{"id":108,"date":"2020-02-10T11:47:39","date_gmt":"2020-02-10T03:47:39","guid":{"rendered":"https:\/\/www.zeroheart.xyz\/wordpress\/?p=108"},"modified":"2020-07-05T11:42:09","modified_gmt":"2020-07-05T03:42:09","slug":"hashmap%e7%ae%80%e5%8d%95%e8%ae%b0%e5%bd%95","status":"publish","type":"post","link":"https:\/\/www.zeroheart.xyz\/wordpress\/?p=108","title":{"rendered":"hashmap\u7b80\u5355\u8bb0\u5f55"},"content":{"rendered":"\n<ul><li>\u5bb9\u91cf\u8bbe\u8ba1<\/li><li>\u6269\u5bb9<\/li><\/ul>\n\n\n\n<h4 class=\"wp-block-heading\">\u5bb9\u91cf\u8bbe\u8ba1<\/h4>\n\n\n\n<p>hashmap \u9ed8\u8ba4\u5927\u5c0f\u662f2^4\uff0c\u6269\u5bb9\u662f\u6210\u500d\u7684<\/p>\n\n\n\n<p>key\u8fdb\u884c\u53d6\u6a21\u4e4b\u540e\uff0c\u4f1a\u653e\u5230\u5bf9\u5e94\u7684index\u3002<\/p>\n\n\n\n<p>\u5bb9\u91cf\u662f2\u7684n\u6b21\u5e42\uff0c\u4e5f\u662f\u5bf9\u53d6\u6a21\u8fd0\u7b97\u7684\u4f18\u5316\u3002\u6bd4\u5982\u5bb9\u91cf\u4e3a8\uff0c\u53d6\u6a21\u516c\u5f0f\u662f h % 8\uff0c8\u76842\u8fdb\u5236\u662f1000\uff0chashmap\u4e2d\u7684\u8ba1\u7b97\uff0c\u4f18\u5316\u4e3a h &amp; (8-1) \u5373 h &amp; 7 = h &amp; 0111<\/p>\n\n\n\n<p>\u5c31\u662f\u8bf4\u53d6h\u4e8c\u8fdb\u5236\u7684\u540e\u4e09\u4f4d\u3002\u4e8c\u8fdb\u5236\u8fd0\u7b97\u901f\u5ea6\u5feb\uff0c\u6b63\u662f\u5bb9\u91cf\u7684\u8003\u8651\u624d\u80fd\u505a\u8fd9\u79cd\u4f18\u5316\u3002<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">\u6269\u5bb9<\/h4>\n\n\n\n<p>\u6269\u5bb9\u65f6\u5019\uff0c\u5bb9\u91cf\u4e3a\u53d8\u4e3a\u4e24\u500d\u3002\u6b64\u65f6\u4f1a\u8fdb\u884c\u4f4d\u7f6e\u7684\u79fb\u52a8\uff0c\u539f\u6765\u7684key\u7684hashcode\uff0c\u5047\u8bbe\u662f100011110\uff0c\u5bb9\u91cf\u662f8 1000<\/p>\n\n\n\n<p>\u90a3\u4e48\u539f\u6765\u7684index \u4e3a 100011110 &amp; 0111 = 110 = 6<br>\n\u6269\u5bb9\u540e\u7684\u4f4d\u7f6e\u600e\u4e48\u786e\u5b9a\uff0c\u53ef\u4ee5\u76f4\u63a5\u770b100011110\u540e\u56db\u4f4d 1110\uff0c\u9ad8\u4f4d\u4e3a1\uff0c\u90a3\u5c31\u662f\u79fb\u52a8\u52306+8\u7684\u4f4d\u7f6e = 14<\/p>\n\n\n\n<p>\u540c\u6837\u7684\uff0c\u5047\u8bbe\u539f\u6765\u7684index \u4e3a 100010110 &amp; 0111 = 110 = 6<br>\n\u6269\u5bb9\u540e\u770b100011110\u540e\u56db\u4f4d 0110\uff0c\u9ad8\u4f4d\u4e3a0\uff0c\u90a3\u5c31\u4fdd\u6301\u5f53\u524d\u7684\u4f4d\u7f6e6\u4e0d\u53d8<\/p>\n\n\n\n<p>\u51cf\u5c11\u4e86\u79fb\u52a8\uff0ce.hash &amp; oldCap \uff0c\u8fd9\u91cc\u662fhash &amp; 8 = h &amp; 1000\u53d6\u6700\u9ad8\u4f4d\u3002if(e.hash &amp; oldCap)==0\uff0c\u653e\u5230\u539f\u59cbindex\uff0cif(e.hash &amp; oldCap)==1\uff0c\u653e\u5230\u539f\u59cbindex+oldCap\u7684\u4f4d\u7f6e\u3002<\/p>\n\n\n\n<p class=\"has-text-color has-luminous-vivid-orange-color\">jdk1.8\u4e2d\u8d85\u8fc7\u4e86hash\u51b2\u7a81\u5bfc\u81f4\u94fe\u8868\u957f\u5ea6>=(8-1)\uff0c\u65f6\u5019\uff0c\u4f1a\u628a\u94fe\u8868\u8f6c\u5316\u6210\u7ea2\u9ed1\u6811\u5b58\u50a8\uff0c\u63d0\u9ad8\u4e86\u67e5\u8be2\u6548\u7387\u3002<\/p>\n\n\n\n<pre class=\"wp-block-preformatted\">hashMap\u7ebf\u7a0b\u4e0d\u5b89\u5168\u7684\u539f\u56e0\uff1a<br><a href=\"https:\/\/www.zeroheart.xyz\/wordpress\/?p=1057\">https:\/\/www.zeroheart.xyz\/wordpress\/?p=1057<\/a><\/pre>\n\n\n\n<p>\u540e\u7eed\u6587\u7ae0\u53c2\u8003\uff1a<a href=\"https:\/\/mp.weixin.qq.com\/s\/AixdbEiXf3KfE724kg2YIw\">https:\/\/mp.weixin.qq.com\/s\/AixdbEiXf3KfE724kg2YIw\ufeff<\/a><\/p>\n\n\n\n<p>\u6839\u636e\u6cca\u677e\u5206\u5e03\uff0c\u5728\u8d1f\u8f7d\u56e0\u5b50\u9ed8\u8ba4\u4e3a0.75\u7684\u65f6\u5019\uff0c\u5355\u4e2ahash\u69fd\u5185\u5143\u7d20\u4e2a\u6570\u4e3a8\u7684\u6982\u7387\u5c0f\u4e8e\u767e\u4e07\u5206\u4e4b\u4e00\uff0c\u6240\u4ee5\u5c067\u4f5c\u4e3a\u4e00\u4e2a\u5206\u6c34\u5cad\uff0c\u7b49\u4e8e7\u7684\u65f6\u5019\u4e0d\u8f6c\u6362\uff0c\u5927\u4e8e\u7b49\u4e8e8\u7684\u65f6\u5019\u624d\u8fdb\u884c\u8f6c\u6362\uff0c\u5c0f\u4e8e\u7b49\u4e8e6\u7684\u65f6\u5019\u5c31\u5316\u4e3a\u94fe\u8868\u3002<\/p>\n\n\n\n<pre class=\"wp-block-preformatted\">hashTable \u662f\u5b89\u5168\u7684\uff0c\u4f46\u662f\u90fd\u662f\u7528synchronized\u52a0\u9501\u7684\uff0c\u6240\u4ee5\u6548\u7387\u5e95\u4e0b\uff0cHashtable \u662f\u4e0d\u5141\u8bb8\u952e\u6216\u503c\u4e3a null \u7684\uff0cHashMap \u7684\u952e\u503c\u5219\u90fd\u53ef\u4ee5\u4e3a null\u3002\u8fd9\u662f\u56e0\u4e3aHashtable\u4f7f\u7528\u7684\u662f<strong>\u5b89\u5168\u5931\u8d25\u673a\u5236\uff08fail-safe\uff09<\/strong>\uff0c\u8fd9\u79cd\u673a\u5236\u4f1a\u4f7f\u4f60\u6b64\u6b21\u8bfb\u5230\u7684\u6570\u636e\u4e0d\u4e00\u5b9a\u662f\u6700\u65b0\u7684\u6570\u636e\u3002<br><br>\u5982\u679c\u4f60\u4f7f\u7528null\u503c\uff0c\u5c31\u4f1a\u4f7f\u5f97\u5176\u65e0\u6cd5\u5224\u65ad\u5bf9\u5e94\u7684key\u662f\u4e0d\u5b58\u5728\u8fd8\u662f\u4e3a\u7a7a\uff0c\u56e0\u4e3a\u4f60\u65e0\u6cd5\u518d\u8c03\u7528\u4e00\u6b21contain(key\uff09\u6765\u5bf9key\u662f\u5426\u5b58\u5728\u8fdb\u884c\u5224\u65ad\uff0cConcurrentHashMap\u540c\u7406\u3002<br><br><strong>\u5b9e\u73b0\u65b9\u5f0f\u4e0d\u540c<\/strong>\uff1aHashtable \u7ee7\u627f\u4e86 Dictionary\u7c7b\uff0c\u800c HashMap \u7ee7\u627f\u7684\u662f AbstractMap \u7c7b\u3002<br>Dictionary \u662f JDK 1.0 \u6dfb\u52a0\u7684\uff0c\u6ca1\u7528\u8fc7\u3002<br><strong>\u521d\u59cb\u5316\u5bb9\u91cf\u4e0d\u540c<\/strong>\uff1aHashMap \u7684\u521d\u59cb\u5bb9\u91cf\u4e3a\uff1a16\uff0cHashtable \u521d\u59cb\u5bb9\u91cf\u4e3a\uff1a11\uff0c\u4e24\u8005\u7684\u8d1f\u8f7d\u56e0\u5b50\u9ed8\u8ba4\u90fd\u662f\uff1a0.75\u3002<br><strong>\u6269\u5bb9\u673a\u5236\u4e0d\u540c<\/strong>\uff1a\u5f53\u73b0\u6709\u5bb9\u91cf\u5927\u4e8e\u603b\u5bb9\u91cf * \u8d1f\u8f7d\u56e0\u5b50\u65f6\uff0cHashMap \u6269\u5bb9\u89c4\u5219\u4e3a\u5f53\u524d\u5bb9\u91cf\u7ffb\u500d\uff0cHashtable \u6269\u5bb9\u89c4\u5219\u4e3a\u5f53\u524d\u5bb9\u91cf\u7ffb\u500d + 1\u3002<br><strong>\u8fed\u4ee3\u5668\u4e0d\u540c<\/strong>\uff1aHashMap \u4e2d\u7684 Iterator \u8fed\u4ee3\u5668\u662f fail-fast \u7684\uff0c\u800c Hashtable \u7684 Enumerator \u4e0d\u662f fail-fast \u7684\u3002<br>\u6240\u4ee5\uff0c\u5f53\u5176\u4ed6\u7ebf\u7a0b\u6539\u53d8\u4e86HashMap \u7684\u7ed3\u6784\uff0c\u5982\uff1a\u589e\u52a0\u3001\u5220\u9664\u5143\u7d20\uff0c\u5c06\u4f1a\u629b\u51faConcurrentModificationException \u5f02\u5e38\uff0c\u800c Hashtable \u5219\u4e0d\u4f1a\u3002<\/pre>\n\n\n\n<p>cuncurrentHashMap<\/p>\n\n\n\n<p>1.7\u91cc\u9762\u8fd8\u662f\u6570\u7ec4\u52a0\u94fe\u8868\uff0c\u589e\u52a0\u4e86segment\u7684\u6982\u5ff5<\/p>\n\n\n\n<figure class=\"wp-block-image\"><img loading=\"lazy\" decoding=\"async\" width=\"768\" height=\"657\" src=\"https:\/\/www.zeroheart.xyz\/wordpress\/wp-content\/uploads\/2020\/06\/image-15.png\" alt=\"\" class=\"wp-image-853\" srcset=\"https:\/\/www.zeroheart.xyz\/wordpress\/wp-content\/uploads\/2020\/06\/image-15.png 768w, https:\/\/www.zeroheart.xyz\/wordpress\/wp-content\/uploads\/2020\/06\/image-15-300x257.png 300w\" sizes=\"(max-width: 768px) 100vw, 768px\" \/><\/figure>\n\n\n\n<p>Segment \u662f ConcurrentHashMap \u7684\u4e00\u4e2a\u5185\u90e8\u7c7b\uff0c\u4e3b\u8981\u7684\u7ec4\u6210\u5982\u4e0b\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>static final class Segment&lt;K,V> extends ReentrantLock implements Serializable {\n\n    private static final long serialVersionUID = 2249069246763182397L;\n\n    \/\/ \u548c HashMap \u4e2d\u7684 HashEntry \u4f5c\u7528\u4e00\u6837\uff0c\u771f\u6b63\u5b58\u653e\u6570\u636e\u7684\u6876\n    transient volatile HashEntry&lt;K,V>[] table;\n\n    transient int count;\n        \/\/ \u8bb0\u5f97\u5feb\u901f\u5931\u8d25\uff08fail\u2014fast\uff09\u4e48\uff1f\n    transient int modCount;\n        \/\/ \u5927\u5c0f\n    transient int threshold;\n        \/\/ \u8d1f\u8f7d\u56e0\u5b50\n    final float