数式接口计算新值
V v = remappingFunction.apply(key, oldValue);
if (mc != modCount) { throw new ConcurrentModificationException(); }
// 如果旧键存在
if (old != null) {
// 新的计算值不为 null，则更新旧值
if (v != null) {
old.value = v;
afterNodeAccess(old);
}
// 新的计算值为 null，则删除该键值对
else
removeNode(hash, key, null, false, true);
}
// 旧键不存在，新的计算值不为 null
else if (v != null) {
if (t != null)
// 插入新的树节点
t.putTreeVal(this, tab, hash, key, v);
else {
// 在单向链表头部插入新节点
tab[i] = newNode(hash, key, v, first);
if (binCount >= TREEIFY_THRESHOLD - 1)
treeifyBin(tab, hash);
}
modCount = mc + 1;
++size;
afterNodeInsertion(true);
}
return v;
}
@Override
public V merge(K key, V value,
BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
if (value == null)
throw new NullPointerException();
if (remappingFunction == null)
throw new NullPointerException();
int hash = hash(key);
Node<K,V>[] tab; Node<K,V> first; int n, i;
int binCount = 0;
TreeNode<K,V> t = null;
Node<K,V> old = null;
if (size > threshold || (tab = table) == null ||
(n = tab.length) == 0)
n = (tab = resize()).length;
if ((first = tab[i = (n - 1) & hash]) != null) {
if (first instanceof TreeNode)
old = (t = (TreeNode<K,V>)first).getTreeNode(hash, key);
else {
Node<K,V> e = first; K k;
do {
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k)))) {
old = e;
break;
}
++binCount;
} while ((e = e.next) != null);
}
}
// 旧节点存在
if (old != null) {
V v;
// 旧值不为 null
if (old.value != null) {
int mc = modCount;
// 将旧值和目标值传递给函数式接口，计算新值
v = remappingFunction.apply(old.value, value);
if (mc != modCount) {
throw new ConcurrentModificationException();
}
} else {
// 新值即为目标值
v = value;
}
// 新值不为 null，则更新旧值
if (v != null) {
old.value = v;
afterNodeAccess(old);
}
// 新值为 null，则删除节点
else
removeNode(hash, key, null, false, true);
return v;
}
// 节点不存在，目标值不为 null
if (value != null) {
if (t != null)
// 插入树节点
t.putTreeVal(this, tab, hash, key, value);
else {
// 插入到单向链表头部
tab[i] = newNode(hash, key, value, first);
if (binCount >= TREEIFY_THRESHOLD - 1)
treeifyBin(tab, hash);
}
++modCount;
++size;
afterNodeInsertion(true);
}
return value;
}
/**
* 将 key 和 value 传递给函数式接口进行消费
*/
@Override
public void forEach(BiConsumer<? super K, ? super V> action) {
Node<K,V>[] tab;
if (action == null)
throw new NullPointerException();
if (size > 0 && (tab = table) != null) {
int mc = modCount;
for (Node<K,V> e : tab) {
for (; e != null; e = e.next)
action.accept(e.key, e.value);
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
/**
* 将旧的 key 和 value 传递给函数式接口计算新值，并替换旧值
* created by ZXD at 15 Jul 2018 T 17:16:20
*/
@Override
public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
Node<K,V>[] tab;
if (function == null)
throw new NullPointerException();
if (size > 0 && (tab = table) != null) {
int mc = modCount;
for (Node<K,V> e : tab) {
for (; e != null; e = e.next) {
e.value = function.apply(e.key, e.value);
}
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
/* ------------------------------------------------------------ */
// Cloning and serialization
/**
* Returns a shallow copy of this {@code HashMap} instance: the keys and
* values themselves are not cloned.
