HashMap
目录
-
- HashMap
- 目录
- 概述
- final变量
- 静态内部类
- 静态工具方法
- 成员变量
- 构造方法
- 成员方法
- 迭代器
- Spliterator
- Summary
概述
Map是一种 key-value 格式的数据结构, key唯一。
HashMap是Java Map接口的实现类， 实现了Map接口的所有方法， 而且允许key为null， value也为null。
HashMap与HashTable基本上就是一样的， 唯一的区别就是HashTable是线程安全的， 而HashMap不是(这跟ArrayList和Vector的区别是一样的)。
HashMap不保证map的顺序， key-value pair是”随机”的存放在map中的。
假定元素已经被hash函数均匀的分散在了一个个的桶(buckets)中， get()和put()的时间复杂度为O(1)。在集合上的迭代需要的时间为O(M + N)， 其中M是HashMap的capacity(桶的数目)， 而N是HashMap的size(key-value的数目)， 所以， 如果很在乎性能的话， 那么初始的capacity就不要设置的太大咯。
如果HashMap中的元素个数超过了capacity * loadfactor， 那么整个HashMap就会rebuilt， 一般loadfactor的值是0.75。
如图所示，当多个元素经过hash()后得到了同一个hash值，那么他们会被放入一个桶内，并初始以链表的形式存储，但是当元素数目达到一定得数量之后，链表就会被”树化”(treeify)成红黑树，提高搜索的性能。
同样， 关于synchronize和fast-fail就不赘述了， 跟ArrayList， LinkedList都是相似的。
final变量
// 所有的capacity的数值必须是2的整数次幂
static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; // aka 16
/**
* 最大capacity, 2^30
*/
static final int MAXIMUM_CAPACITY = 1 << 30;
/**
* 默认的，loadfactor
*/
static final float DEFAULT_LOAD_FACTOR = 0.75f;
/**
* 一般情况下，元素的hash值如果相同，那么就依次存在一个链表里
* 如果链表里的元素数目超过TREEIFY_THRESHOLD，就要把链表转化成一棵红黑树
*/
static final int TREEIFY_THRESHOLD = 8;
/**
* 与TREEIFY_THRESHOLD相对应，如果红黑树里的元素数目小于UNTREEIFY_THRESHOLD
* 红黑树就退化成一个链表
*/
static final int UNTREEIFY_THRESHOLD = 6;
/**
* 这个成员变量的定义是:
* 如果
* 1. 一个桶里的元素个数大于TREEIFY_THRESHOLD，且
* 2. HashTable的桶的个数大于MIN_TREEIFY_CAPACITY
* 那么，就对桶里的元素进行"树化"，否则
* 仅仅resize整个HashTable
*/
static final int MIN_TREEIFY_CAPACITY = 64;静态内部类
/**
* 桶里的元素(节点)，含有——key, value, next
* 所以整个桶里的元素构成了一个链表
*/
static class Node implements Map.Entry {
final int hash;
final K key;
V value;
Node next;
Node(int hash, K key, V value, Node 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;
}
// key与key相等，value与value相等，即可认为相等啦
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;
}
} 静态工具方法
static final int hash(Object key) {
int h;
return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
}
/**
* 如果x实现了comparable接口，那么返回x的类型
*/
static Class comparableClassFor(Object x) {
if (x instanceof Comparable) {
Class c; Type[] ts, as; Type t; ParameterizedType p;
if ((c = x.getClass()) == String.class) // bypass checks
return c;
if ((ts = c.getGenericInterfaces()) != null) {
for (int i = 0; i < ts.length; ++i) {
if (((t = ts[i]) 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;
}
/**
* kc是k的类型
*/
@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));
}
/**
* 返回不小于cap的最小的2的整次幂
* 比如
* return 8 if cap = 7,
* return 8 if cap = 8,
* return 16 if cap = 9,
*/
static final int tableSizeFor(int cap) {
int n = cap - 1; // 如果cap已经是2次幂整数了，这行能保证最后n不会超过cap
// 如果n >>> 1不为0，能保证n最高非0位连续2次，即0..011xxxxxxxx
n |= n >>> 1;
// 如果n >>> 2不为0，保证n最高非0位连续4次，即0..01111xxxxxx
n |= n >>> 2;
// 如果n >>> 4不为0，保证n最高非0位连续8次，即0..011111111xx
n |= n >>> 4;
// 如果n >>> 8不为0，保证n最高非0位连续16次，即0..0111..11xx(16个1)
n |= n >>> 8;
// 如果n >>> 16不为0，保证n最高非0位连续32次，即0..0111..11xx(32个1)
n |= n >>> 16;
return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
}
成员变量
/**
*
* hash表，长度总是2的幂次
*/
transient Node[] table;
/**
* key-value的集合
*/
transient Set> entrySet;
/**
* map里的key-value数目
*/
transient int size;
transient int modCount;
/**
* resize的门限值，超过值，就要resize了，值为(capacity * load factor)
* The next size value at which to resize (capacity * load factor).
