前面已经学习了List的实现类并做了总结，今天开始学习HashMap源码。参考的JDK版本为1.8。
相信大家对HashMap的使用已经很熟悉了，它和List的最大的不同是它是以key-value的形式存储数据的。HashMap是如何保存和处理key-value键值对的？本文将分析HashMap的内部结构及实现原理，帮助大家更好的使用它。
HashMap数据结构
在分析HashMap源码之前，有必要了解HashMap的数据结构，否则很难理解下面的内容。
![MarkdownPhotos/master/CSDNBlogs/container/HashMap/HashMapDateStructure.jpg]()
从上图中可以很清楚的看到，HashMap的数据结构是数组+链表+红黑树（红黑树since JDK1.8）。常把数组中的每一个节点称为一个桶。当向桶中添加一个key-value时，首先计算元素key的hash值，以此确定插入数组中的位置，但是可能存在同一hash值的元素已经被放在数组同一位置了，这种现象称为碰撞，这时按照尾插法(jdk1.7及以前为头插法)的方式添加key-value到同一hash值的元素的后面，形成了链表。当链表长度超过8(TREEIFY_THRESHOLD)时，链表就转换为红黑树。
部分顶部注释
Hash table based implementation of the Map interface. This implementation provides all of the optional map operations, and permits null values and the null key. (The HashMap class is roughly equivalent to HashMap , except that it is unsynchronized and permits nulls.) This class makes no guarantees as to the order of the map; in particular, it does not guarantee that the order will remain constant over time.
HashMap是Map接口基于哈希表的实现。这种实现提供了所有可选的Map操作，允许key和value为null。HashMap大致和HashTable相同，除了HashMap是unsynchronized的，而且它允许key和value为null。
This implementation provides constant-time performance for the basic operations (get and put), assuming the hash function disperses the elements properly among the buckets. Iteration over collection views requires time proportional to the “capacity” of the HashMap instance (the number of buckets) plus its size (the number of key-value mappings). Thus, it’s very important not to set the initial capacity too high (or the load factor too low) if iteration performance is important.
这个实现为基本实现(get and put)提供了稳定的性能，假设哈希函数在桶内正确分散元素。如果遍历操作很重要，就不要把capacity设置得太高（或load factor设置得太低），否则会严重降低遍历的效率。
An instance of HashMap has two parameters that affect its performance: initial capacity and load factor. The capacity is the number of buckets in the hash table, and the initial capacity is simply the capacity at the time the hash table is created. The load factor is a measure of how full the hash table is allowed to get before its capacity is automatically increased. When the number of entries in the hash table exceeds the product of the load factor and the current capacity, the hash table is rehashed (that is, internal data structures are rebuilt) so that the hash table has approximately twice the number of buckets.
HashMap有两个影响性能的重要参数：初始化容量initial capacity、负载因子load factor。initial capacity*load factor就是当前允许的最大元素数目，超过initial capacity*load factor之后，HashMap就会进行rehashed操作来进行扩容，扩容后的的容量为之前的两倍。
下面还有很长，不翻了。
HashMap层次结构图
先来看看ArrayList的定义：
public class HashMap<K,V> extends AbstractMap<K,V> implements Map<K,V>, Cloneable, Serializable
从中我们可以了解到：
- HashMap<K,V>：HashMap是以key-value形式存储数据的
- extends AbstractMap<K,V>：继承了AbstractMap，实现Map接口时需要实现的工作量大大减少了。
- implements Map<K,V>：实现了Map，实现了Map中声明的操作和default方法。
- implements Cloneable：表明其可以调用clone()方法来返回实例的field-for-field拷贝。
- implements Serializable：表明该类是可以序列化的。
建议大家以后查看一个类的继承实现关系的时候，使用类结构层次图。
![MarkdownPhotos/master/CSDNBlogs/container/HashMap/HashMapTH.jpg]()
如何查看类层次结构图可以参考我写过的一篇文章：
eclipse-查看继承层次图/继承实现层次图
静态全局变量
/**
* 默认初始化容量，值为16
* 必须是2的n次幂.
*/
static final int DEFAULT_INITIAL_CAPACITY = 1 << 4;
/**
* 最大容量, 如果一个更大的值在构造函数总被指定，将被MAXIMUM_CAPACITY 替换.
