手撕HashMap源码
2021.09.06 15:30浏览量：93简介：手撕HashMap源码
手撕HashMap源码.md
文章已同步至GitHub开源项目: Java超神之路
HashMap一直是面试的重点。今天我们来了解了解它的源码吧！
首先看一下Map的继承结构图
源码分析
/*
* HashMap结构：哈希数组+链表/红黑树，key和value均可以为null
*
* 存储元素时，需要调用key的hashCode()方法，计算出一个哈希值
* 1.哈希值相同的元素，必定位于同一个哈希槽（链）上，但不能确定这两个元素是不是同位元素
* 在进一步判断key如果相等（必要时需要调用equals()方法）时，才能确定这两个元素属于同位元素
* 如果是存储同位元素，需要考虑是否允许覆盖旧值的问题
* 2.哈希值不同的元素，它们也可能位于同一个哈希槽（链）上，但它们肯定不是同位元素
*
* 注：HashMap非线程安全。如果需要考虑并发，则需要使用ConcurrentHashMap
*/
public class HashMap<K,V> extends AbstractMap<K,V> implements Map<K,V>, Cloneable, Serializable {
/**
* 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.
*/
static final int MAXIMUM_CAPACITY = 1 << 30; // 哈希数组最大容量
/**
* The default initial capacity - MUST be a power of two.
*/
static final int DEFAULT_INITIAL_CAPACITY = 16; // 哈希数组默认容量
/**
* The load factor used when none specified in constructor.
*/
static final float DEFAULT_LOAD_FACTOR = 0.75f; // HashMap默认装载因子（负荷系数）
/**
* 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.
*/
static final int TREEIFY_THRESHOLD = 8; // 某个哈希槽（链）上的元素数量增加到此值后，这些元素进入波动期，即将从链表转换为红黑树
/**
* 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.
*/
static final int MIN_TREEIFY_CAPACITY = 64; // 哈希数组的容量至少增加到此值，且满足TREEIFY_THRESHOLD的要求时，将链表转换为红黑树
/**
* 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.
*/
static final int UNTREEIFY_THRESHOLD = 6; // 哈希槽（链）上的红黑树上的元素数量减少到此值时，将红黑树转换为链表
/**
* 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.)
*/
transient Node<K,V>[] table; // 哈希数组（注：哈希数组的容量跟HashMap可以存储的元素数量不是一回事）
/**
* The number of key-value mappings contained in this map.
*/
transient int size; // HashMap中的元素数量
/**
* The load factor for the hash table.
*
* @serial
*/
final float loadFactor; // HashMap当前使用的装载因子
/**
* The next size value at which to resize (capacity * load factor).
*
* @serial
*
* The javadoc description is true upon serialization.
* Additionally, if the table array has not been allocated, this field holds the initial array capacity,
* or zero signifying DEFAULT_INITIAL_CAPACITY.
*/
int threshold; // HashMap扩容阈值，【一般】由（哈希数组容量*HashMap装载因子）计算而来，HashMap中元素数量超过该阈值时，哈希数组需要扩容
/**
* Holds cached entrySet(). Note that AbstractMap fields are used
* for keySet() and values().
*/
transient Set<Map.Entry<K,V>> entrySet; // entry集合
/**
* 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).
*/
transient int modCount; // 记录HashMap结构的修改次数
/*▼ 构造器 ████████████████████████████████████████████████████████████████████████████████┓ */
/**
* Constructs an empty {@code HashMap} with the default initial capacity (16) and the default load factor (0.75).
*/
// 初始化一个哈希数组容量为16，装载因子为0.75的HashMap
public HashMap() {
this.loadFactor = DEFAULT_LOAD_FACTOR; // all other fields defaulted
}
/**
* Constructs an empty {@code HashMap} with the specified initial
* capacity and the default load factor (0.75).
*
* @param initialCapacity the initial capacity.
* @throws IllegalArgumentException if the initial capacity is negative.
*/
// 初始化一个哈希数组容量为initialCapacity，装载因子为0.75的HashMap
public HashMap(int initialCapacity) {
this(initialCapacity, DEFAULT_LOAD_FACTOR);
}
/**
* Constructs an empty {@code HashMap} with the specified initial
* capacity and load factor.
*
* @param initialCapacity the initial capacity
* @param loadFactor the load factor
* @throws IllegalArgumentException if the initial capacity is negative
* or the load factor is nonpositive
*/
// 初始化一个哈希数组容量为initialCapacity，装载因子为loadFactor的HashMap
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);
}
// 初始化装载因子
this.loadFactor = loadFactor;
// 用初始容量信息来初始化HashMap扩容阈值，该阈值后续将作为初始化哈希数组的容量依据
this.threshold = tableSizeFor(initialCapacity);
}
/**
* 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}.
*
* @param m the map whose mappings are to be placed in this map
* @throws NullPointerException if the specified map is null
*/
// 使用指定的HashMap中的元素来初始化一个新的HashMap
public HashMap(Map<? extends K, ? extends V> m) {
this.loadFactor = DEFAULT_LOAD_FACTOR;
// 将指定HashMap中的元素存入到当前HashMap（允许覆盖）
putMapEntries(m, false);
}
/*▲ 构造器 ████████████████████████████████████████████████████████████████████████████████┛ */
/*▼ 存值 ████████████████████████████████████████████████████████████████████████████████┓ */
/**
* 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}.)
*/
// 将指定的元素（key-value）存入HashMap，并返回旧值，允许覆盖
public V put(K key, V value) {
return putVal(hash(key), key, value, false, true);
}
// 将指定的元素（key-value）存入HashMap，并返回旧值，不允许覆盖
@Override
public V putIfAbsent(K key, V value) {
return putVal(hash(key), key, value, true, true);
}
/**
* 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.
*
* @param m mappings to be stored in this map
*
* @throws NullPointerException if the specified map is null
*/
// 将指定Map中的元素存入到当前Map（允许覆盖）
public void putAll(Map<? extends K, ? extends V> map) {
putMapEntries(map, true);
}
/*▲ 存值 ████████████████████████████████████████████████████████████████████████████████┛ */
/*▼ 取值 ████████████████████████████████████████████████████████████████████████████████┓ */
/**
* 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.
*
* @see #put(Object, Object)
*/
// 根据指定的key获取对应的value，如果不存在，则返回null
public V get(Object key) {
// 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null
Node<K,V> e = getNode(hash(key), key);
return e == null ? null : e.value;
}
// 根据指定的key获取对应的value，如果不存在，则返回指定的默认值defaultValue
@Override
public V getOrDefault(Object key, V defaultValue) {
// 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null
Node<K,V> e = getNode(hash(key), key);
return e == null ? defaultValue : e.value;
}
/*▲ 取值 ████████████████████████████████████████████████████████████████████████████████┛ */
/*▼ 移除 ████████████████████████████████████████████████████████████████████████████████┓ */
/**
* Removes the mapping for the specified key from this map if present.
*
* @param key key whose mapping is to be removed from the map
*
* @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}.)
