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public class HashMapTest { public static void main(String[] args) { HashMapThread thread0 = new HashMapThread(); HashMapThread thread1 = new HashMapThread(); HashMapThread thread2 = new HashMapThread(); HashMapThread thread3 = new HashMapThread(); HashMapThread thread4 = new HashMapThread(); thread0.start(); thread1.start(); thread2.start(); thread3.start(); thread4.start(); }}class HashMapThread extends Thread { private static AtomicInteger ai = new AtomicInteger(); private static Map map = new HashMap<>(); @Override public void run() { while (ai.get() < ) { map.put(ai.get(),源码资本结构 ai.get()); ai.incrementAndGet(); } }}
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final V putVal(int hash, K key, V value, boolean onlyIfAbsent, boolean evict) { Node[] tab; Node p; int n, i; if ((tab = table) == null || (n = tab.length) == 0) n = (tab = resize()).length; if ((p = tab[i = (n - 1) & hash]) == null) // å¦æ没æhash碰æåç´æ¥æå ¥å ç´ tab[i] = newNode(hash, key, value, null); else { Node 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)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; } è¿æ¯jdk1.8ä¸HashMapä¸putæä½ç主å½æ°ï¼ 注æ第6è¡ä»£ç ï¼å¦æ没æhash碰æåä¼ç´æ¥æå ¥å ç´ ãå¦æ线ç¨Aå线ç¨Båæ¶è¿è¡putæä½ï¼å好è¿ä¸¤æ¡ä¸åçæ°æ®hashå¼ä¸æ ·ï¼å¹¶ä¸è¯¥ä½ç½®æ°æ®ä¸ºnullï¼æ以è¿çº¿ç¨AãBé½ä¼è¿å ¥ç¬¬6è¡ä»£ç ä¸ã
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