* 必须是2的倍数。最大容量为1<<30，即2的30次方。
*/
static final int MAXIMUM_CAPACITY = 1 << 30;
/**
* 默认的负载因子。
*/
static final float DEFAULT_LOAD_FACTOR = 0.75f;
/**
* 使用树形结构而不是链式结构临界值。
* 当添加一个元素被添加到有至少TREEIFY_THRESHOLD个节点的桶中，桶将被转化为树形结构。
* 临界值最小为8
*/
static final int TREEIFY_THRESHOLD = 8;
/**
* 恢复成链式结构的桶大小临界值
* 小于TREEIFY_THRESHOLD，临界值最大为6
*/
static final int UNTREEIFY_THRESHOLD = 6;
/**
* 桶可能被转化为树形结构的最小容量。当哈希表的大小超过这个阈值，才会把链式结构转化成树型结构，否则仅采取扩容来尝试减少冲突。
* 应该至少4*TREEIFY_THRESHOLD来避免扩容和树形结构化之间的冲突。
*/
static final int MIN_TREEIFY_CAPACITY = 64;
静态内部类Node
/**
* HashMap的节点类型。既是HashMap底层数组的组成元素，又是每个单向链表的组成元素
*/
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 String toString() { return key + "=" + value; }
public final int hashCode() {
return Objects.hashCode(key) ^ Objects.hashCode(value);
}
public final V setValue(V newValue) {
V oldValue = value;
value = newValue;
return oldValue;
}
public final boolean equals(Object o) {
if (o == this)
return true;
if (o instanceof Map.Entry) {
Map.Entry<?,?> e = (Map.Entry<?,?>)o;
if (Objects.equals(key, e.getKey()) &&
Objects.equals(value, e.getValue()))
return true;
}
return false;
}
}
静态公用方法
hash( Object key)
不管增加、删除、查找键值对，定位到哈希桶数组的位置都是很关键的第一步。计算位置的方法如下
(n - 1) & hash
其中的n为数组的长度，hash为hash(key)计算得到的值。
/**
* 计算key的哈希值。
*/
static final int hash(Object key) {
int h;
return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
}
从代码中可以看到，计算位置分为三步，第一步，取key的hashCode，第二步，key的hashCode高16位异或低16位，第三步，取模运算。
![MarkdownPhotos/master/CSDNBlogs/container/HashMap/hashFunc.jpg]()
看到这里有个疑问，为什么要做异或运算？
设想一下，如果n很小，假设为16的话，那么n-1即为15（0000 0000 0000 0000 0000 0000 0000 1111），这样的值如果跟hashCode()直接做与操作，实际上只使用了哈希值的后4位。如果当哈希值的高位变化很大，低位变化很小，这样很容易造成碰撞，所以把高低位都参与到计算中，从而解决了这个问题，而且也不会有太大的开销。
comparableClassFor( Object x)
/**
* 如果参数x实现了Comparable接口，返回参数x的类名，否则返回null
*/
static Class<?> comparableClassFor(Object x) {
if (x instanceof Comparable) {
Class<?> c; Type[] ts, as; Type t; ParameterizedType p;
if ((c = x.getClass()) == String.class)
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)
return c;
}
}
}
return null;
}
compareComparables( Class<?> kc, Object k, Object x)
/**
* 如果x的类型为kc，则返回k.compareTo(x)，否则返回0.
*/
@SuppressWarnings({"rawtypes","unchecked"})
static int compareComparables(Class<?> kc, Object k, Object x) {
return (x == null || x.getClass() != kc ? 0 :
((Comparable)k).compareTo(x));
}
tableSizeFor( int cap)
/**
* 返回大于等于cap的最小的二次幂数值。
*/
static final int tableSizeFor(int cap) {
int n = cap - 1;
n |= n >>> 1;
n |= n >>> 2;
n |= n >>> 4;
n |= n >>> 8;
n |= n >>> 16;
return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
}
域
/**
* 存储键值对的数组，一般是2的幂
*/
transient Node<K,V>[] table;
/**
* 键值对缓存，它们的映射关系集合保存在entrySet中。即使Key在外部修改导致hashCode变化，缓存中还可以找到映射关系
*/
transient Set<Map.Entry<K,V>> entrySet;
/**
* 键值对的实际个数
*/
transient int size;
/**
* 记录HashMap被修改结构的次数。
* 修改包括改变键值对的个数或者修改内部结构，比如rehash
* 这个域被用作HashMap的迭代器的fail-fast机制中（参考ConcurrentModificationException）
*/
transient int modCount;
/**
* 扩容的临界值，通过capacity * load factor可以计算出来。超过这个值HashMap将进行扩容
* @serial
*/
int threshold;
/**
* 负载因子
*
* @serial
*/
final float loadFactor;
构造函数
HashMap( int initialCapacity, float loadFactor)
/**
* 使用指定的初始化容量initial capacity 和负载因子load factor构造一个空HashMap
*
* @param initialCapacity 初始化容量
* @param loadFactor 负载因子
* @throws IllegalArgumentException 如果指定的初始化容量为负数或者加载因子为非正数。
*/
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);
}
HashMap( int initialCapacity)
/**
* 使用指定的初始化容量initial capacity和默认负载因子DEFAULT_LOAD_FACTOR（0.75）构造一个空HashMap
*
* @param initialCapacity 初始化容量
* @throws IllegalArgumentException 如果指定的初始化容量为负数
*/
public HashMap(int initialCapacity) {
this(initialCapacity, DEFAULT_LOAD_FACTOR);
}
HashMap()
/**
* 使用指定的初始化容量（16）和默认负载因子DEFAULT_LOAD_FACTOR（0.75）构造一个空HashMap
*/
public HashMap() {
this.loadFactor = DEFAULT_LOAD_FACTOR;
}
HashMap( Map<? extends K, ? extends V>m)
/**
* 使用指定Map m构造新的HashMap。使用指定的初始化容量（16）和默认负载因子DEFAULT_LOAD_FACTOR（0.75）
* @param m 指定的map
* @throws NullPointerException 如果指定的map是null
*/
public HashMap(Map<? extends K, ? extends V> m) {
this.loadFactor = DEFAULT_LOAD_FACTOR;
putMapEntries(m, false);
}
常用方法
putMapEntries(Map<? extends K, ? extends V> m, boolean evict)
/**
* Map.putAll and Map constructor的实现需要的方法。
* 将m的键值对插入本map中
*
* @param m the map
* @param evict 初始化map时使用false，否则使用true
*/
final void putMapEntries(Map<? extends K, ? extends V> m, boolean evict) {
int s = m.size();
if (s > 0) {
if (table == null) {
float ft = ((float)s / loadFactor) + 1.0F;
int t = ((ft < (float)MAXIMUM_CAPACITY) ?