*/
@SuppressWarnings("unchecked")
@Override
public Object clone() {
HashMap<K,V> result;
try {
result = (HashMap<K,V>)super.clone();
} catch (CloneNotSupportedException e) {
// this shouldn‘t happen, since we are Cloneable
throw new InternalError(e);
}
result.reinitialize();
result.putMapEntries(this, false);
return result;
}
// These methods are also used when serializing HashSets
final float loadFactor() { return loadFactor; }
final int capacity() {
return (table != null) ? table.length :
(threshold > 0) ? threshold :
DEFAULT_INITIAL_CAPACITY;
}
/* ------------------------------------------------------------ */
// iterators
abstract class HashIterator {
Node<K,V> next; // next entry to return
Node<K,V> current; // current entry
int expectedModCount; // for fast-fail
int index; // current slot
HashIterator() {
expectedModCount = modCount;
Node<K,V>[] t = table;
current = next = null;
index = 0;
if (t != null && size > 0) { // advance to first entry
do {} while (index < t.length && (next = t[index++]) == null);
}
}
public final boolean hasNext() {
return next != null;
}
final Node<K,V> nextNode() {
Node<K,V>[] t;
Node<K,V> e = next;
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
if (e == null)
throw new NoSuchElementException();
if ((next = (current = e).next) == null && (t = table) != null) {
do {} while (index < t.length && (next = t[index++]) == null);
}
return e;
}
public final void remove() {
Node<K,V> p = current;
if (p == null)
throw new IllegalStateException();
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
current = null;
removeNode(p.hash, p.key, null, false, false);
expectedModCount = modCount;
}
}
final class KeyIterator extends HashIterator
implements Iterator<K> {
public final K next() { return nextNode().key; }
}
final class ValueIterator extends HashIterator
implements Iterator<V> {
public final V next() { return nextNode().value; }
}
final class EntryIterator extends HashIterator
implements Iterator<Map.Entry<K,V>> {
public final Map.Entry<K,V> next() { return nextNode(); }
}
/* ------------------------------------------------------------ */
// spliterators
static class HashMapSpliterator<K,V> {
final HashMap<K,V> map;
Node<K,V> current; // current node
int index; // current index, modified on advance/split
int fence; // one past last index
int est; // size estimate
int expectedModCount; // for comodification checks
HashMapSpliterator(HashMap<K,V> m, int origin,
int fence, int est,
int expectedModCount) {
this.map = m;
this.index = origin;
this.fence = fence;
this.est = est;
this.expectedModCount = expectedModCount;
}
final int getFence() { // initialize fence and size on first use
int hi;
if ((hi = fence) < 0) {
HashMap<K,V> m = map;
est = m.size;
expectedModCount = m.modCount;
Node<K,V>[] tab = m.table;
hi = fence = (tab == null) ? 0 : tab.length;
}
return hi;
}
public final long estimateSize() {
getFence(); // force init
return (long) est;
}
}
static final class KeySpliterator<K,V>
extends HashMapSpliterator<K,V>
implements Spliterator<K> {
KeySpliterator(HashMap<K,V> m, int origin, int fence, int est,
int expectedModCount) {
super(m, origin, fence, est, expectedModCount);
}
public KeySpliterator<K,V> trySplit() {
int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
return (lo >= mid || current != null) ? null :
new KeySpliterator<>(map, lo, index = mid, est >>>= 1,
expectedModCount);
}
public void forEachRemaining(Consumer<? super K> action) {
int i, hi, mc;
if (action == null)
throw new NullPointerException();
HashMap<K,V> m = map;
Node<K,V>[] tab = m.table;
if ((hi = fence) < 0) {
mc = expectedModCount = m.modCount;
hi = fence = (tab == null) ? 0 : tab.length;
}
else
mc = expectedModCount;
if (tab != null && tab.length >= hi &&
(i = index) >= 0 && (i < (index = hi) || current != null)) {
Node<K,V> p = current;
current = null;
do {
if (p == null)
p = tab[i++];
else {
action.accept(p.key);
p = p.next;
}
} while (p != null || i < hi);
if (m.modCount != mc)
throw new ConcurrentModificationException();
}
}
public boolean tryAdvance(Consumer<? super K> action) {
int hi;
if (action == null)
throw new NullPointerException();
Node<K,V>[] tab = map.table;
if (tab != null && tab.length >= (hi = getFence()) && index >= 0) {
while (current != null || index < hi) {
if (current == null)
current = tab[index++];
else {
K k = current.key;
current = current.next;
action.accept(k);
if (map.modCount != expectedModCount)
throw new ConcurrentModificationException();
return true;
}
}
}
return false;
}
public int characteristics() {