*/
int threshold;
final float loadFactor; 构造方法
// initialCapacity会在内部做一个转换，转换成一个2次幂整数
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);
}
public HashMap(int initialCapacity) {
this(initialCapacity, DEFAULT_LOAD_FACTOR);
}
/**
* 啥都没指定，那么capacity就是INITIAL_CAPACITY(16)以及DEFAULT_LOAD_FACTOR(0.75)
*/
public HashMap() {
this.loadFactor = DEFAULT_LOAD_FACTOR; // all other fields defaulted
}
/**
* 从一个map中构造HashMap，容量要保证容纳m的所有元素
* loadfactor就是默认的0.75
*/
public HashMap(Map m) {
this.loadFactor = DEFAULT_LOAD_FACTOR;
putMapEntries(m, false);
}
成员方法
// 把m中的所有元素放到本HashMap中，evict参数hashMap用不着
final void putMapEntries(Map m, boolean evict) {
int s = m.size(); // 获取m中key-value的数目
if (s > 0) {
if (table == null) { // table为空，表名还没用呢
// 用m的大小除以loadfactor得到新的capacity，注意要加1哦
float ft = ((float)s / loadFactor) + 1.0F;
int t = ((ft < (float)MAXIMUM_CAPACITY) ?
(int)ft : MAXIMUM_CAPACITY);
if (t > threshold)
// 更新一下门限
threshold = tableSizeFor(t);
}
else if (s > threshold)
// 如果m的大小已经大于当前的门限了，就resize咯
resize();
// 遍历赋值
for (Map.Entry e : m.entrySet()) {
K key = e.getKey();
V value = e.getValue();
// 完成赋值，主要就是这个方法，重点关注下☆
putVal(hash(key), key, value, false, evict);
}
}
}
public int size() {
return size;
}
public boolean isEmpty() {
return size == 0;
}
/**
* 通过hash和key来获取值，无需赘述啦
*/
public V get(Object key) {
Node e;
return (e = getNode(hash(key), key)) == null ? null : e.value;
}
/**
* 通过hash和key来获取值
*/
final Node getNode(int hash, Object key) {
Node[] tab; Node first, e; int n; K k;
// (n - 1) & hash 这个就是桶的第一个元素的位置，也是链表的表头
if ((tab = table) != null && (n = tab.length) > 0 &&
(first = tab[(n - 1) & hash]) != null) {
if (first.hash == hash && // 总是检查表头
// key相同或者equals就返回first
((k = first.key) == key || (key != null && key.equals(k))))
return first;
// 否则，链表就往后走
if ((e = first.next) != null) {
// 如果链表已经被"树化"了，那么调用getTreeNode()
if (first instanceof TreeNode)
return ((TreeNode)first).getTreeNode(hash, key);
// 还是链表，那就一直next找
do {
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
return e;
} while ((e = e.next) != null);
}
}
return null;
}
/**
* 复用getNode()，如果返回不为空，则为包含这个key
*/
public boolean containsKey(Object key) {
return getNode(hash(key), key) != null;
}
/**
* 添加一对key-value，如果key已经存在了，就覆盖