(int)ft : MAXIMUM_CAPACITY);
if (t > threshold)
threshold = tableSizeFor(t);
}
else if (s > threshold)
resize();
for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) {
K key = e.getKey();
V value = e.getValue();
putVal(hash(key), key, value, false, evict);
}
}
}
size()
/**
* 返回map中键值对映射的个数
*
* @return map中键值对映射的个数
*/
public int size() {
return size;
}
isEmpty()
/**
* 如果map中没有键值对映射，返回true
*
* @return <如果map中没有键值对映射，返回true
*/
public boolean isEmpty() {
return size == 0;
}
get( Object key)
/**
* 返回指定的key对应的value，如果value为null，则返回null
*
* @see #put(Object, Object)
*/
public V get(Object key) {
Node<K,V> e;
return (e = getNode(hash(key), key)) == null ? null : e.value;
}
getNode( int hash, Object key)
/**
* 根据key的哈希值和key获取对应的节点
*
* @param hash 指定参数key的哈希值
* @param key 指定参数key
* @return 返回node，如果没有则返回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) {
if (first.hash == hash &&
((k = first.key) == key || (key != null && key.equals(k))))
return first;
if ((e = first.next) != null) {
if (first instanceof TreeNode)
return ((TreeNode<K,V>)first).getTreeNode(hash, key);
do {
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
return e;
} while ((e = e.next) != null);
}
}
return null;
}
containsKey( Object key)
/**
* 如果map中含有key为指定参数key的键值对，返回true
*
* @param key 指定参数key
* @return 如果map中含有key为指定参数key的键值对，返回true
*/
public boolean containsKey(Object key) {
return getNode(hash(key), key) != null;
}
put( K key, V value)
/**
* 将指定参数key和指定参数value插入map中，如果key已经存在，那就替换key对应的value
*
* @param key 指定key
* @param value 指定value
* @return 如果value被替换，则返回旧的value，否则返回null。当然，可能key对应的value就是null。
*/
public V put(K key, V value) {
return putVal(hash(key), key, value, false, true);
}
putVal( int hash, K key, V value, boolean onlyIfAbsent,boolean evict)
/**
* Map.put和其他相关方法的实现需要的方法
*
* @param hash 指定参数key的哈希值
* @param key 指定参数key
* @param value 指定参数value
* @param onlyIfAbsent 如果为true，即使指定参数key在map中已经存在，也不会替换value
* @param evict 如果为false，数组table在创建模式中
* @return 如果value被替换，则返回旧的value，否则返回null。当然，可能key对应的value就是null。
*/
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,boolean evict) {
Node<K,V>[] tab; Node<K,V> p; int n, i;
if ((tab = table) == null || (n = tab.length) == 0)
n = (tab = resize()).length;
if ((p = tab[i = (n - 1) & hash]) == null)
tab[i] = newNode(hash, key, value, null);
else {
Node<K,V> e; K k;
if (p.hash == hash &&
((k = p.key) == key || (key != null && key.equals(k))))
e = p;
else if (p instanceof TreeNode)
e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
else {
for (int binCount = 0; ; ++binCount) {
if ((e = p.next) == null) {
p.next = newNode(hash, key, value, null);
if (binCount >= TREEIFY_THRESHOLD - 1)
treeifyBin(tab, hash);
break;
}
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
break;
p = e;
}
}
if (e != null) {
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resize()
向hashMap对象里不停的添加元素，而HashMap对象内部的数组无法装载更多的元素时，hashMap就需要扩大数组的长度，以便能装入更多的元素。当然数组是无法自动扩容的，扩容方法使用一个新的数组代替已有的容量小的数组。
/**
* 对hashMap的数组table进行初始化或者扩容。
* 如果table为null，则对table进行初始化，否则，因为我们正在使用2的幂的扩容，桶中的元素必须待在原本的位置，或者移动2的幂的位置。
* @return 返回数组table
*/
final Node<K,V>[] resize() {
Node<K,V>[] 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;
}
else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&oldCap >= DEFAULT_INITIAL_CAPACITY)
newThr = oldThr << 1;
}
else if (oldThr > 0)
newCap = oldThr;
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);
}
threshold = newThr;
@SuppressWarnings({"rawtypes","unchecked"})
Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];
table = newTab;
if (oldTab != null) {
for (int j = 0; j < oldCap; ++j) {
Node<K,V> e;
if ((e = oldTab[j]) != null) {
oldTab[j] = null;
if (e.next == null)
newTab[e.hash & (newCap - 1)] = e;
else if (e instanceof TreeNode)
((TreeNode<K,V>)e).split(this, newTab, j, oldCap);
else {
Node<K,V> loHead = null, loTail = null;
Node<K,V> hiHead = null, hiTail = null;
Node<K,V> 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;
}
从代码中可以看到，扩容很耗性能。所以在使用HashMap的时候，先估算map的大小，初始化的时候给一个大致的数值，避免map进行频繁的扩容。
treeifyBin( Node<K,V>[] tab, int hash)
/**
* 将链表转化为红黑树
*/
final void treeifyBin(Node<K,V>[] tab, int hash) {
int n, index; Node<K,V> e;
if (tab == null || (n = tab.length) < MIN_TREEIFY_CAPACITY)
resize();
else if ((e = tab[index = (n - 1) & hash]) != null) {
TreeNode<K,V> hd = null, tl = null;
do {
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)
hd.treeify(tab);
}
}
putAll( Map<? extends K, ? extends V> m)
/**
* 将参数map中的所有键值对映射插入到hashMap中，如果有碰撞，则覆盖value。
* @param m 参数map
* @throws NullPointerException 如果map为null
*/
public void putAll(Map<? extends K, ? extends V> m) {
putMapEntries(m, true);
}
remove( Object key)
/**
* 删除hashMap中key为参数key的键值对
*
* @param key 参数key
* @return 如果没有对应的键值对，返回null，否则返回对应的value。
*/
public V remove(Object key) {
Node<K,V> e;
return (e = removeNode(hash(key), key, null, false, true)) == null ?
