202109040709 - HashMap源码

putVal()方法

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)  
            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();  
 afterNodeInsertion(evict);  
 return null;}