*/
public V put(K key, V value) {
return putVal(hash(key), key, value, false, true);
}
/**
* 往HashMap中插值,先查找，再插入
* evict: 这个参数如果为true，那么每插入一个新值
* 就把链表头"踢出去"...，保持链表元素数目不变
*/
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
boolean evict) {
Node[] tab; Node p; int n, i;
if ((tab = table) == null || (n = tab.length) == 0)
n = (tab = resize()).length; // table为空，需要"扩容"
// (n - 1) & hash，n肯定是2的幂次方
// 这个表达式与 hash % (n - 1) 功能一样，但是更快
// 于是p就是桶中链表的头节点或者是桶中的树根
if ((p = tab[i = (n - 1) & hash]) == null)
// 为空，说明桶里还没有元素呢，加进去即可
tab[i] = newNode(hash, key, value, null);
else { // 说明桶里有元素，两种情况: 要么是链表，要么是树
Node e; K k;
if (p.hash == hash &&
((k = p.key) == key || (key != null && key.equals(k))))
e = p; // 就是头，不用再算了
else if (p instanceof TreeNode) // 是树
e = ((TreeNode)p).putTreeVal(this, tab, hash, key, value);
else {
// 是链表
for (int binCount = 0; ; ++binCount) {
if ((e = p.next) == null) { // 没找到，说明是要插入新的节点
p.next = newNode(hash, key, value, null);
if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
treeifyBin(tab, hash);// 插入导致链表变树
break;
}
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
break;
p = e;
}
}
// 旧值替换成新值
if (e != null) { // 说明新加的元素已经存在了，更新一下旧值
V oldValue = e.value;
if (!onlyIfAbsent || oldValue == null)
e.value = value;
afterNodeAccess(e);
return oldValue;
}
}
++modCount;
if (++size > threshold)
resize();
afterNodeInsertion(evict);
return null;
}
/**
* 扩容，要保持元素顺序不变，或者是以2的整数次幂移动
*/
final Node[] resize() {
Node[] oldTab = table;
int oldCap = (oldTab == null) ? 0 : oldTab.length;
int oldThr = threshold;
int newCap, newThr = 0;
if (oldCap > 0) {
if (oldCap >= MAXIMUM_CAPACITY) {
threshold = Integer.MAX_VALUE;
return oldTab; // 旧的HashMap已经够大了，没法扩容
}
// capacity扩大2倍，threshold扩大2倍(if possible)
else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&
oldCap >= DEFAULT_INITIAL_CAPACITY)
newThr = oldThr << 1; // double threshold
}
// 旧的HashMap的capacity为0
else if (oldThr > 0)
newCap = oldThr;
// 旧的capacity为0， 旧的threshold也为0，就用默认的咯
else {
newCap = DEFAULT_INITIAL_CAPACITY;
newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);
}
if (newThr == 0) {
float ft = (float)newCap * loadFactor;
newThr = (newCap < MAXIMUM_CAPACITY && ft < (float)MAXIMUM_CAPACITY ?