return (fence < 0 || est == map.size ? Spliterator.SIZED : 0) |
Spliterator.DISTINCT;
}
}
static final class ValueSpliterator<K,V>
extends HashMapSpliterator<K,V>
implements Spliterator<V> {
ValueSpliterator(HashMap<K,V> m, int origin, int fence, int est,
int expectedModCount) {
super(m, origin, fence, est, expectedModCount);
}
public ValueSpliterator<K,V> trySplit() {
int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
return (lo >= mid || current != null) ? null :
new ValueSpliterator<>(map, lo, index = mid, est >>>= 1,
expectedModCount);
}
public void forEachRemaining(Consumer<? super V> action) {
int i, hi, mc;
if (action == null)
throw new NullPointerException();
HashMap<K,V> m = map;
Node<K,V>[] tab = m.table;
if ((hi = fence) < 0) {
mc = expectedModCount = m.modCount;
hi = fence = (tab == null) ? 0 : tab.length;
}
else
mc = expectedModCount;
if (tab != null && tab.length >= hi &&
(i = index) >= 0 && (i < (index = hi) || current != null)) {
Node<K,V> p = current;
current = null;
do {
if (p == null)
p = tab[i++];
else {
action.accept(p.value);
p = p.next;
}
} while (p != null || i < hi);
if (m.modCount != mc)
throw new ConcurrentModificationException();
}
}
public boolean tryAdvance(Consumer<? super V> action) {
int hi;
if (action == null)
throw new NullPointerException();
Node<K,V>[] tab = map.table;
if (tab != null && tab.length >= (hi = getFence()) && index >= 0) {
while (current != null || index < hi) {
if (current == null)
current = tab[index++];
else {
V v = current.value;
current = current.next;
action.accept(v);
if (map.modCount != expectedModCount)
throw new ConcurrentModificationException();
return true;
}
}
}
return false;
}
public int characteristics() {
return (fence < 0 || est == map.size ? Spliterator.SIZED : 0);
}
}
static final class EntrySpliterator<K,V>
extends HashMapSpliterator<K,V>
implements Spliterator<Map.Entry<K,V>> {
EntrySpliterator(HashMap<K,V> m, int origin, int fence, int est,
int expectedModCount) {
super(m, origin, fence, est, expectedModCount);
}
public EntrySpliterator<K,V> trySplit() {
int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
return (lo >= mid || current != null) ? null :
new EntrySpliterator<>(map, lo, index = mid, est >>>= 1,
expectedModCount);
}
public void forEachRemaining(Consumer<? super Map.Entry<K,V>> action) {
int i, hi, mc;
if (action == null)
throw new NullPointerException();
HashMap<K,V> m = map;
Node<K,V>[] tab = m.table;
if ((hi = fence) < 0) {
mc = expectedModCount = m.modCount;
hi = fence = (tab == null) ? 0 : tab.length;
}
else
mc = expectedModCount;
if (tab != null && tab.length >= hi &&
(i = index) >= 0 && (i < (index = hi) || current != null)) {
Node<K,V> p = current;
current = null;
do {
if (p == null)
p = tab[i++];
else {
action.accept(p);
p = p.next;
}
} while (p != null || i < hi);
if (m.modCount != mc)
throw new ConcurrentModificationException();
}
}
public boolean tryAdvance(Consumer<? super Map.Entry<K,V>> action) {
int hi;
if (action == null)
throw new NullPointerException();
Node<K,V>[] tab = map.table;
if (tab != null && tab.length >= (hi = getFence()) && index >= 0) {
while (current != null || index < hi) {
if (current == null)
current = tab[index++];
else {
Node<K,V> e = current;
current = current.next;
action.accept(e);
if (map.modCount != expectedModCount)
throw new ConcurrentModificationException();
return true;
}
}
}
return false;
}
public int characteristics() {
return (fence < 0 || est == map.size ? Spliterator.SIZED : 0) |
Spliterator.DISTINCT;
}
}
/* ------------------------------------------------------------ */
// LinkedHashMap support
/*
* The following package-protected methods are designed to be
* overridden by LinkedHashMap, but not by any other subclass.
* Nearly all other internal methods are also package-protected
* but are declared final, so can be used by LinkedHashMap, view
* classes, and HashSet.
*/
// 创建一个新的单向链表节点
Node<K,V> newNode(int hash, K key, V value, Node<K,V> next) {
return new Node<>(hash, key, value, next);
}
// For conversion from TreeNodes to plain nodes
Node<K,V> replacementNode(Node<K,V> p, Node<K,V> next) {
return new Node<>(p.hash, p.key, p.value, next);
}
// Create a tree bin node
// 创建一个新的树节点
TreeNode<K,V> newTreeNode(int hash, K key, V value, Node<K,V> next) {
return new TreeNode<>(hash, key, value, next);
}
// For treeifyBin
// 将单向链表节点替换为树节点
TreeNode<K,V> replacementTreeNode(Node<K,V> p, Node<K,V> next) {
return new TreeNode<>(p.hash, p.key, p.value, next);
}
/**
* Reset to initial default state. Called by clone and readObject.