null : e.value;
}
removeNode( int hash, Object key, Object value,boolean matchValue, boolean movable)
/**
* Map.remove和相关方法的实现需要的方法
* 删除node
*
* @param hash key的哈希值
* @param key 参数key
* @param value 如果matchValue为true，则value也作为确定被删除的node的条件之一，否则忽略
* @param matchValue 如果为true，则value也作为确定被删除的node的条件之一
* @param movable 如果为false，删除node时不会删除其他node
* @return 返回被删除的node，如果没有node被删除，则返回null
*/
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;
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);
}
}
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;
}
clear()
/**
* 删除map中所有的键值对
*/
public void clear() {
Node<K,V>[] tab;
modCount++;
if ((tab = table) != null && size > 0) {
size = 0;
for (int i = 0; i < tab.length; ++i)
tab[i] = null;
}
}
containsValue( Object value)
/**
* 如果hashMap中的键值对有一对或多对的value为参数value，返回true
*
* @param value 参数value
* @return 如果hashMap中的键值对有一对或多对的value为参数value，返回true
*/
public boolean containsValue(Object value) {
Node<K,V>[] tab; V v;
if ((tab = table) != null && size > 0) {
for (int i = 0; i < tab.length; ++i) {
for (Node<K,V> e = tab[i]; e != null; e = e.next) {
if ((v = e.value) == value ||
(value != null && value.equals(v)))
return true;
}
}
}
return false;
}
keySet()
/**
* 返回hashMap中所有key的视图。
* 改变hashMap会影响到set，反之亦然。
* 如果当迭代器迭代set时，hashMap被修改(除非是迭代器自己的remove()方法)，迭代器的结果是不确定的。
* set支持元素的删除，通过Iterator.remove、Set.remove、removeAll、retainAll、clear操作删除hashMap中对应的键值对。不支持add和addAll方法。
*
* @return 返回hashMap中所有key的set视图
*/
public Set<K> keySet() {
Set<K> ks = keySet;
if (ks == null) {
ks = new KeySet();
keySet = ks;
}
return ks;
}
/**
* 内部类KeySet
*/
final class KeySet extends AbstractSet<K> {
public final int size() { return size; }
public final void clear() { HashMap.this.clear(); }
public final Iterator<K> iterator() { return new KeyIterator(); }
public final boolean contains(Object o) { return containsKey(o); }
public final boolean remove(Object key) {
return removeNode(hash(key), key, null, false, true) != null;
}
public final Spliterator<K> spliterator() {
return new KeySpliterator<>(HashMap.this, 0, -1, 0, 0);
}
public final void forEach(Consumer<? super K> action) {
Node<K,V>[] tab;
if (action == null)
throw new NullPointerException();
if (size > 0 && (tab = table) != null) {
int mc = modCount;
for (int i = 0; i < tab.length; ++i) {
for (Node<K,V> e = tab[i]; e != null; e = e.next)
action.accept(e.key);
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
}
values()
/**
* 返回hashMap中所有value的collection视图
* 改变hashMap会改变collection，反之亦然。
* 如果当迭代器迭代collection时，hashMap被修改（除非是迭代器自己的remove()方法），迭代器的结果是不确定的。
* collection支持元素的删除，通过Iterator.remove、Collection.remove、removeAll、retainAll、clear操作删除hashMap中对应的键值对。不支持add和addAll方法。
*
* @return 返回hashMap中所有key的collection视图
*/
public Collection<V> values() {
Collection<V> vs = values;
if (vs == null) {
vs = new Values();
values = vs;
}
return vs;
}
/**
* 内部类Values
*/
final class Values extends AbstractCollection<V> {
public final int size() { return size; }
public final void clear() { HashMap.this.clear(); }
public final Iterator<V> iterator() { return new ValueIterator(); }
public final boolean contains(Object o) { return containsValue(o); }
public final Spliterator<V> spliterator() {
return new ValueSpliterator<>(HashMap.this, 0, -1, 0, 0);
}
public final void forEach(Consumer<? super V> action) {
Node<K,V>[] tab;
if (action == null)
throw new NullPointerException();
if (size > 0 && (tab = table) != null) {
int mc = modCount;
for (int i = 0; i < tab.length; ++i) {
for (Node<K,V> e = tab[i]; e != null; e = e.next)
action.accept(e.value);
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
}
entrySet()
/**
* 返回hashMap中所有键值对的set视图
* 改变hashMap会影响到set，反之亦然。
* 如果当迭代器迭代set时，hashMap被修改(除非是迭代器自己的remove()方法)，迭代器的结果是不确定的。
* set支持元素的删除，通过Iterator.remove、Set.remove、removeAll、retainAll、clear操作删除hashMap中对应的键值对。不支持add和addAll方法。
*
* @return 返回hashMap中所有键值对的set视图
*/
public Set<Map.Entry<K,V>> entrySet() {
Set<Map.Entry<K,V>> es;
return (es = entrySet) == null ? (entrySet = new EntrySet()) : es;
}
/**
* 内部类EntrySet
*/
final class EntrySet extends AbstractSet<Map.Entry<K,V>> {
public final int size() { return size; }
public final void clear() { HashMap.this.clear(); }
public final Iterator<Map.Entry<K,V>> iterator() {
return new EntryIterator();
}