(int)ft : Integer.MAX_VALUE);
}
// 更新一下threshold属性
threshold = newThr;
@SuppressWarnings({"rawtypes","unchecked"})
Node[] newTab = (Node[])new Node[newCap];
table = newTab;
// 旧的HashMap如果是空，直接就结束吧
if (oldTab != null) {
for (int j = 0; j < oldCap; ++j) {
Node e; // e是HashMap中一个个桶中的首元素
if ((e = oldTab[j]) != null) {
oldTab[j] = null; // 原先的置空了
if (e.next == null) // 桶里就一个节点
newTab[e.hash & (newCap - 1)] = e;
else if (e instanceof TreeNode) // 桶里的元素构成了树
((TreeNode)e).split(this, newTab, j, oldCap);
else { // 桶里的节点构成了链表，记得要保证元素顺序
/**
* 举例说明一下即可，对于capacity为16的HashMap
* hash值为7和23的元素是放在一个桶里的，假设index为0和1
* 扩容后，长度变成了32，那么此时7和23就不在一个桶里了
* 7在编号为7的桶里，index为0
* 23在编号为23的桶里，index也为0
* loHead = 7[0], loTail = 7[0]
* hiHead = 23[0], hiTail = 23[0]
* 判断是Hi还是Low，拿hash值与原先的capacity(16)与一下即可
*/
Node loHead = null, loTail = null;
Node hiHead = null, hiTail = null;
Node next;
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;
}
/**
* 先把链表中的节点统统变成树里的节点，然后在进行treeify
*/
final void treeifyBin(Node[] tab, int hash) {
int n, index; Node e;
if (tab == null || (n = tab.length) < MIN_TREEIFY_CAPACITY)
resize();
else if ((e = tab[index = (n - 1) & hash]) != null) {
TreeNode hd = null, tl = null;
do {
TreeNode 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)
// 树化
hd.treeify(tab);
}
}
// 这个方法会替换掉已经存在的key-value
public void putAll(Map m) {
putMapEntries(m, true);
}
public V remove(Object key) {
Node e;
return (e = removeNode(hash(key), key, null, false, true)) == null ?
null : e.value;
}
// 先查找，再删除
final Node removeNode(int hash, Object key, Object value,
boolean matchValue, boolean movable) {
Node[] tab; Node p; int n, index;
if ((tab = table) != null && (n = tab.length) > 0 &&
(p = tab[index = (n - 1) & hash]) != null) {
Node 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)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);
}
}
if (node != null && (!matchValue || (v = node.value) == value ||
(value != null && value.equals(v)))) {
if (node instanceof TreeNode)
((TreeNode)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;
}
public void clear() {
Node[] tab;
modCount++;
if ((tab = table) != null && size > 0) {
size = 0;
for (int i = 0; i < tab.length; ++i)
tab[i] = null;
}
}
// 找的好辛苦
public boolean containsValue(Object value) {
Node[] tab; V v;
if ((tab = table) != null && size > 0) {
for (int i = 0; i < tab.length; ++i) {
for (Node e = tab[i]; e != null; e = e.next) {
if ((v = e.value) == value ||
(value != null && value.equals(v)))
return true;
}
}
}
return false;
}
/**
* 返回Map中的所有key的集合
*/
public Set keySet() {
Set ks;
return (ks = keySet) == null ? (keySet = new KeySet()) : ks;
}
// 由此也可以窥探到Set和Map的关系--Set就是Map，只不过没有用Map里的Value,把key当成Value
final class KeySet extends AbstractSet {
public final int size() { return size; }
public final void clear() { HashMap.this.clear(); }
public final Iterator 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 spliterator() {
return new KeySpliterator<>(HashMap.this, 0, -1, 0, 0);
}
public final void forEach(Consumersuper K> action) {
Node[] tab;
if (action == null)
throw new NullPointerException();
if (size > 0 && (tab = table) != null) {
int mc = modCount;
for (int i = 0; i < tab.length; ++i) {
for (Node e = tab[i]; e != null; e = e.next)
action.accept(e.key);
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
}
/**
* 返回Map中的全部values集合
*/
public Collection values() {