*/
void reinitialize() {
table = null;
entrySet = null;
keySet = null;
values = null;
modCount = 0;
threshold = 0;
size = 0;
}
// Callbacks to allow LinkedHashMap post-actions
void afterNodeAccess(Node<K,V> p) { }
void afterNodeInsertion(boolean evict) { }
void afterNodeRemoval(Node<K,V> p) { }
// Called only from writeObject, to ensure compatible ordering.
void internalWriteEntries(java.io.ObjectOutputStream s) throws IOException {
Node<K,V>[] tab;
if (size > 0 && (tab = table) != null) {
for (Node<K,V> e : tab) {
for (; e != null; e = e.next) {
s.writeObject(e.key);
s.writeObject(e.value);
}
}
}
}
/* ------------------------------------------------------------ */
// Tree bins
/**
* Entry for Tree bins. Extends LinkedHashMap.Entry (which in turn
* extends Node) so can be used as extension of either regular or
* linked node.
*/
static final class TreeNode<K,V> extends LinkedHashMap.Entry<K,V> {
TreeNode<K,V> parent; // 父节点
TreeNode<K,V> left; // 左孩子节点
TreeNode<K,V> right; // 右孩子节点
TreeNode<K,V> prev; // needed to unlink next upon deletion
boolean red; // 红色还是黑色
TreeNode(int hash, K key, V val, Node<K,V> next) {
super(hash, key, val, next);
}
/**
* Returns root of tree containing this node.
*/
final TreeNode<K,V> root() {
// 获取当前节点的树根节点
for (TreeNode<K,V> r = this, p;;) {
if ((p = r.parent) == null)
return r;
r = p;
}
}
/**
* Ensures that the given root is the first node of its bin.
*/
static <K,V> void moveRootToFront(Node<K,V>[] tab, TreeNode<K,V> root) {
int n;
if (root != null && tab != null && (n = tab.length) > 0) {
int index = (n - 1) & root.hash;
TreeNode<K,V> first = (TreeNode<K,V>)tab[index];
if (root != first) {
Node<K,V> rn;
tab[index] = root;
TreeNode<K,V> rp = root.prev;
if ((rn = root.next) != null)
((TreeNode<K,V>)rn).prev = rp;
if (rp != null)
rp.next = rn;
if (first != null)
first.prev = root;
root.next = first;
root.prev = null;
}
assert checkInvariants(root);
}
}
/**
* Finds the node starting at root p with the given hash and key.
* The kc argument caches comparableClassFor(key) upon first use
* comparing keys.
*/
final TreeNode<K,V> find(int h, Object k, Class<?> kc) {
TreeNode<K,V> p = this;
do {
int ph, dir; K pk;
// pl 当前节点的左侧子节点，pr 当前节点的右侧子节点
TreeNode<K,V> pl = p.left, pr = p.right, q;
// 当前节点的 hash 值大于目标哈希值
if ((ph = p.hash) > h)
// 往左侧查找
p = pl;
else if (ph < h)
// 往右侧查找
p = pr;
// 哈希值相等，并且节点的键和目标键引用相等或 equals 相等，则表示找到目标树节点，字节返回。
else if ((pk = p.key) == k || (k != null && k.equals(pk)))
return p;
// 左孩子为 null，则更新 parent 为右孩子
else if (pl == null)
p = pr;
// 右孩子为 null，则更新 parent 为左孩子
else if (pr == null)
p = pl;
else if ((kc != null ||
(kc = comparableClassFor(k)) != null) &&
(dir = compareComparables(kc, k, pk)) != 0)
p = (dir < 0) ? pl : pr;
else if ((q = pr.find(h, k, kc)) != null)
return q;
else
p = pl;
// 一直查找到没有左右孩子为止
} while (p != null);
return null;
}
/**
* Calls find for root node.