public final boolean contains(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry<?,?> e = (Map.Entry<?,?>) o;
Object key = e.getKey();
Node<K,V> candidate = getNode(hash(key), key);
return candidate != null && candidate.equals(e);
}
public final boolean remove(Object o) {
if (o instanceof Map.Entry) {
Map.Entry<?,?> e = (Map.Entry<?,?>) o;
Object key = e.getKey();
Object value = e.getValue();
return removeNode(hash(key), key, value, true, true) != null;
}
return false;
}
public final Spliterator<Map.Entry<K,V>> spliterator() {
return new EntrySpliterator<>(HashMap.this, 0, -1, 0, 0);
}
public final void forEach(Consumer<? super Map.Entry<K,V>> action) {
Node<K,V>[] tab;
if (action == null)
throw new NullPointerException();
if (size > 0 && (tab = table) != null) {
int mc = modCount;
for (int i = 0; i < tab.length; ++i) {
for (Node<K,V> e = tab[i]; e != null; e = e.next)
action.accept(e);
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
}
JDK8重写的方法
// Overrides of JDK8 Map extension methods
getOrDefault( Object key, V defaultValue)
/**
* 通过key映射到对应node，如果没映射到则返回默认值defaultValue
*
* @return key映射到对应的node，如果没映射到则返回默认值defaultValue
*/
@Override
public V getOrDefault(Object key, V defaultValue) {
Node<K,V> e;
return (e = getNode(hash(key), key)) == null ? defaultValue : e.value;
}
putIfAbsent( K key, V value)
/**
* 在hashMap中插入参数key和value组成的键值对，如果key在hashMap中已经存在，不替换value
*
* @return 如果key在hashMap中不存在，返回旧value
*/
@Override
public V putIfAbsent(K key, V value) {
return putVal(hash(key), key, value, true, true);
}
remove( Object key, Object value)
/**
* 删除hashMap中key为参数key，value为参数value的键值对。如果桶中结构为树，则级联删除
*
* @return 删除成功，返回true
*/
@Override
public boolean remove(Object key, Object value) {
return removeNode(hash(key), key, value, true, true) != null;
}
replace( K key, V oldValue, V newValue)
/**
* 使用newValue替换key和oldValue映射到的键值对中的value
*
* @return 替换成功，返回true
*/
@Override
public boolean replace(K key, V oldValue, V newValue) {
Node<K,V> e; V v;
if ((e = getNode(hash(key), key)) != null &&
((v = e.value) == oldValue || (v != null && v.equals(oldValue)))) {
e.value = newValue;
afterNodeAccess(e);
return true;
}
return false;
}
replace( K key, V value)
/**
* 使用参数value替换key映射到的键值对中的value
*
* @return 替换成功，返回true
*/
@Override
public V replace(K key, V value) {
Node<K,V> e;
if ((e = getNode(hash(key), key)) != null) {
V oldValue = e.value;
e.value = value;
afterNodeAccess(e);
return oldValue;
}
return null;
}
computeIfAbsent( K key,Function<? super K, ? extends V> mappingFunction)
/**
* 待补充
*
* @return
*/
@Override
public V computeIfAbsent(K key,Function<? super K, ? extends V> mappingFunction) {
if (mappingFunction == null)
throw new NullPointerException();
int hash = hash(key);
Node<K,V>[] tab; Node<K,V> first; int n, i;
int binCount = 0;
TreeNode<K,V> t = null;
Node<K,V> old = null;
if (size > threshold || (tab = table) == null ||
(n = tab.length) == 0)
n = (tab = resize()).length;
if ((first = tab[i = (n - 1) & hash]) != null) {
if (first instanceof TreeNode)
old = (t = (TreeNode<K,V>)first).getTreeNode(hash, key);
else {
Node<K,V> e = first; K k;
do {
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k)))) {
old = e;
break;
}
++binCount;
} while ((e = e.next) != null);
}
V oldValue;
if (old != null && (oldValue = old.value) != null) {
afterNodeAccess(old);
return oldValue;
}
}
V v = mappingFunction.apply(key);
if (v == null) {
return null;
} else if (old != null) {
old.value = v;
afterNodeAccess(old);
return v;
}
else 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;
}
computeIfPresent( K key,BiFunction<? super K, ? super V, ? extends V> remappingFunction)
/**
* 待补充
*
* @return
*/
public V computeIfPresent(K key,BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
if (remappingFunction == null)
throw new NullPointerException();
Node<K,V> e; V oldValue;
int hash = hash(key);
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;
}
compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction)
/**
* 待补充
*/
@Override
public V compute( K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
if (remappingFunction == null)
throw new NullPointerException();
int hash = hash(key);
Node<K,V>[] tab; Node<K,V> first; int n, i;
int binCount = 0;
TreeNode<K,V> t = null;
Node<K,V> old = null;
if (size > threshold || (tab = table) == null ||
(n = tab.length) == 0)