*/
// 移除拥有指定key的元素，并返回刚刚移除的元素的值
public V remove(Object key) {
Node<K, V> e;
return (e = removeNode(hash(key), key, null, false, true)) == null ? null : e.value;
}
// 移除拥有指定key和value的元素，返回值表示是否移除成功
@Override
public boolean remove(Object key, Object value) {
return removeNode(hash(key), key, value, true, true) != null;
}
/**
* Removes all of the mappings from this map.
* The map will be empty after this call returns.
*/
// 清空HashMap中所有元素
public void clear() {
Node<K, V>[] tab;
modCount++;
if((tab = table) != null && size>0) {
size = 0;
Arrays.fill(tab, null);
}
}
/*▲ 移除 ████████████████████████████████████████████████████████████████████████████████┛ */
/*▼ 替换 ████████████████████████████████████████████████████████████████████████████████┓ */
// 将拥有指定key的元素的值替换为newValue，并返回刚刚替换的元素的值（替换失败返回null）
@Override
public V replace(K key, V newValue) {
// 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null
Node<K,V> e = getNode(hash(key), key);
if (e != null) {
V oldValue = e.value;
e.value = newValue;
afterNodeAccess(e);
return oldValue;
}
return null;
}
// 将拥有指定key和oldValue的元素的值替换为newValue，返回值表示是否成功替换
@Override
public boolean replace(K key, V oldValue, V newValue) {
// 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null
Node<K,V> e = getNode(hash(key), key);
V v;
if (e != null && ((v = e.value) == oldValue || (v != null && v.equals(oldValue)))) {
e.value = newValue;
afterNodeAccess(e);
return true;
}
return false;
}
// 替换当前HashMap中的所有元素，替换策略由function决定，function的入参是元素的key和value，出参作为新值
@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();
}
}
}
/*▲ 替换 ████████████████████████████████████████████████████████████████████████████████┛ */
/*▼ 包含查询 ████████████████████████████████████████████████████████████████████████████████┓ */
/**
* Returns {@code true} if this map contains a mapping for the
* specified key.
*
* @param key The key whose presence in this map is to be tested
*
* @return {@code true} if this map contains a mapping for the specified
* key.
*/
// 判断HashMap中是否存在指定key的元素
public boolean containsKey(Object key) {
// 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null
Node<K,V> e = getNode(hash(key), key);
return e != null;
}
/**
* Returns {@code true} if this map maps one or more keys to the
* specified value.
*
* @param value value whose presence in this map is to be tested
*
* @return {@code true} if this map maps one or more keys to the
* specified value
*/
// 判断HashMap中是否存在指定value的元素
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;
}
/*▲ 包含查询 ████████████████████████████████████████████████████████████████████████████████┛ */
/*▼ 视图 ████████████████████████████████████████████████████████████████████████████████┓ */
/**
* 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.
*
* @return a set view of the keys contained in this map
*/
// 获取HashMap中key的集合
public Set<K> keySet() {
Set<K> ks = keySet;
if(ks == null) {
ks = new KeySet();
keySet = ks;
}
return ks;
}
/**
* 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
*/
// 获取HashMap中value的集合
public Collection<V> values() {
Collection<V> vs = values;
if(vs == null) {
vs = new Values();
values = vs;
}
return vs;
}
/**
* 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
*/
// 获取HashMap中key-value对的集合
public Set<Map.Entry<K, V>> entrySet() {
Set<Map.Entry<K, V>> es;
return (es = entrySet) == null ? (entrySet = new EntrySet()) : es;
}
/*▲ 视图 ████████████████████████████████████████████████████████████████████████████████┛ */
/*▼ 遍历 ████████████████████████████████████████████████████████████████████████████████┓ */
// 遍历HashMap中的元素，并对其应用action操作，action的入参是元素的key和value
@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();
}
}
}
/*▲ 遍历 ████████████████████████████████████████████████████████████████████████████████┛ */
/*▼ 重新映射 ████████████████████████████████████████████████████████████████████████████████┓ */
/**
* {@inheritDoc}
*
* <p>This method will, on a best-effort basis, throw a
* {@link ConcurrentModificationException} if it is detected that the
* remapping function modifies this map during computation.
*
* @throws ConcurrentModificationException if it is detected that the
* remapping function modified this map
*/
/*
* 插入/删除/替换操作，返回新值（可能为null）
* 此方法的主要意图：使用备用value和旧value创造的新value来更新旧value
*
* 注：以下流程图中，涉及到判断(◇)时，纵向代表【是】，横向代表【否】。此外，使用★代表计算。
*
* ●查找同位元素●
* |
* ↓
* ◇存在同位元素◇ --→ ★新value=备用value★ --→ ■【插入】新value■
* | 是 否
* ↓
* ◇旧value不为null --→ ★新value=备用value★ --→ ■新value【替换】旧value■
* | 是 否
* ↓
* ★新value=(旧value, 备用value)★
* |
* ↓
* ◇新value不为null◇ --→ ■【删除】同位元素■
* | 是 否
* ↓
* ■新value【替换】旧value■
*/
@Override
public V merge(K key, V bakValue, BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
if(bakValue == 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) {
// 初始化哈希数组，或者对哈希数组扩容，返回新的哈希数组
tab = resize();
n = tab.length;
}
// 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null
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);
}
}
// 如果找到了同位元素
if(old != null) {
V newValue;
// 确定应用到目标元素上的新值
if(old.value != null) {
int mc = modCount;
newValue = remappingFunction.apply(old.value, bakValue);
if(mc != modCount) {
throw new ConcurrentModificationException();
}
} else {
newValue = bakValue;
}
// 如果新值不为null，直接替换旧值
if(newValue != null) {
old.value = newValue;
afterNodeAccess(old);
} else {
// 如果新值为null，则会移除该元素
removeNode(hash, key, null, false, true);
}
return newValue;
}
// 如果没找到目标元素，但是传入的value不为null，则向HashMap中插入新元素
if(bakValue != null) {
if(t != null) {
t.putTreeVal(this, tab, hash, key, bakValue);
} else {
tab[i] = newNode(hash, key, bakValue, first);
if(binCount >= TREEIFY_THRESHOLD - 1) {
treeifyBin(tab, hash);
}
}
++modCount;
++size;
afterNodeInsertion(true);
}
return bakValue;
}
/**
* {@inheritDoc}
*
* <p>This method will, on a best-effort basis, throw a
* {@link ConcurrentModificationException} if it is detected that the
* remapping function modifies this map during computation.