loadFactor;\n\n}<\/code><\/pre>\n\n\n\n<p>HashEntry\u8ddfHashMap\u5dee\u4e0d\u591a\u7684\uff0c\u4f46\u662f\u4e0d\u540c\u70b9\u662f\uff0c\u4ed6\u4f7f\u7528volatile\u53bb\u4fee\u9970\u4e86\u4ed6\u7684\u6570\u636eValue\uff0c\u8fd8\u6709\u4e0b\u4e00\u4e2a\u8282\u70b9next\u3002<\/p>\n\n\n\n<pre class=\"wp-block-preformatted\">\u539f\u7406\u4e0a\u6765\u8bf4\uff0cConcurrentHashMap \u91c7\u7528\u4e86<strong>\u5206\u6bb5\u9501<\/strong>\u6280\u672f\uff0c\u5176\u4e2d Segment \u7ee7\u627f\u4e8e ReentrantLock\u3002<br>\u4e0d\u4f1a\u50cf HashTable \u90a3\u6837\u4e0d\u7ba1\u662f put \u8fd8\u662f get \u64cd\u4f5c\u90fd\u9700\u8981\u505a\u540c\u6b65\u5904\u7406\uff0c\u7406\u8bba\u4e0a ConcurrentHashMap \u652f\u6301 CurrencyLevel (Segment \u6570\u7ec4\u6570\u91cf)\u7684\u7ebf\u7a0b\u5e76\u53d1\u3002<br>\u6bcf\u5f53\u4e00\u4e2a\u7ebf\u7a0b\u5360\u7528\u9501\u8bbf\u95ee\u4e00\u4e2a Segment \u65f6\uff0c\u4e0d\u4f1a\u5f71\u54cd\u5230\u5176\u4ed6\u7684 Segment\u3002<br>\u5c31\u662f\u8bf4\u5982\u679c\u5bb9\u91cf\u5927\u5c0f\u662f16\u4ed6\u7684\u5e76\u53d1\u5ea6\u5c31\u662f16\uff0c\u53ef\u4ee5\u540c\u65f6\u5141\u8bb816\u4e2a\u7ebf\u7a0b\u64cd\u4f5c16\u4e2aSegment\u800c\u4e14\u8fd8\u662f\u7ebf\u7a0b\u5b89\u5168\u7684\u3002<br><br><br>get \u903b\u8f91\u6bd4\u8f83\u7b80\u5355\uff0c\u53ea\u9700\u8981\u5c06 Key \u901a\u8fc7 Hash \u4e4b\u540e\u5b9a\u4f4d\u5230\u5177\u4f53\u7684 Segment \uff0c\u518d\u901a\u8fc7\u4e00\u6b21 Hash \u5b9a\u4f4d\u5230\u5177\u4f53\u7684\u5143\u7d20\u4e0a\u3002<br>\u7531\u4e8e HashEntry \u4e2d\u7684 value \u5c5e\u6027\u662f\u7528 volatile \u5173\u952e\u8bcd\u4fee\u9970\u7684\uff0c\u4fdd\u8bc1\u4e86\u5185\u5b58\u53ef\u89c1\u6027\uff0c\u6240\u4ee5\u6bcf\u6b21\u83b7\u53d6\u65f6\u90fd\u662f\u6700\u65b0\u503c\u3002<br>ConcurrentHashMap \u7684 get \u65b9\u6cd5\u662f\u975e\u5e38\u9ad8\u6548\u7684\uff0c<strong>\u56e0\u4e3a\u6574\u4e2a\u8fc7\u7a0b\u90fd\u4e0d\u9700\u8981\u52a0\u9501<\/strong>\u3002<br><br><\/pre>\n\n\n\n<pre class=\"wp-block-preformatted\">1.8\u91cc\u9762\u629b\u5f03\u4e86\u539f\u6709\u7684 Segment \u5206\u6bb5\u9501\uff0c\u800c\u91c7\u7528\u4e86 <code>CAS + synchronized\uff08\u4f18\u5316\u8fc7\u7684\uff0c\u6709\u9501\u5347\u7ea7\u7684\u6b65\u9aa4\uff09<\/code>&nbsp;\u6765\u4fdd\u8bc1\u5e76\u53d1\u5b89\u5168\u6027\u3002<br><br>\u8ddfHashMap\u5f88\u50cf\uff0c\u4e5f\u628a\u4e4b\u524d\u7684HashEntry\u6539\u6210\u4e86Node\uff0c\u4f46\u662f\u4f5c\u7528\u4e0d\u53d8\uff0c\u628a\u503c\u548cnext\u91c7\u7528\u4e86volatile\u53bb\u4fee\u9970\uff0c\u4fdd\u8bc1\u4e86\u53ef\u89c1\u6027\uff0c\u5e76\u4e14\u4e5f\u5f15\u5165\u4e86\u7ea2\u9ed1\u6811\uff0c\u5728\u94fe\u8868\u5927\u4e8e\u4e00\u5b9a\u503c\u7684\u65f6\u5019\u4f1a\u8f6c\u6362\uff08\u9ed8\u8ba4\u662f8\uff09\u3002<br><br>ConcurrentHashMap\u5728\u8fdb\u884cput\u64cd\u4f5c\u7684\u8fd8\u662f\u6bd4\u8f83\u590d\u6742\u7684\uff0c\u5927\u81f4\u53ef\u4ee5\u5206\u4e3a\u4ee5\u4e0b\u6b65\u9aa4\uff1a<br>1.