n = (tab = resize()).length;
if ((first = tab[i = (n - 1) & hash]) != null) {
if (first instanceof TreeNode)
old = (t = (TreeNode<K,V>)first).getTreeNode(hash, key);
else {
Node<K,V> e = first; K k;
do {
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k)))) {
old = e;
break;
}
++binCount;
} while ((e = e.next) != null);
}
}
V oldValue = (old == null) ? null : old.value;
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;
}
merge( K key, V value,BiFunction<? super V, ? super V, ? extends V> remappingFunction)
/**
* 待补充
*/
@Override
public V merge(K key, V value,BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
if (value == null)
throw new NullPointerException();
if (remappingFunction == null)
throw new NullPointerException();
int hash = hash(key);
Node<K,V>[] tab; Node<K,V> first; int n, i;
int binCount = 0;
TreeNode<K,V> t = null;
Node<K,V> old = null;
if (size > threshold || (tab = table) == null ||
(n = tab.length) == 0)
n = (tab = resize()).length;
if ((first = tab[i = (n - 1) & hash]) != null) {
if (first instanceof TreeNode)
old = (t = (TreeNode<K,V>)first).getTreeNode(hash, key);
else {
Node<K,V> e = first; K k;
do {
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k)))) {
old = e;
break;
}
++binCount;
} while ((e = e.next) != null);
}
}
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;
}
forEach( BiConsumer<? super K, ? super V> action)
/**
* 待补充
*/
@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 (int i = 0; i < tab.length; ++i) {
for (Node<K,V> e = tab[i]; e != null; e = e.next)
action.accept(e.key, e.value);
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
replaceAll( BiFunction<? super K, ? super V, ? extends V> function)
/**
* 待补充
*/
@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 (int i = 0; i < tab.length; ++i) {
for (Node<K,V> e = tab[i]; e != null; e = e.next) {
e.value = function.apply(e.key, e.value);
}
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
Cloning and serialization
clone()
/**
* 浅拷贝。
* clone方法虽然生成了新的HashMap对象，新的HashMap中的table数组虽然也是新生成的，但是数组中的元素还是引用以前的HashMap中的元素。
* 这就导致在对HashMap中的元素进行修改的时候，即对数组中元素进行修改，会导致原对象和clone对象都发生改变，但进行新增或删除就不会影响对方，因为这相当于是对数组做出的改变，clone对象新生成了一个数组。
*
* @return hashMap的浅拷贝
*/
@SuppressWarnings("unchecked")
@Override
public Object clone() {
HashMap<K,V> result;
try {
result = (HashMap<K,V>)super.clone();
} catch (CloneNotSupportedException e) {
throw new InternalError(e);
}
result.reinitialize();
result.putMapEntries(this, false);
return result;
}
loadFactor()
final float loadFactor() { return loadFactor; }
capacity()
final int capacity() {
return (table != null) ? table.length :
(threshold > 0) ? threshold :
DEFAULT_INITIAL_CAPACITY;
}
writeObject( java.io.ObjectOutputStream s)
/**
* 序列化hashMap到ObjectOutputStream中
* 将hashMap的总容量capacity、实际容量size、键值对映射写入到ObjectOutputStream中。键值对映射序列化时是无序的。
*/
private void writeObject(java.io.ObjectOutputStream s)
throws IOException {
int buckets = capacity();
s.defaultWriteObject();
s.writeInt(buckets);
s.writeInt(size);
internalWriteEntries(s);
}
void internalWriteEntries(java.io.ObjectOutputStream s) throws IOException {
Node<K,V>[] tab;
if (size > 0 && (tab = table) != null) {
for (int i = 0; i < tab.length; ++i) {
for (Node<K,V> e = tab[i]; e != null; e = e.next) {
s.writeObject(e.key);
s.writeObject(e.value);
}
}
}
}
/**
* 到ObjectOutputStream中读取hashMap
* 将hashMap的总容量capacity、实际容量size、键值对映射读取出来
*/
private void readObject(java.io.ObjectInputStream s) throws IOException, ClassNotFoundException {
s.defaultReadObject();
reinitialize();
if (loadFactor <= 0 || Float.isNaN(loadFactor))
throw new InvalidObjectException("Illegal load factor: " + loadFactor);
s.readInt();
int mappings = s.readInt();
if (mappings < 0)
throw new InvalidObjectException("Illegal mappings count: " + mappings);
else if (mappings > 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<K,V>[] tab = (Node<K,V>[])new Node[cap];
table = tab;
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
HashIterator
/**
* 待补充
*/
abstract class HashIterator {
Node<K,V> next;
Node<K,V> current;
int expectedModCount;
int index;
HashIterator() {
expectedModCount = modCount;
Node<K,V>[] t = table;
current = next = null;
index = 0;
if (t != null && size > 0) {
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;
K key = p.key;