*
* @throws ConcurrentModificationException if it is detected that the
* remapping function modified this map
*/
/*
* 插入/删除/替换操作，返回新值（可能为null）
* 此方法的主要意图：使用key和旧value创造的新value来更新旧value
*
* 注：以下流程图中，涉及到判断(◇)时，纵向代表【是】，横向代表【否】。此外，使用★代表计算。
*
* ●查找同位元素●
* |
* ↓
* ◇存在同位元素◇ --→ ★新value=(key, null)★
* | 是 否 |
* ↓ |
* ★新value=(key, 旧value)★ |
* ├---------------------------┘
* ↓
* ◇新value不为null◇ --→ ■如果存在同位元素，则【删除】同位元素■
* | 是 否
* ↓
* ■ 存在同位元素，则新value【替换】旧value■
* ■不存在同位元素，则【插入】新value ■
*/
@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) {
// 初始化哈希数组，或者对哈希数组扩容，返回新的哈希数组
tab = resize();
n = tab.length;
}
// 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null
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;
// 利用key和旧的value计算一个新的value
V newValue = remappingFunction.apply(key, oldValue);
if(mc != modCount) {
throw new ConcurrentModificationException();
}
// 如果存在同位元素
if(old != null) {
if(newValue != null) {
old.value = newValue;
afterNodeAccess(old);
} else {
removeNode(hash, key, null, false, true);
}
} else if(newValue != null) {
if(t != null) {
t.putTreeVal(this, tab, hash, key, newValue);
} else {
tab[i] = newNode(hash, key, newValue, first);
if(binCount >= TREEIFY_THRESHOLD - 1) {
treeifyBin(tab, hash);
}
}
modCount = mc + 1;
++size;
afterNodeInsertion(true);
}
return newValue;
}
/**
* {@inheritDoc}
*
* <p>This method will, on a best-effort basis, throw a
* {@link ConcurrentModificationException} if it is detected that the
* remapping function modifies this map during computation.
*
* @throws ConcurrentModificationException if it is detected that the
* remapping function modified this map
*/
/*
* 删除/替换操作，返回新值（可能为null）
* 此方法的主要意图：存在同位元素，且旧value不为null时，使用key和旧value创造的新value来更新旧value
*
* 注：以下流程图中，涉及到判断(◇)时，纵向代表【是】，横向代表【否】。此外，使用★代表计算。
*
* ●查找同位元素●
* |
* ↓
* ◇存在同位元素 && 旧value不为null◇
* |
* ↓
* ★新value=(key, 旧value)★
* |
* ↓
* ◇新value不为null◇ --→ ■【删除】同位元素■
* |
* ↓
* ■新value【替换】旧value■
*/
@Override
public V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
if(remappingFunction == null) {
throw new NullPointerException();
}
// 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null
Node<K, V> e = getNode(hash(key), key);
V oldValue;
// 如果同位元素存在，且旧的值不为null
if(e != null && (oldValue = e.value) != null) {
int mc = modCount;
// 利用key和旧的value计算一个新的value
V newValue = remappingFunction.apply(key, oldValue);
if(mc != modCount) {
throw new ConcurrentModificationException();
}
// 如果新的value不为null，则【替换】
if(newValue != null) {
e.value = newValue;
afterNodeAccess(e);
return newValue;
}
// 如果新的value为null，则【删除】
removeNode(hash(key), key, null, false, true);
}
return null;
}
/**
* {@inheritDoc}
*
* <p>This method will, on a best-effort basis, throw a
* {@link ConcurrentModificationException} if it is detected that the
* mapping function modifies this map during computation.
*
* @throws ConcurrentModificationException if it is detected that the
* mapping function modified this map
*/
/*
* 插入/替换操作，返回新值（可能为null）
* 此方法的主要意图：不存在同位元素，或旧value为null时，使用key创造的新value来更新旧value。如果同位元素旧值不为空，则直接返回旧值。
*
* 注：以下流程图中，涉及到判断(◇)时，纵向代表【是】，横向代表【否】。此外，使用★代表计算。
*
* ●查找同位元素●
* |
* ↓
* ◇存在同位元素 && 旧value不为null◇ --→ ★新value=(key)★
* 否 |
* ↓
* ◇新value不为null◇
* |
* ↓
* ■ 存在同位元素，则新value【替换】旧value■
* ■不存在同位元素，则【插入】新value ■
*/
@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) {
// 初始化哈希数组，或者对哈希数组扩容，返回新的哈希数组
tab = resize();
n = tab.length;
}
// 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null
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;
// 如果同位元素存在，且旧的value不是null，直接返回
if(old != null && (oldValue = old.value) != null) {
afterNodeAccess(old);
return oldValue;
}
}
int mc = modCount;
// 对key应用mappingFunction函数，计算出一个新的value
V newValue = mappingFunction.apply(key);
if(mc != modCount) {
throw new ConcurrentModificationException();
}
// 新的value为null
if(newValue == null) {
return null;
}
// 同位元素存在，且旧的value为null，新的value不为null，则用新的value【替换】旧的value
if(old != null) {
old.value = newValue;
afterNodeAccess(old);
return newValue;
}
// 如果不存在同位元素，则【插入】key和新的value为一个新元素
if(t != null) {
t.putTreeVal(this, tab, hash, key, newValue);
} else {
tab[i] = newNode(hash, key, newValue, first);
if(binCount >= TREEIFY_THRESHOLD - 1) {
treeifyBin(tab, hash);
}
}
modCount = mc + 1;
++size;
afterNodeInsertion(true);
return newValue;
}
/*▲ 重新映射 ████████████████████████████████████████████████████████████████████████████████┛ */
/*▼ LinkedHashMap ████████████████████████████████████████████████████████████████████████████████┓ */
/*
* 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.
*/
// 创建一个普通Node
Node<K, V> newNode(int hash, K key, V value, Node<K, V> next) {
return new Node<>(hash, key, value, next);
}
// 创建一个红黑树的TreeNode
TreeNode<K, V> newTreeNode(int hash, K key, V value, Node<K, V> next) {
return new TreeNode<>(hash, key, value, next);
}
// 从红黑树的TreeNode转换为一个普通Node
Node<K, V> replacementNode(Node<K, V> p, Node<K, V> next) {
return new Node<>(p.hash, p.key, p.value, next);
}
// 从普通Node转换为一个红黑树的TreeNode
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.
*/
// 重置当前HashMap，清空一切参数
void reinitialize() {
table = null;
entrySet = null;
keySet = null;
values = null;
modCount = 0;
threshold = 0;
size = 0;
}
// 插入一个新元素时的回调
void afterNodeInsertion(boolean evict) {
}
// 移除一个新元素时的回调
void afterNodeRemoval(Node<K, V> p) {
}
// 访问一个新元素时的回调
void afterNodeAccess(Node<K, V> p) {
}
/* Called only from writeObject, to ensure compatible ordering */
// 用于序列化过程
void internalWriteEntries(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);
}
}
}
}
/*▲ LinkedHashMap ████████████████████████████████████████████████████████████████████████████████┛ */
/*▼ 杂项 ████████████████████████████████████████████████████████████████████████████████┓ */
/**
* Returns the number of key-value mappings in this map.
*
* @return the number of key-value mappings in this map
*/
// 获取HashMap中的元素数量
public int size() {
return size;
}
/**
* Returns {@code true} if this map contains no key-value mappings.
*
* @return {@code true} if this map contains no key-value mappings
*/
// 判断HashMap是否为空集
public boolean isEmpty() {
return size == 0;
}
/*▲ 杂项 ████████████████████████████████████████████████████████████████████████████████┛ */
/*▼ 序列化 ████████████████████████████████████████████████████████████████████████████████┓ */
private static final long serialVersionUID = 362498820763181265L;
/**
* Saves this map to a stream (that is, serializes it).