\u6839\u636e key \u8ba1\u7b97\u51fa hashcode \u3002<br>2.\u5224\u65ad\u662f\u5426\u9700\u8981\u8fdb\u884c\u521d\u59cb\u5316\u3002<br>3.\u5373\u4e3a\u5f53\u524d key \u5b9a\u4f4d\u51fa\u7684 Node\uff0c\u5982\u679c\u4e3a\u7a7a\u8868\u793a\u5f53\u524d\u4f4d\u7f6e\u53ef\u4ee5\u5199\u5165\u6570\u636e\uff0c\u5229\u7528 CAS \u5c1d\u8bd5\u5199\u5165\uff0c\u5931\u8d25\u5219\u81ea\u65cb\u4fdd\u8bc1\u6210\u529f\u3002<br>4.\u5982\u679c\u5f53\u524d\u4f4d\u7f6e\u7684 <code>hashcode == MOVED == -1<\/code>,\u5219\u9700\u8981\u8fdb\u884c\u6269\u5bb9\u3002<br>5.\u5982\u679c\u90fd\u4e0d\u6ee1\u8db3\uff0c\u5219\u5229\u7528 synchronized \u9501\u5199\u5165\u6570\u636e\u3002<br>6.\u5982\u679c\u6570\u91cf\u5927\u4e8e <code>TREEIFY_THRESHOLD<\/code> \u5219\u8981\u8f6c\u6362\u4e3a\u7ea2\u9ed1\u6811\u3002<br><\/pre>\n\n\n\n<figure class=\"wp-block-image\"><img loading=\"lazy\" decoding=\"async\" width=\"597\" height=\"587\" src=\"https:\/\/www.zeroheart.xyz\/wordpress\/wp-content\/uploads\/2020\/06\/image-16.png\" alt=\"\" class=\"wp-image-868\" srcset=\"https:\/\/www.zeroheart.xyz\/wordpress\/wp-content\/uploads\/2020\/06\/image-16.png 597w, https:\/\/www.zeroheart.xyz\/wordpress\/wp-content\/uploads\/2020\/06\/image-16-300x295.png 300w\" sizes=\"(max-width: 597px) 100vw, 597px\" \/><\/figure>\n\n\n\n<p>get\u64cd\u4f5c\uff0c\u8981\u770b\u5f53\u524d\u7684\u6570\u636e\u7ed3\u6784\uff0c\u91c7\u7528\u4e0d\u540c\u7684\u65b9\u5f0f\u53d6\u503c<\/p>\n\n\n\n<ul><li>\u6839\u636e\u8ba1\u7b97\u51fa\u6765\u7684 hashcode \u5bfb\u5740\uff0c\u5982\u679c\u5c31\u5728\u6876\u4e0a\u90a3\u4e48\u76f4\u63a5\u8fd4\u56de\u503c\u3002<\/li><li>\u5982\u679c\u662f\u7ea2\u9ed1\u6811\u90a3\u5c31\u6309\u7167\u6811\u7684\u65b9\u5f0f\u83b7\u53d6\u503c\u3002<\/li><li>\u5c31\u4e0d\u6ee1\u8db3\u90a3\u5c31\u6309\u7167\u94fe\u8868\u7684\u65b9\u5f0f\u904d\u5386\u83b7\u53d6\u503c\u3002<\/li><\/ul>\n\n\n\n<p><\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u5bb9\u91cf\u8bbe\u8ba1 \u6269\u5bb9 \u5bb9\u91cf\u8bbe\u8ba1 hashmap \u9ed8\u8ba4\u5927\u5c0f\u662f2^4\uff0c\u6269\u5bb9\u662f\u6210\u500d\u7684 key\u8fdb\u884c\u53d6\u6a21\u4e4b\u540e\uff0c\u4f1a\u653e\u5230\u5bf9\u5e94\u7684in 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