\n\tCount\u662f\u88abvolatile\u6240\u4fee\u9970\uff0c\u4fdd\u8bc1\u4e86count\u7684\u53ef\u89c1\u6027\uff0c\u907f\u514d\u64cd\u4f5c\u6570\u636e\u7684\u65f6\u5019\u4ea7\u751f\u903b\u8f91\u9519\u8bef\u3002segment\u4e2d\u7684remove\u64cd\u4f5c\u548cHashMap\u5927\u81f4\u4e00\u6837\uff0cHashMap\u6ca1\u6709lock()\u548cunlock()\u64cd\u4f5c\u3002\n<\/p>\n
\n\t\u770b\u4e0bconcurrentHashMap\u7684get\u6e90\u7801\n<\/p>\n
\r\nV get(Object key, int hash) {\r\n\tif (count != 0) { \/\/ read-volatile\r\n\t\tHashEntry<K,V> e = getFirst(hash);\r\n\t\u3000\u3000\/\/\u5982\u679c\u6ca1\u6709\u627e\u5230\u5219\u76f4\u63a5\u8fd4\u56denull\r\n\t\twhile (e != null) {\r\n\t\t\tif (e.hash == hash && key.equals(e.key)) {\r\n\t\u3000\u3000\u3000\u3000\u3000\u3000\/\/\u7531\u4e8e\u6ca1\u6709\u52a0\u9501\uff0c\u5728get\u7684\u8fc7\u7a0b\u4e2d\uff0c\u53ef\u80fd\u4f1a\u6709\u66f4\u65b0\uff0c\u62ff\u5230\u7684key\u5bf9\u5e94\u7684value\u53ef\u80fd\u4e3anull\uff0c\u9700\u8981\u5355\u72ec\u5224\u65ad\u4e00\u904d\r\n\t\t\t\tV v = e.value;\r\n\t\u3000\u3000\u3000\u3000\u3000\u3000\/\/\u5982\u679cvalue\u4e3a\u4e0d\u4e3anull\uff0c\u5219\u8fd4\u56de\u83b7\u53d6\u5230\u7684value\r\n\t\t\t\tif (v != null)\r\n\t\t\t\t\treturn v;\r\n\t\t\t\treturn readValueUnderLock(e); \/\/ recheck\r\n\t\t\t}\r\n\t\t\te = e.next;\r\n\t\t}\r\n\t}\r\n\treturn null;\r\n}<\/pre>\n\n\t\u5173\u4e8econcurrentHashMap\u7684get\u7684\u76f8\u5173\u8bf4\u660e\u5df2\u7ecf\u5728\u4e0a\u9762\u4ee3\u7801\u4e2d\u7ed9\u51fa\u4e86\u6ce8\u91ca\uff0c\u8fd9\u91cc\u5c31\u4e0d\u591a\u8bf4\u4e86\u3002\n<\/p>\n
\n\t\u770b\u4e0bconcurrentHashMap\u4e2d\u7684put\n<\/p>\n
\r\npublic V put(K key, V value) {\r\n\tif (value == null)\r\n\t\tthrow new NullPointerException();\r\n\tint hash = hash(key.hashCode());\r\n\treturn segmentFor(hash).put(key, hash, value, false);\r\n}<\/pre>\n\n\t\u53ef\u4ee5\u770b\u5230concurrentHashMap\u4e0d\u5141\u8bb8key\u6216\u8005value\u4e3anull\n<\/p>\n
\n\t\u63a5\u4e0b\u6765\u770b\u4e0bsegment\u7684put\n<\/p>\n
\r\nV put(K key, int hash, V value, boolean onlyIfAbsent) {\r\n\tlock();\r\n\ttry {\r\n\t\tint c = count;\r\n\t\tif (c++ > threshold) \/\/ ensure capacity\r\n\t\t\trehash();\r\n\t\tHashEntry<K,V>[] tab = table;\r\n\t\tint index = hash & (tab.length - 1);\r\n\t\tHashEntry<K,V> first = tab[index];\r\n\t\tHashEntry<K,V> e = first;\r\n\t\twhile (e != null && (e.hash != hash || !key.equals(e.key)))\r\n\t\t\te = e.next;\r\n\r\n\t\tV oldValue;\r\n\t\tif (e != null) {\r\n\t\t\toldValue = e.value;\r\n\t\t\tif (!onlyIfAbsent)\r\n\t\t\t\te.value = value;\r\n\t\t}\r\n\t\telse {\r\n\t\t\toldValue = null;\r\n\t\t\t++modCount;\r\n\t\t\ttab[index] = new HashEntry<K,V>(key, hash, first, value);\r\n\t\t\tcount = c; \/\/ write-volatile\r\n\t\t}\r\n\t\treturn oldValue;\r\n\t} finally {\r\n\t\tunlock();\r\n\t}\r\n}<\/pre>\n\n\t\u540c\u6837\u4e5f\u662f\u52a0\u5165\u4e86\u91cd\u5165\u9501\uff0c\u5176\u4ed6\u7684\u57fa\u672c\u548cHashMap\u903b\u8f91\u5dee\u4e0d\u591a\u3002\u503c\u5f97\u4e00\u63d0\u7684\u662fjdk8\u4e2d\u6dfb\u52a0\u7684\u4e2d\u7684putval\uff0c\u8fd9\u91cc\u5c31\u4e0d\u591a\u8bf4\u4e86\u3002\n<\/p>\n