*
* @param s the stream
*
* @throws IOException if an I/O error occurs
* @serialData The <i>capacity</i> of the HashMap (the length of the
* bucket array) is emitted (int), followed by the
* <i>size</i> (an int, the number of key-value
* mappings), followed by the key (Object) and value (Object)
* for each key-value mapping. The key-value mappings are
* emitted in no particular order.
*/
private void writeObject(java.io.ObjectOutputStream s) throws IOException {
int buckets = capacity();
// Write out the threshold, loadfactor, and any hidden stuff
s.defaultWriteObject();
s.writeInt(buckets);
s.writeInt(size);
internalWriteEntries(s);
}
/**
* Reconstitutes this map from a stream (that is, deserializes it).
*
* @param s the stream
*
* @throws ClassNotFoundException if the class of a serialized object
* could not be found
* @throws IOException if an I/O error occurs
*/
private void readObject(java.io.ObjectInputStream s) throws IOException, ClassNotFoundException {
// Read in the threshold (ignored), loadfactor, and any hidden stuff
s.defaultReadObject();
reinitialize();
if(loadFactor<=0 || Float.isNaN(loadFactor)) {
throw new InvalidObjectException("Illegal load factor: " + loadFactor);
}
s.readInt(); // Read and ignore number of buckets
int mappings = s.readInt(); // Read number of mappings (size)
if(mappings<0) {
throw new InvalidObjectException("Illegal mappings count: " + mappings);
} else if(mappings>0) { // (if zero, use defaults)
// Size the table using given load factor only if within
// range of 0.25...4.0
float lf = Math.min(Math.max(0.25f, loadFactor), 4.0f);
float fc = (float) mappings / lf + 1.0f;
int cap = ((fc<DEFAULT_INITIAL_CAPACITY) ? DEFAULT_INITIAL_CAPACITY : (fc >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : tableSizeFor((int) fc));
float ft = (float) cap * lf;
threshold = ((cap<MAXIMUM_CAPACITY && ft<MAXIMUM_CAPACITY) ? (int) ft : Integer.MAX_VALUE);
// Check Map.Entry[].class since it's the nearest public type to
// what we're actually creating.
SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Map.Entry[].class, cap);
@SuppressWarnings({"rawtypes", "unchecked"})
Node<K, V>[] tab = (Node<K, V>[]) new Node[cap];
table = tab;
// Read the keys and values, and put the mappings in the HashMap
for(int i = 0; i<mappings; i++) {
@SuppressWarnings("unchecked")
K key = (K) s.readObject();
@SuppressWarnings("unchecked")
V value = (V) s.readObject();
putVal(hash(key), key, value, false, false);
}
}
}
/*▲ 序列化 ████████████████████████████████████████████████████████████████████████████████┛ */
/**
* Returns a shallow copy of this {@code HashMap} instance: the keys and
* values themselves are not cloned.
*
* @return a shallow copy of this map
*/
@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();
// 将当前HashMap中的元素存入到result（允许覆盖）
result.putMapEntries(this, false);
return result;
}
/**
* Computes key.hashCode() and spreads (XORs) higher bits of hash to lower.
* Because the table uses power-of-two masking, sets of hashes that vary only in bits above the current mask will always collide.
* (Among known examples are sets of Float keys holding consecutive whole numbers in small tables.)
* So we apply a transform that spreads the impact of higher bits downward.
* There is a tradeoff between speed, utility, and quality of bit-spreading.
* Because many common sets of hashes are already reasonably distributed (so don't benefit from spreading),
* and because we use trees to handle large sets of collisions in bins,
* we just XOR some shifted bits in the cheapest possible way to reduce systematic lossage,
* as well as to incorporate impact of the highest bits that would otherwise never be used in index calculations because of table bounds.
*/
/*
* 计算key的哈希值，在这个过程中会调用key的hashCode()方法
*
* key是一个对象的引用（可以看成地址）
* 理论上讲，key的值是否相等，跟计算出的哈希值是否相等，没有必然联系，一切都取决于hashCode()这个方法
*/
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.
*/
/*
* 检查Comparable接口是否有效
*
* 假设存在X类型的实例x，
* 如果X类型实现了Comparable接口，且接口中的类型参数是X自身，则返回X.class，
* 否则，将返回null，这代表X没有实现“有效”的Comparable接口
*
* 例如：
* class X implements Comparable<X> {
* // 。。。
* }
*
* X x = new X();
*
* 则：comparableClassFor(x)返回X.class
*/
static Class<?> comparableClassFor(Object x) {
// 是否实现了Comparable接口
if(x instanceof Comparable) {
Class<?> c = x.getClass();
// 快速判断。对于String类型的实例，则直接返回String.class
if(c == String.class) {
// bypass checks
return c;
}
// 获取当前类的父接口（可识别泛型类型和非泛型类型）
Type[] ts = c.getGenericInterfaces();
if(ts != null) {
for(Type t : ts) {
if(t instanceof ParameterizedType) {
ParameterizedType p = (ParameterizedType) t;
if(p.getRawType() == Comparable.class){
// 获取参数化类型中的实际参数（argument）
Type[] as = p.getActualTypeArguments();
if(as != null) {
if(as.length == 1){
/*
* 进一步判断，是否实现了“有效”的Comparable接口，
* “有效”的含义是，Comparable接口的参数为该类本身，
* 因为只有这样，才能对该类进行有效的内部比较
*/
if(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.
*/
// 返回k和x的比较结果
@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.
*/
/*
* 根据预期的容量cap计算出HashMap中的哈希数组实际需要分配的容量
* 如果输入值是2的冪，则原样返回，如果不是2的冪，则向上取就近的冪
* 比如输入13，返回16，输入17，返回32
*/
static final int tableSizeFor(int cap) {
int n = -1 >>> Integer.numberOfLeadingZeros(cap - 1);
return (n<0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
}
/**
* Implements Map.putAll and Map constructor.
*
* @param m the map
* @param evict false when initially constructing this map, else true (relayed to method afterNodeInsertion).
*/
// 将指定HashMap中的元素存入到当前HashMap（允许覆盖）
final void putMapEntries(Map<? extends K, ? extends V> map, boolean evict) {
int s = map.size();
if(s>0) {
// 如果当前HashMap的哈希数组还未初始化
if(table == null) { // pre-size
// 由HashMap中的元素数量反推哈希数组的最低容量要求
float ft = ((float) s / loadFactor) + 1.0F;
int t = ((ft<(float) MAXIMUM_CAPACITY) ? (int) ft : MAXIMUM_CAPACITY);
// 计算HashMap扩容阈值
if(t>threshold) {
threshold = tableSizeFor(t);
}
// 如果当前HashMap的哈希数组已存在，但是容量不足，则需要扩容
} else if(s>threshold) {
// 初始化哈希数组，或者对哈希数组扩容，返回新的哈希数组
resize();
}
for(Map.Entry<? extends K, ? extends V> e : map.entrySet()) {
K key = e.getKey();
V value = e.getValue();
// 向HashMap中存入新的元素，允许覆盖
putVal(hash(key), key, value, false, evict);
}
}
}
/**
* Implements Map.get and related methods.