*/
final TreeNode<K,V> getTreeNode(int h, Object k) {
return ((parent != null) ? root() : this).find(h, k, null);
}
/**
* Tie-breaking utility for ordering insertions when equal
* hashCodes and non-comparable. We don‘t require a total
* order, just a consistent insertion rule to maintain
* equivalence across rebalancings. Tie-breaking further than
* necessary simplifies testing a bit.
*/
static int tieBreakOrder(Object a, Object b) {
int d;
// 先根据类的全限定名称进行比较，如果一致，则根据 System.identityHashCode 值进行比较
if (a == null || b == null ||
(d = a.getClass().getName().
compareTo(b.getClass().getName())) == 0)
d = (System.identityHashCode(a) <= System.identityHashCode(b) ?
-1 : 1);
return d;
}
/**
* Forms tree of the nodes linked from this node.
* 将单向链表红黑树化
*/
final void treeify(Node<K,V>[] tab) {
TreeNode<K,V> root = null; // 定义树的根节点
for (TreeNode<K,V> x = this, next; x != null; x = next) {
// 获取下一个节点
next = (TreeNode<K,V>)x.next;
// 将树节点的左右孩子置为 null
x.left = x.right = null;
if (root == null) { // 如果还未设置根节点
x.parent = null; // 将当前节点的父节点设置为 null
x.red = false; // 颜色为黑色
root = x; // 根节点指向当前节点
}
else { // 如果已经存在根节点了
K k = x.key; // 获取单向链表节点的键
int h = x.hash; // 获取节点的哈希值
Class<?> kc = null;
for (TreeNode<K,V> p = root;;) { // 从根节点开始遍历
int dir, ph;
K pk = p.key; // 根节点的键
if ((ph = p.hash) > h) // 根节点的哈希值 > 当前节点的哈希值
dir = -1; // 标识当前节点会放置在根节点的左侧
else if (ph < h) // 根节点的哈希值 < 当前节点的哈希值
dir = 1; // 标识当前节点会放置在根节点的右侧
/**
* 如果当前节点和根节点的哈希值一致，
* 如果当前链表节点的 key实现了 comparable接口，并且当前根节点和链表节点是相同 Class的实例，那么通过 compareTo 的方式再比较两者
*/
else if ((kc == null &&
(kc = comparableClassFor(k)) == null) ||
(dir = compareComparables(kc, k, pk)) == 0)
// 如果还是一致，则通过 tieBreakOrder 进行比较
dir = tieBreakOrder(k, pk);
TreeNode<K,V> xp = p; // 保存当前树节点
/**
* 如果 dir <= 0：当前链表节点需要放置在当前树节点的左侧，但不一定是该树节点的左孩子。
* 如果 dir > 0 ：当前链表节点需要放置在当前树节点的右侧，但不一定是该树节点的右孩子。
* 如果当前树节点的左侧或右侧孩子为 null，则直接插入当前节点，
* 否则获取到当前节点的左侧子节点【dir <= 0】或右侧子节点【dir > 0】，继续循环。
*/
if ((p = (dir <= 0) ? p.left : p.right) == null) {
x.parent = xp; // 设置单向链表节点的父节点为当前树节点
if (dir <= 0)
xp.left = x; // 如果 dir <= 0，则将链表节点设置为当前树节点的左侧子节点
else
xp.right = x; // 否则将链表节点设置为当前树节点的右侧子节点
// 重新平衡红黑树，并获取新的根节点
root = balanceInsertion(root, x);
break;
}
}
}
}
// 将根节点设置为 table 中 bucket 的首节点
moveRootToFront(tab, root);
}
/**
* Returns a list of non-TreeNodes replacing those linked from
* this node.
*/
final Node<K,V> untreeify(HashMap<K,V> map) {
// 定义 head 和 tail 节点
Node<K,V> hd = null, tl = null;
for (Node<K,V> q = this; q != null; q = q.next) {
// 将树节点转换为单链表节点
Node<K,V> p = map.replacementNode(q, null);
// 如果还没有尾节点，则将当前节点设置为当前节点【当前节点是第一个节点】
if (tl == null)
hd = p;
else
// 已经有尾节点了，则将尾节点的后置节点设置为当前节点
tl.next = p;
// 将当前节点设置为尾节点
tl = p;
}
// 返回头节点
return hd;
}
/**
* Tree version of putVal.