removeNode(hash(key), key, null, false, false);
expectedModCount = modCount;
}
}
KeyIterator
/**
* key迭代器
*/
final class KeyIterator extends HashIterator
implements Iterator<K> {
public final K next() { return nextNode().key; }
}
ValueIterator
/**
* value迭代器
*/
final class ValueIterator extends HashIterator
implements Iterator<V> {
public final V next() { return nextNode().value; }
}
EntryIterator
/**
* 键值对迭代器
*/
final class EntryIterator extends HashIterator
implements Iterator<Map.Entry<K,V>> {
public final Map.Entry<K,V> next() { return nextNode(); }
}
可分割迭代器
HashMapSpliterator
/**
* 待补充
*/
static class HashMapSpliterator<K,V> {
final HashMap<K,V> map;
Node<K,V> current;
int index;
int fence;
int est;
int expectedModCount;
HashMapSpliterator(HashMap<K,V> m, int origin,
int fence, int est,
int expectedModCount) {
this.map = m;
this.index = origin;
this.fence = fence;
this.est = est;
this.expectedModCount = expectedModCount;
}
final int getFence() {
int hi;
if ((hi = fence) < 0) {
HashMap<K,V> m = map;
est = m.size;
expectedModCount = m.modCount;
Node<K,V>[] tab = m.table;
hi = fence = (tab == null) ? 0 : tab.length;
}
return hi;
}
public final long estimateSize() {
getFence();
return (long) est;
}
}
KeySpliterator
/**
* 待补充
*/
static final class KeySpliterator<K,V>
extends HashMapSpliterator<K,V>
implements Spliterator<K> {
KeySpliterator(HashMap<K,V> m, int origin, int fence, int est,
int expectedModCount) {
super(m, origin, fence, est, expectedModCount);
}
public KeySpliterator<K,V> trySplit() {
int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
return (lo >= mid || current != null) ? null :
new KeySpliterator<>(map, lo, index = mid, est >>>= 1,
expectedModCount);
}
public void forEachRemaining(Consumer<? super K> action) {
int i, hi, mc;
if (action == null)
throw new NullPointerException();
HashMap<K,V> m = map;
Node<K,V>[] tab = m.table;
if ((hi = fence) < 0) {
mc = expectedModCount = m.modCount;
hi = fence = (tab == null) ? 0 : tab.length;
}
else
mc = expectedModCount;
if (tab != null && tab.length >= hi &&
(i = index) >= 0 && (i < (index = hi) || current != null)) {
Node<K,V> p = current;
current = null;
do {
if (p == null)
p = tab[i++];
else {
action.accept(p.key);
p = p.next;
}
} while (p != null || i < hi);
if (m.modCount != mc)
throw new ConcurrentModificationException();
}
}
public boolean tryAdvance(Consumer<? super K> action) {
int hi;
if (action == null)
throw new NullPointerException();
Node<K,V>[] tab = map.table;
if (tab != null && tab.length >= (hi = getFence()) && index >= 0) {
while (current != null || index < hi) {
if (current == null)
current = tab[index++];
else {
K k = current.key;
current = current.next;
action.accept(k);
if (map.modCount != expectedModCount)
throw new ConcurrentModificationException();
return true;
}
}
}
return false;
}
public int characteristics() {
return (fence < 0 || est == map.size ? Spliterator.SIZED : 0) |
Spliterator.DISTINCT;
}
}
ValueSpliterator
/**
* 待补充
*/
static final class ValueSpliterator<K,V>
extends HashMapSpliterator<K,V>
implements Spliterator<V> {
ValueSpliterator(HashMap<K,V> m, int origin, int fence, int est,
int expectedModCount) {
super(m, origin, fence, est, expectedModCount);
}
public ValueSpliterator<K,V> trySplit() {
int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
return (lo >= mid || current != null) ? null :
new ValueSpliterator<>(map, lo, index = mid, est >>>= 1,
expectedModCount);
}
public void forEachRemaining(Consumer<? super V> action) {
int i, hi, mc;
if (action == null)
throw new NullPointerException();
HashMap<K,V> m = map;
Node<K,V>[] tab = m.table;
if ((hi = fence) < 0) {
mc = expectedModCount = m.modCount;
hi = fence = (tab == null) ? 0 : tab.length;
}
else
mc = expectedModCount;
if (tab != null && tab.length >= hi &&
(i = index) >= 0 && (i < (index = hi) || current != null)) {
Node<K,V> p = current;
current = null;
do {
if (p == null)
p = tab[i++];
else {
action.accept(p.value);
p = p.next;
}
} while (p != null || i < hi);
if (m.modCount != mc)
throw new ConcurrentModificationException();
}
}
public boolean tryAdvance(Consumer<? super V> action) {
int hi;
if (action == null)
throw new NullPointerException();
Node<K,V>[] tab = map.table;
if (tab != null && tab.length >= (hi = getFence()) && index >= 0) {
while (current != null || index < hi) {