*
* @param hash hash for key
* @param key the key
*
* @return the node, or null if none
*/
// 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null
final Node<K, V> getNode(int hash, Object key) {
Node<K, V>[] tab;
Node<K, V> first, e;
int n;
K k;
if((tab = table) != null && (n = tab.length)>0 && (first = tab[(n - 1) & hash]) != null) {
/*
* 对哈希槽（链）中的首个元素进行判断
*
* 只有哈希值一致（还说明不了key是否一致），且key也相同（必要时需要用到equals()方法）时，
* 这里才认定是存在同位元素（在HashMap中占据相同位置的元素）
*/
if(first.hash == hash && // always check first node
((k = first.key) == key || (key != null && key.equals(k)))) {
return first;
}
if((e = first.next) != null) {
// 如果是红黑树元素，则在红黑树中查找
if(first instanceof TreeNode) {
return ((TreeNode<K, V>) first).getTreeNode(hash, key);
}
// 遍历哈希槽（链）上后续的元素
do {
if(e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k)))) {
return e;
}
} while((e = e.next) != null);
}
}
return null;
}
/**
* Implements Map.put and related methods.
*
* @param hash hash for key
* @param key the key
* @param value the value to put
* @param onlyIfAbsent if true, don't change existing value
* @param evict if false, the table is in creation mode.
*
* @return previous value, or null if none
*/
/*
* 向当前Map中存入新的元素，并返回旧元素
*
* hash key的哈希值
* onlyIfAbsent 是否需要维持原状（不覆盖旧值）
* evict if false, the table is in creation mode.
*
* 返回同位元素的旧值（在当前Map中占据相同位置的元素）
* 如果不存在同位元素，即插入了新元素，则返回null
* 如果存在同位元素，但同位元素的旧值为null，那么也返回null
*/
final V putVal(int hash, K key, V value, boolean onlyIfAbsent, boolean evict) {
Node<K, V>[] tab; // 指向当前哈希数组
Node<K, V> p; // 指向待插入元素应当插入的位置
int n, i;
// 如果哈希数组还未初始化，或者容量无效，则需要初始化一个哈希数组
if((tab = table) == null || (n = tab.length) == 0) {
// 初始化哈希数组，或者对哈希数组扩容，返回新的哈希数组
tab = resize();
n = tab.length;
}
// p指向hash所在的哈希槽（链）上的首个元素
p = tab[i = (n - 1) & hash];
// 如果哈希槽为空，则在该槽上放置首个元素（普通Node）
if(p == null) {
tab[i] = newNode(hash, key, value, null);
// 如果哈希槽不为空，则需要在哈希槽后面链接更多的元素
} else {
Node<K, V> e;
K k;
/*
* 对哈希槽中的首个元素进行判断
*
* 只有哈希值一致（还说明不了key是否一致），且key也相同（必要时需要用到equals()方法）时，
* 这里才认定是存在同位元素（在HashMap中占据相同位置的元素）
*/
if(p.hash == hash && ((k = p.key) == key || (key != null && key.equals(k)))) {
e = p;
// 如果该哈希槽上链接的是红黑树结点，则需要调用红黑树的插入方法
} else if(p instanceof TreeNode) {
e = ((TreeNode<K, V>) p).putTreeVal(this, tab, hash, key, value);
} else {
// 遍历哈希槽后面链接的其他元素（binCount统计的是插入新元素之前遍历过的元素数量）
for(int binCount = 0; ; ++binCount) {
// 如果没有找到同位元素，则需要插入新元素
if((e = p.next) == null) {
// 插入一个普通结点
p.next = newNode(hash, key, value, null);
// 哈希槽（链）上的元素数量增加到TREEIFY_THRESHOLD后，这些元素进入波动期，即将从链表转换为红黑树
if(binCount >= TREEIFY_THRESHOLD - 1) { // -1 for 1st
treeifyBin(tab, hash);
}
break;
}
/*
* 对哈希槽后面链接的其他元素进行判断
*
* 只有哈希值一致（还说明不了key是否一致），且key也相同（必要时需要用到equals()方法）时，
* 这里才认定是存在同位元素（在HashMap中占据相同位置的元素）
*/
if(e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k)))) {
break;
}
p = e;
}
}
// 如果存在同位元素（在HashMap中占据相同位置的元素）
if(e != null) { // existing mapping for key
// 获取旧元素的值
V oldValue = e.value;
// 如果不需要维持原状（可以覆盖旧值），或者旧值为null
if(!onlyIfAbsent || oldValue == null) {
// 更新旧值
e.value = value;
}
afterNodeAccess(e);
// 返回覆盖前的旧值
return oldValue;
}
}
// HashMap的更改次数加一
++modCount;
// 如果哈希数组的容量已超过阈值，则需要对哈希数组扩容
if(++size>threshold) {
// 初始化哈希数组，或者对哈希数组扩容，返回新的哈希数组
resize();
}
afterNodeInsertion(evict);
// 如果插入的是全新的元素，在这里返回null
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
*/
/*
* 初始化哈希数组，或者对哈希数组扩容，返回新的哈希数组
*
* 注：哈希数组的容量跟HashMap存放的元素数量没有必然联系
* 哈希数组只存放一系列同位元素（在HashMap中占据相同位置的元素）中最早进来的那个
*/
final Node<K, V>[] resize() {
Node<K, V>[] oldTab = table;
// 旧容量
int oldCap = (oldTab == null) ? 0 : oldTab.length;
// 旧阈值
int oldThr = threshold;
// 新容量
int newCap;
// 新阈值，初始化为0
int newThr = 0;
// 如果哈希数组已经初始化（非首次进来）
if(oldCap>0) {
// 如果哈希表数组容量已经超过最大容量
if(oldCap >= MAXIMUM_CAPACITY) {
// 将HashMap的阈值更新为允许的最大值
threshold = Integer.MAX_VALUE;
// 不需要更改哈希数组（容量未发生变化），直接返回
return oldTab;
} else {
// 尝试将哈希表数组容量加倍
newCap = oldCap << 1;
// 如果容量成功加倍（没有达到上限），则将阈值也加倍
if(newCap<MAXIMUM_CAPACITY && oldCap >= DEFAULT_INITIAL_CAPACITY) {
newThr = oldThr << 1; // double threshold
}
}
// 如果哈希数组还未初始化（首次进来）
} else {
/* initial capacity was placed in threshold */
// 如果实例化HashMap时已经指定了初始容量，则将哈希数组当前容量初始化为与旧阈值一样大（初始容量与旧阈值的计算关系参见tableSizeFor()方法）
if(oldThr>0) {
newCap = oldThr;
/* zero initial threshold signifies using defaults */
// 如果实例化HashMap时没有指定初始容量，则使用默认的容量与阈值
} else {
newCap = DEFAULT_INITIAL_CAPACITY;
newThr = (int) (DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);
}
}
/*
* 至此，如果newThr==0，则可能有以下两种情形：
* 1.哈希数组已经初始化，且哈希数组的容量还未超出最大容量，
* 但是，在执行了加倍操作后，哈希数组的容量达到了上限
* 2.哈希数组还未初始化，但在实例化HashMap时指定了初始容量
*/
if(newThr == 0) {
float ft = (float) newCap * loadFactor;
newThr = newCap<MAXIMUM_CAPACITY && ft<(float) MAXIMUM_CAPACITY
? (int) ft // 针对第二种情况，将阈值更新为初始容量*装载因子