Collection vs;
return (vs = values) == null ? (values = new Values()) : vs;
}
// 注意到Values没有remove()方法，因为没有key，没法删
final class Values extends AbstractCollection {
public final int size() { return size; }
public final void clear() { HashMap.this.clear(); }
public final Iterator iterator() { return new ValueIterator(); }
public final boolean contains(Object o) { return containsValue(o); }
public final Spliterator spliterator() {
return new ValueSpliterator<>(HashMap.this, 0, -1, 0, 0);
}
public final void forEach(Consumersuper V> action) {
Node[] tab;
if (action == null)
throw new NullPointerException();
if (size > 0 && (tab = table) != null) {
int mc = modCount;
for (int i = 0; i < tab.length; ++i) {
for (Node e = tab[i]; e != null; e = e.next)
action.accept(e.value);
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
}
/**
* 返回Entry的集合，一个Entry是一个key-value的封装
*/
public Set> entrySet() {
Set> es;
return (es = entrySet) == null ? (entrySet = new EntrySet()) : es;
}
final class EntrySet extends AbstractSet> {
public final int size() { return size; }
public final void clear() { HashMap.this.clear(); }
public final Iterator> 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 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> spliterator() {
return new EntrySpliterator<>(HashMap.this, 0, -1, 0, 0);
}
public final void forEach(Consumersuper Map.Entry> action) {
Node[] tab;
if (action == null)
throw new NullPointerException();
if (size > 0 && (tab = table) != null) {
int mc = modCount;
for (int i = 0; i < tab.length; ++i) {
for (Node e = tab[i]; e != null; e = e.next)
action.accept(e);
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
}
// JDK8的方法
// 跟Python的get(para, default)是一样的
@Override
public V getOrDefault(Object key, V defaultValue) {
Node e;
return (e = getNode(hash(key), key)) == null ? defaultValue : e.value;
}
@Override
public V putIfAbsent(K key, V value) {
return putVal(hash(key), key, value, true, true);
}
@Override
public boolean remove(Object key, Object value) {
return removeNode(hash(key), key, value, true, true) != null;
}
@Override
public boolean replace(K key, V oldValue, V newValue) {
Node 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;
}
@Override
public V replace(K key, V value) {
Node e;
if ((e = getNode(hash(key), key)) != null) {
V oldValue = e.value;
e.value = value;
afterNodeAccess(e);
return oldValue;
}
return null;
}
// 如果key对应的元素不存在，那么就用mappingFunction算出一个value，插入Map
@Override
public V computeIfAbsent(K key,
Functionsuper K, ? extends V> mappingFunction) {
if (mappingFunction == null)
throw new NullPointerException();
int hash = hash(key);
Node[] tab; Node first; int n, i;
int binCount = 0;
TreeNode t = null;
Node 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)first).getTreeNode(hash, key);
else {
Node 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;
// 如果元素存在，且元素的value不为空，啥也不干
if (old != null && (oldValue = old.value) != null) {
afterNodeAccess(old);
return oldValue;
}
}
V v = mappingFunction.apply(key);
if (v == null) { // 算出一个null出来
return null;
} else if (old != null) { // 元素的value为空，更新，返回
old.value = v;
afterNodeAccess(old);
return v;
}
// v != null, old == null，且桶里的元素都是树节点，放在书中
else if (t != null)
t.putTreeVal(this, tab, hash, key, v);
else { // 放在链表中
tab[i] = newNode(hash, key, v, first);
if (binCount >= TREEIFY_THRESHOLD - 1) // 正好到了"树化"的数目...