\n\t\u603b\u7ed3
\n<\/h2>\n
\n\tConcurrentHashmap\u5c06\u6570\u636e\u7ed3\u6784\u5206\u4e3a\u4e86\u591a\u4e2aSegment\uff0c\u4e5f\u662f\u4f7f\u7528\u91cd\u5165\u9501\u6765\u89e3\u51b3\u9ad8\u5e76\u53d1\uff0c\u8bb2\u4ed6\u5206\u4e3a\u591a\u4e2asegment\u662f\u4e3a\u4e86\u51cf\u5c0f\u9501\u7684\u529b\u5ea6\uff0c\u6dfb\u52a0\u7684\u65f6\u5019\u52a0\u4e86\u9501\uff0c\u7d22\u5f15\u7684\u65f6\u5019\u6ca1\u6709\u52a0\u9501\uff0c\u4f7f\u7528volatile\u4fee\u9970count\u662f\u4e3a\u4e86\u4fdd\u6301count\u7684\u53ef\u89c1\u6027\uff0c\u90fd\u662fjdk\u4e3a\u4e86\u89e3\u51b3\u5e76\u53d1\u548c\u591a\u7ebf\u7a0b\u64cd\u4f5c\u7684\u5e38\u7528\u624b\u6bb5\u3002<\/p>\n
![\"\u4e1a\u4f59\u8349\u516c\u4f17\u53f7\"\/](\"https:\/\/saas.51autoparts.cn\/api\/admin\/sys-file\/oss\/file?fileName=84db51f8561e448f9a4fda2eff0811f9.jpg\")
<\/p>
\u6700\u540e\uff0c\u6b22\u8fce\u5173\u6ce8\u6211\u7684\u4e2a\u4eba\u5fae\u4fe1\u516c\u4f17\u53f7\uff1a\u4e1a\u4f59\u8349\uff08yyucao\uff09\uff01\u53ef\u52a0\u4f5c\u8005\u5fae\u4fe1\u53f7\uff1axttblog2<\/font>\u3002\u5907\u6ce8\uff1a\u201c1\u201d\uff0c\u6dfb\u52a0\u535a\u4e3b\u5fae\u4fe1\u62c9\u4f60\u8fdb\u5fae\u4fe1\u7fa4\u3002\u5907\u6ce8\u9519\u8bef\u4e0d\u4f1a\u540c\u610f\u597d\u53cb\u7533\u8bf7\u3002<\/b>\u518d\u6b21\u611f\u8c22\u60a8\u7684\u5173\u6ce8\uff01\u540e\u7eed\u6709\u7cbe\u5f69\u5185\u5bb9\u4f1a\u7b2c\u4e00\u65f6\u95f4\u53d1\u7ed9\u60a8\uff01\u539f\u521b\u6587\u7ae0\u6295\u7a3f\u8bf7\u53d1\u9001\u81f3532009913@qq.com\u90ae\u7bb1\u3002\u5546\u52a1\u5408\u4f5c\u4e5f\u53ef\u6dfb\u52a0\u4f5c\u8005\u5fae\u4fe1\u8fdb\u884c\u8054\u7cfb\uff01<\/p>\u672c\u6587\u539f\u6587\u51fa\u5904\uff1a\u4e1a\u4f59\u8349<\/a>\uff1a » java ConcurrentHashMap \u6559\u7a0b<\/a><\/p>","protected":false},"excerpt":{"rendered":"ConcurrentHashMap\u5177\u4f53\u662f\u600e\u4e48\u5b9e\u73b0\u7ebf\u7a0b\u5b89\u5168\u7684\u5462,\u80af\u5b9a\u4e0d\u53ef\u80fd\u662f\u6bcf\u4e2a\u65b9\u6cd5\u52a0synchronized, […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[1164,1161,1334,712,1335],"class_list":["post-1597","post","type-post","status-publish","format-standard","hentry","category-java","tag-concurrenthashmap","tag-hashmap","tag-jdk8","tag-reentrantlock","tag-volatile"],"_links":{"self":[{"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/posts\/1597","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1597"}],"version-history":[{"count":1,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/posts\/1597\/revisions"}],"predecessor-version":[{"id":1598,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/posts\/1597\/revisions\/1598"}],"wp:attachment":[{"href":"https:\/\/www.xttblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1597"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1597"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1597"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}