: Integer.MAX_VALUE; // 针对第一种情况，将阈值更新为最大值
}
// 更新阈值
threshold = newThr;
// 至此，说明哈希数组需要初始化，或者需要扩容，即创建新的哈希数组
@SuppressWarnings({"rawtypes", "unchecked"})
Node<K, V>[] newTab = (Node<K, V>[]) new Node[newCap];
table = newTab;
// 如果是扩容，则需要将旧元素复制到新容器
if(oldTab != null) {
for(int j = 0; j<oldCap; ++j) {
Node<K, V> e = oldTab[j];
// 如果当前哈希槽上存在元素
if(e != null) {
// 置空该哈希槽
oldTab[j] = null;
// 如果该哈希槽上只有一个元素
if(e.next == null) {
// 由于总容量变了，所以需要重新哈希
newTab[e.hash & (newCap - 1)] = e;
// 如果该哈希槽上链接了不止一个元素，且该元素是TreeNode类型
} else if(e instanceof TreeNode) {
// 拆分红黑树以适应新的容量要求
((TreeNode<K, V>) e).split(this, newTab, j, oldCap);
// 如果该哈希槽上链接了不止一个元素，且该元素是普通Node类型
} else { // preserve order
Node<K, V> loHead = null, loTail = null;
Node<K, V> hiHead = null, hiTail = null;
Node<K, V> next;
// 这里跟split()操作类似，将原有的结点分成两拨，以适应新的容量需求
do {
next = e.next;
if((e.hash & oldCap) == 0) {
if(loTail == null) {
loHead = e;
} else {
loTail.next = e;
}
loTail = e;
} else {
if(hiTail == null) {
hiHead = e;
} else {
hiTail.next = e;
}
hiTail = e;
}
} while((e = next) != null);
if(loTail != null) {
loTail.next = null;
newTab[j] = loHead;
}
if(hiTail != null) {
hiTail.next = null;
newTab[j + oldCap] = hiHead;
}
}
}
}
}
return newTab;
}
/**
* Replaces all linked nodes in bin at index for given hash unless
* table is too small, in which case resizes instead.
*/
/*
* 观察哈希槽（链）上处于波动期的元素，以决定下一步是扩容还是将链表转换为红黑树
*
* tab：待转换的链表
* hash：某元素的哈希值
*/
final void treeifyBin(Node<K, V>[] tab, int hash) {
int n;
// 哈希数组的容量还未达到形成一棵红黑树的最低要求
if(tab == null || (n = tab.length)<MIN_TREEIFY_CAPACITY) {
// 初始化哈希数组，或者对哈希数组扩容，返回新的哈希数组
resize();
// 满足从链表转换为红黑树的要求
} else {
// 计算哈希槽索引
int index = (n - 1) & hash;
Node<K, V> e = tab[index];
if(e!= null) {
TreeNode<K, V> hd = null, tl = null;
do {
// 将元素e从链表结点转换为红黑树结点
TreeNode<K, V> p = replacementTreeNode(e, null);
if(tl == null) {
hd = p;
} else {
p.prev = tl;
tl.next = p;
}
tl = p;
} while((e = e.next) != null);
if((tab[index] = hd) != null) {
// 遍历hd链表上的所有元素，创建一棵红黑树
hd.treeify(tab);
}
}
}
}
/* These methods are also used when serializing HashSets */
// 获取HashMap当前使用的装载因子
final float loadFactor() {
return loadFactor;
}
// 获取哈希数组的容量
final int capacity() {
return (table != null)
? table.length
: (threshold>0) ? threshold : DEFAULT_INITIAL_CAPACITY;
}
/**
* Implements Map.remove and related methods.
*
* @param hash hash for key
* @param key the key
* @param value the value to match if matchValue, else ignored
* @param matchValue if true only remove if value is equal
* @param movable if false do not move other nodes while removing
*
* @return the node, or null if none
*/
/*
* 从HashMap中移除指定的元素，并返回刚刚移除的元素（移除失败返回null）
*
* matchValue 移除元素时是否需要考虑value的匹配问题
* movable 移除元素后如果红黑树根结点发生了变化，那么是否需要改变结点在链表上的顺序
*/
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) {
Node<K, V> node = null, e;
K k;
V v;
/* 根据给定的key和hash（由key计算而来）查找对应的（同位）元素 */
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);
}
}
/*
* 从HashMap中移除匹配的元素
* 可能只需要匹配hash和key就行，也可能还要匹配value，这取决于matchValue参数
*/
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);
} else if(node == p) {
tab[index] = node.next;
} else {
p.next = node.next;
}
++modCount;
--size;
afterNodeRemoval(node);
return node;
}
}
return null;
}
/**
* Basic hash bin node, used for most entries. (See below for
* TreeNode subclass, and in LinkedHashMap for its Entry subclass.)
*/
// HashMap中的普通结点信息，每个Node代表一个元素，里面包含了key和value的信息
static class Node<K, V> implements Map.Entry<K, V> {
final int hash;
final K key;
V value;
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 V setValue(V newValue) {
V oldValue = value;
value = newValue;
return oldValue;
}
public final String toString() {
return key + "=" + value;
}
public final int hashCode() {
return Objects.hashCode(key) ^ Objects.hashCode(value);
}
public final boolean equals(Object o) {
if(o == this) {
return true;
}
if(o instanceof Map.Entry) {
Map.Entry<?, ?> e = (Map.Entry<?, ?>) o;
return Objects.equals(key, e.getKey()) && Objects.equals(value, e.getValue());
}
return false;
}
}
/**
* Entry for Tree bins. Extends LinkedHashMap.Entry (which in turn
* extends Node) so can be used as extension of either regular or
* linked node.
*/
// HashMap中的红黑树结点
static final class TreeNode<K,V> extends LinkedHashMap.Entry<K,V> {
TreeNode<K,V> parent; // red-black tree links
TreeNode<K,V> left;
TreeNode<K,V> right;
boolean red;
TreeNode<K,V> prev; // needed to unlink next upon deletion
// 仍然需要维护next链接
TreeNode(int hash, K key, V val, Node<K, V> next) {
super(hash, key, val, next);
}
/*▼ 创建/反创建 ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓┓ */
/**
* Forms tree of the nodes linked from this node.
