java集合之HashMap源码学习

　　 |-- Node<K,V>[] table; // 存数据的结构
        int threshold;
        
    |-- new HashMap<>() {
            // DEFAULT_LOAD_FACTOR = 0.75f
            this.loadFactor = DEFAULT_LOAD_FACTOR; // all other fields defaulted
        }
    |-- put(key, value) {
            Node<K,V>[] tab;
            int n;
            int i; // i = (tab.length - 1) & hash
            boolean isTableEmpty = (tab = table) == null || (n = tab.length) == 0;
            if (isTableEmpty) 
                n = (tab = resize()).length;
            boolean isValueEmpty = ((p = tab[i = (n - 1) & hash]) == null);
            if (isValueEmpty) 
                tab[i] = newNode(hash, key, value, null);
            else {
                // TODO 
                Node<K,V> e;
                boolean isEqHashAndKey = p.hash == hash && ((k = p.key) == key || (key != null && key.equals(k));
                if (isEqHashAndKey)
                    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) // -1 for 1st
                                treeifyBin(tab, hash);
                            break;
                        }
                        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();
        }
    |-- 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) { // >= 2的30次方
                    threshold = Integer.MAX_VALUE; // = (2的31次方-1)
                    return oldTab;
                } else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&
                    oldCap >= DEFAULT_INITIAL_CAPACITY){ // (oldCap x 2) < 2的30次方 && oldCap >= 16
                    newThr = oldThr << 1; // double threshold
                }
            }
            else if (oldThr > 0) // initial capacity was placed in threshold
                newCap = oldThr;
            else {               // zero initial threshold signifies using defaults
                newCap = DEFAULT_INITIAL_CAPACITY;    // 16
                newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY); // 0.75*16
            }
            if (newThr == 0) {
                float ft = (float)newCap * loadFactor;
                newThr = (newCap < MAXIMUM_CAPACITY && ft < (float)MAXIMUM_CAPACITY ?
                          (int)ft : Integer.MAX_VALUE); // 
            }
            threshold = newThr;
            Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];
            table = newTab;
            if (oldTab != null) {
                // TODO 
            }
            return newTab;
        }
    |-- get(key) {
            Node<K,V>[] tab; Node<K,V> first, e; int n; K k;
            boolean isExsitsFirst = ((tab = table) != nul && (n = tab.length) > 0 &&
                (first = tab[(n - 1) & hash]) != null);
            if (isExsitsFirst) {
                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);
                }
            }
        }