treeifyBin(tab, hash);
}
++modCount;
++size;
afterNodeInsertion(true);
return v;
}
// key和value都不为空，再由一个有两个参数的函数映射成新的value，更新
public V computeIfPresent(K key,
BiFunctionsuper K, ? super V, ? extends V> remappingFunction) {
if (remappingFunction == null)
throw new NullPointerException();
Node e; V oldValue;
int hash = hash(key);
if ((e = getNode(hash, key)) != null &&
(oldValue = e.value) != null) {
V v = remappingFunction.apply(key, oldValue);
if (v != null) {
e.value = v;
afterNodeAccess(e);
return v;
}
else
removeNode(hash, key, null, false, true);
}
return null;
}
/**
* 如果key对应的元素old存在，根据remappingFunction(key, oldVal)映射出来的newVal
* 1. 如果不为空，更新old的oldVal为newVal
* 2. 为空，删除old节点
* 如果old不存在，且newVal不为空
* 1. old的hash值所在的桶里的元素为树节点，那么新建节点，插入tree中
* 2. 否则就插入到链表中
* 否则，就返回null吧
*/
@Override
public V compute(K key,
BiFunctionsuper K, ? super V, ? extends V> remappingFunction) {
if (remappingFunction == null)
throw new NullPointerException();
int hash = hash(key);
Node[] tab; Node first; int n, i;
int binCount = 0;
TreeNode t = null;
Node 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)first).getTreeNode(hash, key);
else {
Node 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;
V v = remappingFunction.apply(key, oldValue);
if (old != null) {
if (v != null) {
old.value = v;
afterNodeAccess(old);
}
else
removeNode(hash, key, null, false, true);
}
else if (v != null) {
if (t != null)
t.putTreeVal(this, tab, hash, key, v);
else {
tab[i] = newNode(hash, key, v, first);
if (binCount >= TREEIFY_THRESHOLD - 1)
treeifyBin(tab, hash);
}
++modCount;
++size;
afterNodeInsertion(true);
}
return v;
}
// 跟compute差不多，只不过新加了一个value参数
@Override
public V merge(K key, V value,
BiFunctionsuper V, ? super V, ? extends V> remappingFunction) {
if (value == null)
throw new NullPointerException();
if (remappingFunction == null)
throw new NullPointerException();
int hash = hash(key);
Node[] tab; Node first; int n, i;
int binCount = 0;
TreeNode t = null;
Node 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)first).getTreeNode(hash, key);
else {
Node 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);
}
}
if (old != null) {
V v;
if (old.value != null)
v = remappingFunction.apply(old.value, value);
else
v = value;
if (v != null) {
old.value = v;
afterNodeAccess(old);
}
else
removeNode(hash, key, null, false, true);
return v;
}
if (value != null) {
if (t != null)
t.putTreeVal(this, tab, hash, key, value);
else {
tab[i] = newNode(hash, key, value, first);
if (binCount >= TREEIFY_THRESHOLD - 1)
treeifyBin(tab, hash);
}
++modCount;
++size;
afterNodeInsertion(true);
}
return value;
}
@Override
public void forEach(BiConsumersuper K, ? super V> action) {
Node[] tab;
if (action == null)
throw new NullPointerException();
if (size > 0 && (tab = table) != null) {
int mc = modCount;
for (int i = 0; i < tab.length; ++i) {
for (Node e = tab[i]; e != null; e = e.next)
action.accept(e.key, e.value);
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
// 把元素的value替换成一个function(key, value)的输出值
@Override
public void replaceAll(BiFunctionsuper K, ? super V, ? extends V> function) {
Node[] tab;
if (function == null)
throw new NullPointerException();
if (size > 0 && (tab = table) != null) {
int mc = modCount;
for (int i = 0; i < tab.length; ++i) {
for (Node e = tab[i]; e != null; e = e.next) {
e.value = function.apply(e.key, e.value);
}
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
/* ------------------------------------------------------------ */
// 下一是浅拷贝和序列化的操作...
// Cloning and serialization
/**
* Returns a shallow copy of this HashMap instance: the keys and
* values themselves are not cloned.
*
* @return a shallow copy of this map
*/
@SuppressWarnings("unchecked")
@Override
public Object clone() {
HashMap result;
try {
result = (HashMap)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;
}
/**
* Save the state of the HashMap instance to a stream (i.e.,
* serialize it).
*
* @serialData The capacity of the HashMap (the length of the
* bucket array) is emitted (int), followed by the
* size (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);
}
/**
* Reconstitute the {@code HashMap} instance from a stream (i.e.,
* deserialize it).
