hashmap(1.8)

1、hashmap父接口AbstractMap，實現Map、CloneAble、Seralizeable接口

2、初始容量：2<<3；負載因子：0.75（默認）

3、hashmap結構由：數組、列表、紅黑樹（1.8新增）組成

hashmap.put(Object o,Object o)

public V put(K key, V value) {return putVal(hash(key), key, value, false, true);}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)//判斷table是否為空，空的話新建（resize）n = (tab = resize()).length;if ((p = tab[i = (n - 1) & hash]) == null)//對null進行處理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key存在則直接覆蓋e = p;else if (p instanceof TreeNode)//判斷是否為樹結構，是的話按照樹進行插入e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);else {//單向鏈表，循環進行處理for (int binCount = 0; ; ++binCount) {if ((e = p.next) == null) {//如果桶為沒有，則直接賦值p.next = newNode(hash, key, value, null);if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st 判斷長度是否超過8，超過的話則將單向鏈表轉為紅黑樹treeifyBin(tab, hash);break;}if (e.hash == hash &&((k = e.key) == key || (key != null && key.equals(k))))//存在該key，則直接覆蓋break;p = e;}}if (e != null) { // existing mapping for keyV oldValue = e.value;if (!onlyIfAbsent || oldValue == null)e.value = value;afterNodeAccess(e);return oldValue;}}++modCount;if (++size > threshold)//判斷是否擴容，兩倍resize();afterNodeInsertion(evict);return null;}

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hashmap.get

public V get(Object key) {Node<K,V> e;return (e = getNode(hash(key), key)) == null ? null : e.value;}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 && // always check first node((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;}

擴容resize()

final Node<K,V>[] resize() {Node<K,V>[] oldTab = table;int oldCap = (oldTab == null) ? 0 : oldTab.length;//舊表容量int oldThr = threshold;//容量*負載因子（capacity * load factor）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)//兩倍擴容，且小于最大capacity（1<<30）newThr = oldThr << 1; // double threshold}else if (oldThr > 0) // initial capacity was placed in thresholdnewCap = oldThr;else { // zero initial threshold signifies using defaultsnewCap = 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) {//判斷是否有無就table，沒有則直接返回，有則擴容（hashmap.put）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 { // preserve orderNode<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;elseloTail.next = e;loTail = e;}else {if (hiTail == null)hiHead = e;elsehiTail.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;}

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posted @ 2018-05-22 12:22 犇犇丶 閱讀(...) 評論(...) 編輯 收藏

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