//构造方法
public HashMap() {
this.loadFactor = DEFAULT_LOAD_FACTOR; // 加载因子
}
public HashMap(int initialCapacity) {
this(initialCapacity, DEFAULT_LOAD_FACTOR);
}
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);
}
//直接传递一个map作为构造参数。
public HashMap(Map<? extends K, ? extends V> m) {
this.loadFactor = DEFAULT_LOAD_FACTOR;
putMapEntries(m, false);//调用 01
}
//01
final void putMapEntries(Map<? extends K, ? extends V> m, boolean evict) {
int s = m.size();
if (s > 0) {
if (table == null) { // pre-size
float ft = ((float)s / loadFactor) + 1.0F;//需要扩展的次数
int t = ((ft < (float)MAXIMUM_CAPACITY) ?
(int)ft : MAXIMUM_CAPACITY);//判断是否大于最大值
if (t > threshold)
threshold = tableSizeFor(t);//得到最近的2的整数次幂的数
}
else if (s > threshold)
resize();//重新计算大小 跳转 02
for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) {//遍历
K key = e.getKey();
V value = e.getValue();
//首先计算hash，然后存储到新对象 跳转 03，然后04
putVal(hash(key), key, value, false, evict);
}
}
}
//02
//初始化或者扩容之后元素调整
final Node<K,V>[] resize() {
// 获取旧元素数组的各种信息
Node<K,V>[] oldTab = table;
// 长度
int oldCap = (oldTab == null) ? 0 : oldTab.length;
// 扩容的临界值
int oldThr = threshold;
// 定义新数组的长度及扩容的临界值
int newCap, newThr = 0;
if (oldCap > 0) { // 如果原table不为空
// 如果数组长度达到最大值，则修改临界值为Integer.MAX_VALUE
if (oldCap >= MAXIMUM_CAPACITY) {
threshold = Integer.MAX_VALUE;
return oldTab;
}
// 下面就是扩容操作（2倍）
else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&
oldCap >= DEFAULT_INITIAL_CAPACITY)
// threshold也变为二倍
newThr = oldThr << 1;
}
else if (oldThr > 0) // initial capacity was placed in threshold
newCap = oldThr;
else { // threshold为0，则使用默认值
newCap = DEFAULT_INITIAL_CAPACITY;
newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);
}
if (newThr == 0) { // 如果临界值还为0，则设置临界值
float ft = (float)newCap * loadFactor;
newThr = (newCap < MAXIMUM_CAPACITY && ft < (float)MAXIMUM_CAPACITY ?
(int)ft : Integer.MAX_VALUE);
}
threshold = newThr; // 更新填充因子
@SuppressWarnings({"rawtypes","unchecked"})
Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];
table = newTab;
if (oldTab != null) { // 调整数组大小之后，需要调整红黑树或者链表的指向
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) // 红黑树调整
((TreeNode<K,V>)e).split(this, newTab, j, oldCap);
else { // preserve order
// 链表调整
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;
}
//03
static final int hash(Object key) {
int h;
return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
}
存值：哈希表hashtable(key，value) 就是把Key通过一个固定的算法函数既所谓的哈希函数转换成一个整型数字，然后就将该数字对数组长度进行取余，取余结果就当作数组的下标，将value存储在以该数字为下标的数组空间里。
//04
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
boolean evict) {
Node<K,V>[] tab; Node<K,V> p; int n, i;//tab就算hashmap的数组。 p为数组的一个节点也是一个链表的端点。
if ((tab = table) == null || (n = tab.length) == 0)
n = (tab = resize()).length;//数组为空，重新计算。
if ((p = tab[i = (n - 1) & hash]) == null)//除法散列法进行散列(数组层次为空一定不会碰撞)。取出应该存入的链表的端点。如果链表为空，进入if内
tab[i] = newNode(hash, key, value, null);//创建node对象，并且放入链表端点。
else {
Node<K,V> e; K k;
if (p.hash == hash &&//与端点的hash对比，hashcode相等，然后使用下一个判断
((k = p.key) == key || (key != null && key.equals(k))))//判断是否是同一个对象
e = p;
else if (p instanceof TreeNode)//如果是红黑树结点的话，进行红黑树插入
e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);//跳转 05
else {//不是红黑树，是长度小于8的链表
for (int binCount = 0; ; ++binCount) {//遍历判断在链表中哪一个有碰撞
if ((e = p.next) == null) {//遍历链表，如果是到了链表尾部，则创建新节点
p.next = newNode(hash, key, value, null);//则创建新节点
if (binCount >= TREEIFY_THRESHOLD - 1) // 判断长度是否大于等于8，
treeifyBin(tab, hash);//转换为树 跳转 06
break;
}
//遍历 判断是否是同一个对象
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
break;
p = e;
}
}
if (e != null) { // existing mapping for key
V oldValue = e.value;
if (!onlyIfAbsent || oldValue == null)
e.value = value;
afterNodeAccess(e);
return oldValue;
}
}
++modCount;
if (++size > threshold)
resize();
afterNodeInsertion(evict);
return null;
}//05
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;
TreeNode<K,V> root = (parent != null) ? root() : this;// 判断是否有根节点，没有则设置自己。
for (TreeNode<K,V> p = root;;) {// 遍历树
int dir, ph; K pk;
if ((ph = p.hash) > h)// 判断hash值大小，决定放在左子树还是右子树
dir = -1;
else if (ph < h)
dir = 1;
else if ((pk = p.key) == k || (k != null && k.equals(pk)))//是同一个
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;
}
dir = tieBreakOrder(k, pk);//用类名转ascii作对比
}
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;
moveRootToFront(tab, balanceInsertion(root, x));//重新平衡树
return null;
}
}
}//06
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);//转换为树节点。
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);//转为真正的平衡树二叉树。跳转07
}
}//07
final void treeify(Node<K,V>[] tab) {
TreeNode<K,V> root = null;
for (TreeNode<K,V> x = this, next; x != null; x = next) {
next = (TreeNode<K,V>)x.next;
x.left = x.right = null;//树的左右孩子置空
if (root == null) {//根
x.parent = null;
x.red = false;//黑色
root = x;
}
else {
K k = x.key;
int h = x.hash;
Class<?> kc = null;
for (TreeNode<K,V> p = root;;) {//遍历树
int dir, ph;
K pk = p.key;
if ((ph = p.hash) > h)//对比hash值，决定左子树还是右子树
dir = -1;
else if (ph < h)
dir = 1;
else if ((kc == null &&
(kc = comparableClassFor(k)) == null) ||
(dir = compareComparables(kc, k, pk)) == 0)
dir = tieBreakOrder(k, pk);//ascii对比、identityHashCode对比
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;
root = balanceInsertion(root, x);//平衡树
break;
}
}
}
}
moveRootToFront(tab, root);
}