if (current == null)
current = tab[index++];
else {
V v = current.value;
current = current.next;
action.accept(v);
if (map.modCount != expectedModCount)
throw new ConcurrentModificationException();
return true;
}
}
}
return false;
}
public int characteristics() {
return (fence < 0 || est == map.size ? Spliterator.SIZED : 0);
}
}
EntrySpliterator
/**
* 待补充
*/
static final class EntrySpliterator<K,V>
extends HashMapSpliterator<K,V>
implements Spliterator<Map.Entry<K,V>> {
EntrySpliterator(HashMap<K,V> m, int origin, int fence, int est,
int expectedModCount) {
super(m, origin, fence, est, expectedModCount);
}
public EntrySpliterator<K,V> trySplit() {
int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
return (lo >= mid || current != null) ? null :
new EntrySpliterator<>(map, lo, index = mid, est >>>= 1,
expectedModCount);
}
public void forEachRemaining(Consumer<? super Map.Entry<K,V>> action) {
int i, hi, mc;
if (action == null)
throw new NullPointerException();
HashMap<K,V> m = map;
Node<K,V>[] tab = m.table;
if ((hi = fence) < 0) {
mc = expectedModCount = m.modCount;
hi = fence = (tab == null) ? 0 : tab.length;
}
else
mc = expectedModCount;
if (tab != null && tab.length >= hi &&
(i = index) >= 0 && (i < (index = hi) || current != null)) {
Node<K,V> p = current;
current = null;
do {
if (p == null)
p = tab[i++];
else {
action.accept(p);
p = p.next;
}
} while (p != null || i < hi);
if (m.modCount != mc)
throw new ConcurrentModificationException();
}
}
public boolean tryAdvance(Consumer<? super Map.Entry<K,V>> action) {
int hi;
if (action == null)
throw new NullPointerException();
Node<K,V>[] tab = map.table;
if (tab != null && tab.length >= (hi = getFence()) && index >= 0) {
while (current != null || index < hi) {
if (current == null)
current = tab[index++];
else {
Node<K,V> e = current;
current = current.next;
action.accept(e);
if (map.modCount != expectedModCount)
throw new ConcurrentModificationException();
return true;
}
}
}
return false;
}
public int characteristics() {
return (fence < 0 || est == map.size ? Spliterator.SIZED : 0) |
Spliterator.DISTINCT;
}
}
LinkedHashMap support
下面的几个protected的方法是为了被LinkedHashMap重写设计的，不是为其他子类设计的。几乎所有其他的内部方法也是protected的，但被声明为final，所以可以被LinkedHashMap, view classes和HashSet使用。
newNode( int hash, K key, V value, Node<K,V> next)
/**
* 创建一个常规的（不是树的）node
*/
Node<K,V> newNode(int hash, K key, V value, Node<K,V> next) {
return new Node<>(hash, key, value, next);
}
replacementNode( Node<K,V> p, Node<K,V> next)
/**
* 为了将一个TreeNodes转化为常规的node而设计
* untreeify(HashMap<K,V> map)在使用这个方法
*/
Node<K,V> replacementNode(Node<K,V> p, Node<K,V> next) {
return new Node<>(p.hash, p.key, p.value, next);
}
newTreeNode( int hash, K key, V value, Node<K,V> next)
TreeNode<K,V> newTreeNode(int hash, K key, V value, Node<K,V> next) {
return new TreeNode<>(hash, key, value, next);
}
replacementTreeNode( Node<K,V> p, Node<K,V> next)
TreeNode<K,V> replacementTreeNode(Node<K,V> p, Node<K,V> next) {
return new TreeNode<>(p.hash, p.key, p.value, next);
}
reinitialize()
/**
* 将hashMap重置到初始化的默认状态
* 被clone方法和readObject方法使用。
*/
void reinitialize() {
table = null;
entrySet = null;
keySet = null;
values = null;
modCount = 0;
threshold = 0;
size = 0;
}
afterNodeAccess( Node<K,V> p)
void afterNodeAccess(Node<K,V> p) { }
afterNodeInsertion( boolean evict)
void afterNodeInsertion(boolean evict) { }
afterNodeRemoval( Node
void afterNodeRemoval(Node<K,V> p) { }
internalWriteEntries( java.io.ObjectOutputStream s)
void internalWriteEntries(java.io.ObjectOutputStream s) throws IOException {
Node<K,V>[] tab;
if (size > 0 && (tab = table) != null) {
for (int i = 0; i < tab.length; ++i) {
for (Node<K,V> e = tab[i]; e != null; e = e.next) {
s.writeObject(e.key);
s.writeObject(e.value);
}
}
}
}
TreeNode
定义
/**
* 树节点。
* 继承LinkedHashMap.Entry，所以可以被用作常规node或者链node的扩展
*/
static final class TreeNode<K,V> extends LinkedHashMap.Entry<K,V> {}
域
TreeNode<K,V> parent;
TreeNode<K,V> left;
TreeNode<K,V> right;
TreeNode<K,V> prev;
boolean red;
构造函数
TreeNode(int hash, K key, V val, Node<K,V> next) {
super(hash, key, val, next);
}
方法
待补充
HashMap就先讲到这里，关于Java8和Java7的HashMap实现方式的不同，扩容机制详解、TreeNode详解以后会补充。
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作者：panweiwei1994 发表于2017/8/19 20:38:27
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