1.類聲明:
public class HashMap<K,V> extends AbstractMap<K,V>
implements Map<K,V>, Cloneable, Serializable {}
2.變量:
//默認初始化容量
static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; // aka 16
//最大容量
static final int MAXIMUM_CAPACITY = 1 << 30;
//默認加載因子
static final float DEFAULT_LOAD_FACTOR = 0.75f;
//對於table裏面的每個列表,從鏈表結構轉爲紅黑樹結構的閾值
static final int TREEIFY_THRESHOLD = 8;
//對於table裏面的每個列表,從紅黑樹結構轉爲列表結構的閾值
static final int UNTREEIFY_THRESHOLD = 6;
//最小樹化容量。只有當表的容量達到這個閾值,才能從列表結構轉爲樹結構
static final int MIN_TREEIFY_CAPACITY = 64;
//當改變了表的映射數目(put方法增加了新的Node節點)或者修改了表結構(remove(),clear())的時候,進行+1,若是對map進行迭代的時候,發生modCount不是期望的modCount,即被修改了,則拋出ConcurrentModificationException異常
transient int modCount;
3.方法:
//找到不小於cap的最小的2的n次方,這個算法之精闢令人歎爲觀止。
具體可見參考文章1。通過右移使得cap-1表示的二進制數每一位都變成1。最後加1得到所需數。
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;
}
//put方法
public V put(K key, V value) {
return putVal(hash(key), key, value, false, true);
}
//若onlyIfAbsent爲true,不會覆蓋掉舊值,若爲false,會覆蓋掉舊值
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)//如果是TreeNode節點
e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
else {//如果是鏈表節點
for (int binCount = 0; ; ++binCount) {
if ((e = p.next) == null) {
p.next = newNode(hash, key, value, null);//往鏈表尾部插入節點,jdk7是往鏈表頭部插入節點。
//當鏈表數量大於樹化閾值時,進行樹化操作,對應的當remove的時候會有一個鏈表化的操作
if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
treeifyBin(tab, hash);
break;
}
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
break;
p = e;
}
}
//如果找到了舊的數據,則根據onlyIfAbsent值決定是否更新
if (e != null) { // existing mapping for key
V oldValue = e.value;
if (!onlyIfAbsent || oldValue == null)
e.value = value;
afterNodeAccess(e);
return oldValue;
}
}
++modCount;//當增加了新的node時,修改次數+1
if (++size > threshold)
resize();
afterNodeInsertion(evict);
return null;
}
//往樹結構中插入數據
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;
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;
}
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;
moveRootToFront(tab, balanceInsertion(root, x));
return null;
}
}
}
參考文章:1.http://blog.csdn.net/fan2012huan/article/details/51097331
2.http://blog.csdn.net/crazy1235/article/details/75579654