*/
final TreeNode<K,V> putTreeVal(HashMap<K,V> map, Node<K,V>[] tab,
int h, K k, V v) {
Class<?> kc = null;
boolean searched = false;
// 获取树根节点
TreeNode<K,V> root = (parent != null) ? root() : this;
for (TreeNode<K,V> p = root;;) {
int dir, ph; K pk;
// 当前节点的哈希值 > 新增节点的哈希值
if ((ph = p.hash) > h)
dir = -1; // 标记新增节点需要放置在当前树节点左侧
else if (ph < h) // 当前节点的哈希值 < 新增节点的哈希值
dir = 1; // 标记新增节点需要放置在当前树节点右侧
// 如果当前树节点和新增节点哈希值一致，并且键引用相等或 equals 相等，表示当前键已经存在，则直接返回当前树节点
else if ((pk = p.key) == k || (k != null && k.equals(pk)))
return p;
// 如果当前树节点和新增节点哈希值一致，
else if ((kc == null &&
(kc = comparableClassFor(k)) == null) ||
(dir = compareComparables(kc, k, pk)) == 0) {
/**
* searched 标识是否已经对比过当前节点的左右子树。
* 如果还没有遍历过，那么就递归遍历对比，如果找到和新增节点键相等的节点，则直接返回。
* 如果还是没有找到和新增节点键相等的节点，那说明应该创建一个新节点了。
*/
if (!searched) {
TreeNode<K,V> q, ch;
searched = true;
/**
* 如果左子节点不为 null，则递归查找左子树，如果右子节点不为 null，则递归查找右子树，
* 如果找到则立刻返回该节点。
*/
if (((ch = p.left) != null &&
(q = ch.find(h, k, kc)) != null) ||
((ch = p.right) != null &&
(q = ch.find(h, k, kc)) != null))
return q;
}
dir = tieBreakOrder(k, pk);
}
TreeNode<K,V> xp = p; // 记录当前树节点
if ((p = (dir <= 0) ? p.left : p.right) == null) {
Node<K,V> xpn = xp.next; // 获取单向链表结构中当前树节点的后置节点
// 构造树节点
TreeNode<K,V> x = map.newTreeNode(h, k, v, xpn);
if (dir <= 0)
xp.left = x; // 将新节点设置为当前树节点的左孩子
else
xp.right = x; // 将新节点设置为当前树节点的右孩子
xp.next = x; // 单向链表结构中当前树节点的后置节点更新为新增节点
x.parent = x.prev = xp; // 新增节点的前置节点和父节点都设置为当前树节点
if (xpn != null) // 更新当前树节点的旧后置节点的前置节点为新增树节点
((TreeNode<K,V>)xpn).prev = x;
// 平衡插入，并计算新的根节点，将其作为 table 中 bucket 的首节点
moveRootToFront(tab, balanceInsertion(root, x));
return null;
}
}
}
/**
* Removes the given node, that must be present before this call.
* This is messier than typical red-black deletion code because we
* cannot swap the contents of an interior node with a leaf
* successor that is pinned by "next" pointers that are accessible
* independently during traversal. So instead we swap the tree
* linkages. If the current tree appears to have too few nodes,
* the bin is converted back to a plain bin. (The test triggers
* somewhere between 2 and 6 nodes, depending on tree structure).