*/
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);
@SuppressWarnings({"rawtypes","unchecked"})
Node[] tab = (Node[])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);
}
}
} 迭代器
abstract class HashIterator {
Node next; // next entry to return
Node current; // current entry
int expectedModCount; // for fast-fail
int index; // current slot
HashIterator() {
expectedModCount = modCount;
Node[] t = table;
current = next = null;
index = 0;
if (t != null && size > 0) { 指向第一个entry
do {} while (index < t.length && (next = t[index++]) == null);
}
}
public final boolean hasNext() {
return next != null;
}
final Node nextNode() {
Node[] t;
Node 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 p = current;
if (p == null)
throw new IllegalStateException();
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
current = null;
K key = p.key;
removeNode(hash(key), key, null, false, false);
expectedModCount = modCount;
}
}
final class KeyIterator extends HashIterator
implements Iterator {
public final K next() { return nextNode().key; }
}
final class ValueIterator extends HashIterator
implements Iterator {
public final V next() { return nextNode().value; }
}
final class EntryIterator extends HashIterator
implements Iterator> {
public final Map.Entry next() { return nextNode(); }
} Spliterator
基本上桶ArrayList和LinkedList的用法是一样的，一个研究好了，一劳永逸
static class HashMapSpliterator {
final HashMap map;
Node 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 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 m = map;
est = m.size;
expectedModCount = m.modCount;
Node[] 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
extends HashMapSpliterator
implements Spliterator {
KeySpliterator(HashMap m, int origin, int fence, int est,
int expectedModCount) {
super(m, origin, fence, est, expectedModCount);
}
public KeySpliterator 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(Consumersuper K> action) {
int i, hi, mc;
if (action == null)
throw new NullPointerException();
HashMap m = map;
Node[] 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 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(Consumersuper K> action) {
int hi;
if (action == null)
throw new NullPointerException();
Node[] 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
extends HashMapSpliterator
implements Spliterator {
ValueSpliterator(HashMap m, int origin, int fence, int est,
int expectedModCount) {
super(m, origin, fence, est, expectedModCount);
}
public ValueSpliterator 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(Consumersuper V> action) {
int i, hi, mc;
if (action == null)
throw new NullPointerException();
HashMap m = map;
Node[] 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 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(Consumersuper V> action) {
int hi;
if (action == null)
throw new NullPointerException();
Node[] 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
extends HashMapSpliterator
implements Spliterator> {
EntrySpliterator(HashMap m, int origin, int fence, int est,
int expectedModCount) {
super(m, origin, fence, est, expectedModCount);
}
public EntrySpliterator 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(Consumersuper Map.Entry> action) {
int i, hi, mc;
if (action == null)
throw new NullPointerException();
HashMap m = map;
Node[] 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 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(Consumersuper Map.Entry> action) {
int hi;
if (action == null)
throw new NullPointerException();
Node[] 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 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;
}
}
/* ------------------------------ */
/**
* 在后面就是一些红黑树的操作...
* / Summary
hash值与(length - 1)的与(&)操作之后，其实功能与(hash % n - 1)的作用是一样的，但是更快
- 如果桶里有多个元素，那么这个位置就是整个链表的表头。
- 如果桶中元素个数超过TREEIFY_THRESHOLD，那么链表就会”树化”为红黑树
HashMap查找操作
HashMap中元素的查找，遵循以下步骤:- 先根据key得到hash值hash(key -> hash)
- 再根据hash得到HashMap中桶的位置，也就是相同hash值对应的首个节点(hash -> first)
- 判断key与first是否相等(必要的时候也会判断值是否相等)
- 相等，则返回，否则
- 判断first是不是TreeNode，是，则转化为在树中查找元素；否则
- 桶里的元素肯定构成了一个链表，按照链表的方式查找即可
- 查找成功，返回节点，否则，返回null。
HashMap中桶的元素超过一定数目之后会转化成 红黑 树!!! 比较复杂，有精力可以看看。