*/
/*
* 遍历当前TreeNode链表上的所有元素，创建一棵红黑树
*
* 创建完成后，当前的TreeNode元素以及后面链接的那串元素具有链表与红黑树两种结构
* 其中，链表是靠着结点的prev和next来链接的
* 除此之外，由于创建红黑树的过程中，根结点可能会发生动态变化，
* 所以，在红黑树创建完成后，当前的TreeNode元素可能是，也可能不是红黑树的根结点，
* 如果当前的TreeNode元素不是红黑树的根结点，那么它在原来链表上的相对位置也会发生变化（通过moveRootToFront()方法调整）
*/
final void treeify(Node<K, V>[] tab) {
TreeNode<K, V> root = null;
// 遍历待插入元素
for(TreeNode<K, V> x = this, next; x != null; x = next) {
next = (TreeNode<K, V>) x.next;
x.left = x.right = null;
// 创建根结点
if(root == null) {
x.parent = null; // 根结点parent为null
x.red = false; // 根结点为黑色
root = x; // root指向根结点
} else {
K k = x.key;
int h = x.hash;
Class<?> kc = null;
// 遍历红黑树，将k所代表的元素插入到红黑树中合适的位置
for(TreeNode<K, V> p = root; ; ) {
int dir, ph;
K pk = p.key;
/*
* 判断待插入元素的插入位置，是向左查找？还是向右查找？
* 判断依据依次为：
* ┌──不相同，可以得出结果 ★
* ┌──不相同，直接得出结果 ★ ┌──类型一致───使用compareTo()方法判断──┤
* 判断hash ──┤ ┌──有效───检查参与比较的元素类型──┤ └───相同───┐
* └──相同───检查Comparable接口──┤ └───类型不一致───────────────────────────────────┼──调用tieBreakOrder()方法，可以得出结果 ★
* └───无效──────────────────────────────────────────────────────────────────────┘
*
*
*/
// 待插入结点的hash值较小，则向左搜寻合适的插入位置
if((ph = p.hash)>h) {
dir = -1;
// 待插入结点的hash值较大，则向右搜寻合适的插入位置
} else if(ph<h) {
dir = 1;
// 待插入结点的hash值出现了雷同
} else if((kc == null && (kc = comparableClassFor(k)) == null) // 如果k（的类类型）没有实现“有效”的Comparable接口
|| (dir = compareComparables(kc, k, pk)) == 0) { // 或者，待插入元素与已存在元素类型不同，无法比较
// 终极判等方式：使用对象的类名和对象本身的哈希码去比较两个对象的大小，而且返回值一定是-1或者是1
dir = tieBreakOrder(k, pk);
}
// 向指定的位置插入结点
TreeNode<K, V> xp = p;
if((p = (dir<=0) ? p.left : p.right) == null) {
x.parent = xp;
if(dir<=0) {
xp.left = x;
} else {
xp.right = x;
}
// 将元素x插入到红黑树root后，可能会破坏其平衡性，所以这里需要做出调整，保持红黑树的平衡
root = balanceInsertion(root, x);
break;
}
}
}
}
/*
* 由于红黑树根结点可能发生了变化，所以需要检查/调整链表顺序：
* 将root放入哈希数组tab的合适位置，且将root指向的元素移动到链表的头部
*/
moveRootToFront(tab, root);
}
/**
* Returns a list of non-TreeNodes replacing those linked from this node.
*/
// 遍历当前TreeNode红黑树上所有元素，创建一个链表
final Node<K, V> untreeify(HashMap<K, V> map) {
Node<K, V> hd = null, tl = null;
for(Node<K, V> q = this; q != null; q = q.next) {
Node<K, V> p = map.replacementNode(q, null);
if(tl == null) {
hd = p;
} else {
tl.next = p;
}
tl = p;
}
return hd;
}
/*▲ 创建/反创建 ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓┛ */
/*▼ 插入/删除 ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓┓ */
/**
* Tree version of putVal.
*/
// 向当前红黑树中插入元素
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;
// 获取当前红黑树的根结点
TreeNode<K, V> root = (parent != null) ? root() : this;
for(TreeNode<K, V> p = root; ; ) {
int dir, ph;
K pk;
if((ph = p.hash)>h) {
dir = -1;
} else if(ph<h) {
dir = 1;
} else if((pk = p.key) == k || (k != null && k.equals(pk))) {
return p;
} else if((kc == null && (kc = comparableClassFor(k)) == null) || (dir = compareComparables(kc, k, pk)) == 0) {
if(!searched) {
TreeNode<K, V> q, ch;
searched = true;
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;
}
}
// 终极判等方式：使用对象的类名和对象本身的哈希码去比较两个对象的大小，而且返回值一定是-1或者是1
dir = tieBreakOrder(k, pk);
}
TreeNode<K, V> xp = p;
if((p = (dir<=0) ? p.left : p.right) == null) {
Node<K, V> xpn = xp.next;
TreeNode<K, V> x = map.newTreeNode(h, k, v, xpn);
if(dir<=0) {
xp.left = x;
} else {
xp.right = x;
}
xp.next = x;
x.parent = x.prev = xp;
if(xpn != null) {
((TreeNode<K, V>) xpn).prev = x;
}
// 将元素x插入到红黑树root后，可能会破坏其平衡性，所以这里需要做出调整，保持红黑树的平衡
TreeNode<K, V> r = balanceInsertion(root, x);
/*
* 由于红黑树根结点可能发生了变化，所以需要检查/调整链表顺序：
* 将r放入哈希数组tab的合适位置，且将r指向的元素移动到链表的头部
*/
moveRootToFront(tab, r);
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).
*/
// 将元素从红黑树中移除
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) {
// 获取当前红黑树的根结点
root = root.root();
}
if(root == null
|| (movable && (root.right == null || (rl = root.left) == null || rl.left == null))) {
// 遍历红黑树first上所有元素，创建一个链表
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;
// find successor
while((sl = s.left) != null) {
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); // 将元素x从红黑树root移除后，可能会破坏其平衡性，所以这里需要做出调整，保持红黑树的平衡
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) {
/*
* 由于红黑树根结点可能发生了变化，所以需要检查/调整链表顺序：
* 将r放入哈希数组tab的合适位置，且将r指向的元素移动到链表的头部
*/
moveRootToFront(tab, r);
}
}
// 将元素x插入到红黑树root后，可能会破坏其平衡性，所以这里需要做出调整，保持红黑树的平衡
static <K, V> TreeNode<K, V> balanceInsertion(TreeNode<K, V> root, TreeNode<K, V> x) {
// 新插入的结点一律先设置为红色
x.red = true;
for(TreeNode<K, V> xp, xpp, xppl, xppr; ; ) {
if((xp = x.parent) == null) {
x.red = false;
return x;
}
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);
}
}
}
}
}
}
// 将元素x从红黑树root移除后，可能会破坏其平衡性，所以这里需要做出调整，保持红黑树的平衡
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) && 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) && xp.red;
if((sl = xpl.left) != null) {
sl.red = false;
}
}
if(xp != null) {
xp.red = false;
root = rotateRight(root, xp);
}
x = root;
}
}
}
}
}
// 左旋
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;
}
// 右旋
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;
}
/*▲ 插入/删除 ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓┛ */
/**
* Ensures that the given root is the first node of its bin.