*/
final void removeTreeNode(HashMap<K,V> map, Node<K,V>[] tab,
boolean movable) {
int n;
if (tab == null || (n = tab.length) == 0)
return;
int index = (n - 1) & hash;
TreeNode<K,V> first = (TreeNode<K,V>)tab[index], root = first, rl;
TreeNode<K,V> succ = (TreeNode<K,V>)next, pred = prev;
if (pred == null)
tab[index] = first = succ;
else
pred.next = succ;
if (succ != null)
succ.prev = pred;
if (first == null)
return;
if (root.parent != null)
root = root.root();
if (root == null
|| (movable
&& (root.right == null
|| (rl = root.left) == null
|| rl.left == null))) {
tab[index] = first.untreeify(map); // too small
return;
}
TreeNode<K,V> p = this, pl = left, pr = right, replacement;
if (pl != null && pr != null) {
TreeNode<K,V> s = pr, sl;
while ((sl = s.left) != null) // find successor
s = sl;
boolean c = s.red; s.red = p.red; p.red = c; // swap colors
TreeNode<K,V> sr = s.right;
TreeNode<K,V> pp = p.parent;
if (s == pr) { // p was s‘s direct parent
p.parent = s;
s.right = p;
}
else {
TreeNode<K,V> sp = s.parent;
if ((p.parent = sp) != null) {
if (s == sp.left)
sp.left = p;
else
sp.right = p;
}
if ((s.right = pr) != null)
pr.parent = s;
}
p.left = null;
if ((p.right = sr) != null)
sr.parent = p;
if ((s.left = pl) != null)
pl.parent = s;
if ((s.parent = pp) == null)
root = s;
else if (p == pp.left)
pp.left = s;
else
pp.right = s;
if (sr != null)
replacement = sr;
else
replacement = p;
}
else if (pl != null)
replacement = pl;
else if (pr != null)
replacement = pr;
else
replacement = p;
if (replacement != p) {
TreeNode<K,V> pp = replacement.parent = p.parent;
if (pp == null)
root = replacement;
else if (p == pp.left)
pp.left = replacement;
else
pp.right = replacement;
p.left = p.right = p.parent = null;
}
TreeNode<K,V> r = p.red ? root : balanceDeletion(root, replacement);
if (replacement == p) { // detach
TreeNode<K,V> pp = p.parent;
p.parent = null;
if (pp != null) {
if (p == pp.left)
pp.left = null;
else if (p == pp.right)
pp.right = null;
}
}
if (movable)
moveRootToFront(tab, r);
}
/**
* Splits nodes in a tree bin into lower and upper tree bins,
* or untreeifies if now too small. Called only from resize;
* see above discussion about split bits and indices.
*
* @param map the map
* @param tab the table for recording bin heads
* @param index the index of the table being split
* @param bit the bit of hash to split on
*/
final void split(HashMap<K,V> map, Node<K,V>[] tab, int index, int bit) {
TreeNode<K,V> b = this;
// Relink into lo and hi lists, preserving order
TreeNode<K,V> loHead = null, loTail = null;
TreeNode<K,V> hiHead = null, hiTail = null;
int lc = 0, hc = 0;
for (TreeNode<K,V> e = b, next; e != null; e = next) {
next = (TreeNode<K,V>)e.next;
e.next = null;
if ((e.hash & bit) == 0) {
if ((e.prev = loTail) == null)
loHead = e;
else
loTail.next = e;
loTail = e;
++lc;
}
else {
if ((e.prev = hiTail) == null)
hiHead = e;
else
hiTail.next = e;
hiTail = e;
++hc;
}
}
if (loHead != null) {
if (lc <= UNTREEIFY_THRESHOLD)
tab[index] = loHead.untreeify(map);
else {
tab[index] = loHead;
if (hiHead != null) // (else is already treeified)
loHead.treeify(tab);
}
}
if (hiHead != null) {
if (hc <= UNTREEIFY_THRESHOLD)
tab[index + bit] = hiHead.untreeify(map);
else {
tab[index + bit] = hiHead;
if (loHead != null)
hiHead.treeify(tab);
}
}
}
/* ------------------------------------------------------------ */
// Red-black tree methods, all adapted from CLR
/**
* 以 p 节点为中心实现左旋
* https://github.com/CarpenterLee/JCFInternals/blob/master/markdown/5-TreeSet%20and%20TreeMap.md
*/
static <K,V> TreeNode<K,V> rotateLeft(TreeNode<K,V> root,
TreeNode<K,V> p) {
TreeNode<K,V> r, pp, rl;
if (p != null && (r = p.right) != null) {
if ((rl = p.right = r.left) != null)
rl.parent = p;
if ((pp = r.parent = p.parent) == null)
(root = r).red = false;
else if (pp.left == p)
pp.left = r;
