1.jdk1.8的結構
數組 + 鏈表 + 紅黑樹
2.鏈表
Node
hash
key
value
nextNode
3.數組
Node[] table
4.數組的長度是2的n次方
1.任何數和2的n次方-1做與運算都小於等於在2的n次方-1
剛好用來做hash計算數組的位子
2.任何數和2的n次方做與運算,只有兩種結果0或者2的n次方
這個可以在resize的時候確定節點是高位和地位
5.put操作
如果hash出來的數組沒有值,新建一個Node
if ((p = tab[i = (n - 1) & hash]) == null)
tab[i] = newNode(hash, key, value, null);
public V put(K key, V value) {
return putVal(hash(key), key, value, false, true);
}
/**
* 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
*/
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)
//如果數組爲空,先初始化
n = (tab = resize()).length;
if ((p = tab[i = (n - 1) & hash]) == null)
//如果hash出來的數組沒有值,新建一個Node
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))))
//如果hash、key相等 值相等就替換
e = p;
else if (p instanceof TreeNode)
//如果是p是個樹
e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
else {
for (int binCount = 0; ; ++binCount) {
//死循環訪問鏈表,直到最後一個節點(p.next)
if ((e = p.next) == null) {
p.next = newNode(hash, key, value, null);
if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
//如果鏈表的長度大於 8-1,需要轉成紅黑樹
treeifyBin(tab, hash);
break;
}
//如果鏈表中存在和key相等的元素跳出循環
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
break;
p = e;
}
}
if (e != null) { // existing mapping for key
//有key相等的
V oldValue = e.value;
if (!onlyIfAbsent || oldValue == null)
e.value = value;
afterNodeAccess(e);
return oldValue;
}
}
++modCount;
if (++size > threshold)
resize();
afterNodeInsertion(evict);
return null;
}