*/
/*
* 在红黑树根结点可能发生变化时，需要检查/调整链表顺序：
* 将root放入哈希数组tab的合适位置，且将root指向的元素移动到链表的头部
*/
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) {
tab[index] = root;
TreeNode<K, V> rp = root.prev;
Node<K, V> rn = root.next;
if(rn != 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);
}
}
/**
* 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.
*/
// 终极判等方式：使用对象的类名和对象本身的哈希码去比较两个对象的大小，而且返回值一定是-1或者是1
static int tieBreakOrder(Object a, Object b) {
int d;
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;
}
/**
* Returns root of tree containing this node.
*/
// 获取当前红黑树的根结点
final TreeNode<K, V> root() {
for(TreeNode<K, V> r = this, p; ; ) {
if((p = r.parent) == null) {
return r;
}
r = p;
}
}
/**
* Finds the node starting at root p with the given hash and key.
* The kc argument caches comparableClassFor(key) upon first use
* comparing keys.
*/
// 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null
final TreeNode<K, V> find(int hash, Object key, Class<?> kc) {
TreeNode<K, V> p = this;
do {
int ph, dir;
K pk;
TreeNode<K, V> pl = p.left, pr = p.right, q;
if((ph = p.hash)>hash) {
p = pl;
} else if(ph<hash) {
p = pr;
} else if((pk = p.key) == key || (key != null && key.equals(pk))) {
return p;
} else if(pl == null) {
p = pr;
} else if(pr == null) {
p = pl;
} else if((kc != null || (kc = comparableClassFor(key)) != null)
&& (dir = compareComparables(kc, key, pk)) != 0) {
p = (dir<0) ? pl : pr;
} else if((q = pr.find(hash, key, kc)) != null) {
return q;
} else {
p = pl;
}
} while(p != null);
return null;
}
/**
* Calls find for root node.
*/
// 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null
final TreeNode<K, V> getTreeNode(int hash, Object key) {
return ((parent != null) ? root() : this).find(hash, key, null);
}
/**
* 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
*/
// 拆分红黑树以适应新的容量要求，因为扩容会导致index哈希槽处的那些元素进行再哈希，并最多分成两拨（bit为2的冪，一般传入的值是哈希数组旧容量）
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;
// 扩容后，元素e的位置不会改变（低区间）
if((e.hash & bit) == 0) {
if((e.prev = loTail) == null) {
loHead = e;
} else {
loTail.next = e;
}
loTail = e;
++lc;
// 扩容后，元素e会进入新的位置（高区间）
} else {
if((e.prev = hiTail) == null) {
hiHead = e;
} else {
hiTail.next = e;
}
hiTail = e;
++hc;
}
}
if(loHead != null) {
if(lc<=UNTREEIFY_THRESHOLD) {
// 遍历红黑树loHead上所有元素，创建一个链表
tab[index] = loHead.untreeify(map);
} else {
tab[index] = loHead;
if(hiHead != null) {
// 遍历loHead链表上的所有元素，创建一棵红黑树
loHead.treeify(tab);
}
// (else is already treeified)
}
}
if(hiHead != null) {
if(hc<=UNTREEIFY_THRESHOLD) {
// 遍历红黑树hiHead上所有元素，创建一个链表
tab[index + bit] = hiHead.untreeify(map);
} else {
tab[index + bit] = hiHead;
if(loHead != null) {
// 遍历hiHead链表上的所有元素，创建一棵红黑树
hiHead.treeify(tab);
}
}
}
}
/**
* 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;
}
return tr == null || checkInvariants(tr);
}
}
// HashMap中key的集合
final class KeySet extends AbstractSet<K> {
public final int size() {
return size;
}
public final boolean remove(Object key) {
return removeNode(hash(key), key, null, false, true) != null;
}
public final void clear() {
HashMap.this.clear();
}
public final boolean contains(Object o) {
return containsKey(o);
}
public final Iterator<K> iterator() {
return new KeyIterator();
}
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();
}
}
}
}
// HashMap中value的集合
final class Values extends AbstractCollection<V> {
public final int size() {
return size;
}
public final void clear() {
HashMap.this.clear();
}
public final boolean contains(Object o) {
return containsValue(o);
}
public final Iterator<V> iterator() {
return new ValueIterator();
}
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();
}
}
}
}
// HashMap中key-value的集合，Entry的本质就是Node
final class EntrySet extends AbstractSet<Map.Entry<K, V>> {
public final int size() {
return size;
}
public final void clear() {
HashMap.this.clear();
}
public final boolean contains(Object o) {
if(!(o instanceof Map.Entry)) {
return false;
}
Map.Entry<?, ?> e = (Map.Entry<?, ?>) o;
Object key = e.getKey();
// 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null
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 Iterator<Map.Entry<K, V>> iterator() {
return new EntryIterator();
}
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();
}
}
}
}
// HashMap迭代器
abstract class HashIterator {
// 当前正在处理元素
Node<K, V> next; // next entry to return
// 下次即将即将处理的元素
Node<K, V> current; // current entry
// 记录HashMap当前的修改次数，后续遍历时如果发现修改次数发生了变化，则返回失败信息
int expectedModCount; // for fast-fail
// 下一个待处理元素所在的哈希槽索引
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;
}
}
// key的迭代器
final class KeyIterator extends HashIterator implements Iterator<K> {
public final K next() {
return nextNode().key;
}
}
// value的迭代器
final class ValueIterator extends HashIterator implements Iterator<V> {
public final V next() {
return nextNode().value;
}
}
// key-value对的迭代器
final class EntryIterator extends HashIterator implements Iterator<Map.Entry<K, V>> {
public final Map.Entry<K, V> next() {
return nextNode();
}
}
// HashMap的可分割迭代器
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;
}
public final long estimateSize() {
getFence(); // force init
return (long) est;
}
// initialize fence and size on first use
final int getFence() {
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;
}
}
// key的可分割迭代器
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);
}
// 从容器的指定范围切割一段元素，将其打包到Spliterator后返回，特征值不变（这里会切割前一半元素出来）
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);
}
// 对容器中的单个当前元素执行择取操作
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;
}
// 遍历容器内每个元素，在其上执行相应的择取操作
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 int characteristics() {
return (fence<0 || est == map.size ? Spliterator.SIZED : 0) | Spliterator.DISTINCT;
}
}
// value的可分割迭代器
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);
}
// 从容器的指定范围切割一段元素，将其打包到Spliterator后返回，特征值不变（这里会切割前一半元素出来）
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);
}
// 对容器中的单个当前元素执行择取操作
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;
}
// 遍历容器内每个元素，在其上执行相应的择取操作
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 int characteristics() {
return (fence<0 || est == map.size ? Spliterator.SIZED : 0);
}
}
// key-value的可分割迭代器
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);
}
// 从容器的指定范围切割一段元素，将其打包到Spliterator后返回，特征值不变（这里会切割前一半元素出来）
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);
}
// 对容器中的单个当前元素执行择取操作
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;
}
// 遍历容器内每个元素，在其上执行相应的择取操作
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 int characteristics() {
return (fence<0 || est == map.size ? Spliterator.SIZED : 0) | Spliterator.DISTINCT;
}
}
}
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