else
pp.right = r;
r.left = p;
p.parent = r;
}
return root;
}
/**
* 以 p 节点为中心实现右旋
* created by ZXD at 16 Jul 2018 T 21:47:00
*/
static <K,V> TreeNode<K,V> rotateRight(TreeNode<K,V> root,
TreeNode<K,V> p) {
TreeNode<K,V> l, pp, lr;
if (p != null && (l = p.left) != null) {
if ((lr = p.left = l.right) != null)
lr.parent = p;
if ((pp = l.parent = p.parent) == null)
(root = l).red = false;
else if (pp.right == p)
pp.right = l;
else
pp.left = l;
l.right = p;
p.parent = l;
}
return root;
}
static <K,V> TreeNode<K,V> balanceInsertion(TreeNode<K,V> root,
TreeNode<K,V> x) {
x.red = true;
for (TreeNode<K,V> xp, xpp, xppl, xppr;;) {
if ((xp = x.parent) == null) {
x.red = false;
return x;
}
else if (!xp.red || (xpp = xp.parent) == null)
return root;
if (xp == (xppl = xpp.left)) {
if ((xppr = xpp.right) != null && xppr.red) {
xppr.red = false;
xp.red = false;
xpp.red = true;
x = xpp;
}
else {
if (x == xp.right) {
root = rotateLeft(root, x = xp);
xpp = (xp = x.parent) == null ? null : xp.parent;
}
if (xp != null) {
xp.red = false;
if (xpp != null) {
xpp.red = true;
root = rotateRight(root, xpp);
}
}
}
}
else {
if (xppl != null && xppl.red) {
xppl.red = false;
xp.red = false;
xpp.red = true;
x = xpp;
}
else {
if (x == xp.left) {
root = rotateRight(root, x = xp);
xpp = (xp = x.parent) == null ? null : xp.parent;
}
if (xp != null) {
xp.red = false;
if (xpp != null) {
xpp.red = true;
root = rotateLeft(root, xpp);
}
}
}
}
}
}
static <K,V> TreeNode<K,V> balanceDeletion(TreeNode<K,V> root,
TreeNode<K,V> x) {
for (TreeNode<K,V> xp, xpl, xpr;;) {
if (x == null || x == root)
return root;
else if ((xp = x.parent) == null) {
x.red = false;
return x;
}
else if (x.red) {
x.red = false;
return root;
}
else if ((xpl = xp.left) == x) {
if ((xpr = xp.right) != null && xpr.red) {
xpr.red = false;
xp.red = true;
root = rotateLeft(root, xp);
xpr = (xp = x.parent) == null ? null : xp.right;
}
if (xpr == null)
x = xp;
else {
TreeNode<K,V> sl = xpr.left, sr = xpr.right;
if ((sr == null || !sr.red) &&
(sl == null || !sl.red)) {
xpr.red = true;
x = xp;
}
else {
if (sr == null || !sr.red) {
if (sl != null)
sl.red = false;
xpr.red = true;
root = rotateRight(root, xpr);
xpr = (xp = x.parent) == null ?
null : xp.right;
}
if (xpr != null) {
xpr.red = (xp == null) ? false : xp.red;
if ((sr = xpr.right) != null)
sr.red = false;
}
if (xp != null) {
xp.red = false;
root = rotateLeft(root, xp);
}
x = root;
}
}
}
else { // symmetric
if (xpl != null && xpl.red) {
xpl.red = false;
xp.red = true;
root = rotateRight(root, xp);
xpl = (xp = x.parent) == null ? null : xp.left;
}
if (xpl == null)
x = xp;
else {
TreeNode<K,V> sl = xpl.left, sr = xpl.right;
if ((sl == null || !sl.red) &&
(sr == null || !sr.red)) {
xpl.red = true;
x = xp;
}
else {
if (sl == null || !sl.red) {
if (sr != null)
sr.red = false;
xpl.red = true;
root = rotateLeft(root, xpl);
xpl = (xp = x.parent) == null ?
null : xp.left;
}
if (xpl != null) {
xpl.red = (xp == null) ? false : xp.red;
if ((sl = xpl.left) != null)
sl.red = false;
}
if (xp != null) {
xp.red = false;
root = rotateRight(root, xp);
}
x = root;
}
}
}
}
}
/**
* Recursive invariant check
*/
static <K,V> boolean checkInvariants(TreeNode<K,V> t) {
TreeNode<K,V> tp = t.parent, tl = t.left, tr = t.right,
tb = t.prev, tn = (TreeNode<K,V>)t.next;
if (tb != null && tb.next != t)
return false;
if (tn != null && tn.prev != t)
return false;
if (tp != null && t != tp.left && t != tp.right)
return false;
if (tl != null && (tl.parent != t || tl.hash > t.hash))
return false;
if (tr != null && (tr.parent != t || tr.hash < t.hash))
return false;
if (t.red && tl != null && tl.red && tr != null && tr.red)
return false;
if (tl != null && !checkInvariants(tl))
return false;
if (tr != null && !checkInvariants(tr))
return false;
return true;
}
}
}
原文地址：https://www.cnblogs.com/zhuxudong/p/9320643.html