“`”<\/p>\n
<ol><li><strong>\u7ebf\u7a0b\u662f\u5426\u5b89\u5168\uff1a<\/strong> HashMap \u662f\u975e\u7ebf\u7a0b\u5b89\u5168\u7684\uff0cHashTable \u662f\u7ebf\u7a0b\u5b89\u5168\u7684\uff1bHashTable \u5185\u90e8\u7684\u65b9\u6cd5\u57fa\u672c\u90fd\u7ecf\u8fc7<code>synchronized<\/code> \u4fee\u9970\u3002\uff08\u5982\u679c\u4f60\u8981\u4fdd\u8bc1\u7ebf\u7a0b\u5b89\u5168\u7684\u8bdd\u5c31\u4f7f\u7528 ConcurrentHashMap \u5427\uff01\uff09\uff1b<\/li><li><strong>\u6548\u7387\uff1a<\/strong> \u56e0\u4e3a\u7ebf\u7a0b\u5b89\u5168\u7684\u95ee\u9898\uff0cHashMap \u8981\u6bd4 HashTable \u6548\u7387\u9ad8\u4e00\u70b9\u3002\u53e6\u5916\uff0cHashTable \u57fa\u672c\u88ab\u6dd8\u6c70\uff0c\u4e0d\u8981\u5728\u4ee3\u7801\u4e2d\u4f7f\u7528\u5b83\uff1b<\/li><li><strong>\u5bf9Null key \u548cNull value\u7684\u652f\u6301\uff1a<\/strong> HashMap \u4e2d\uff0cnull \u53ef\u4ee5\u4f5c\u4e3a\u952e\uff0c\u8fd9\u6837\u7684\u952e\u53ea\u6709\u4e00\u4e2a\uff0c\u53ef\u4ee5\u6709\u4e00\u4e2a\u6216\u591a\u4e2a\u952e\u6240\u5bf9\u5e94\u7684\u503c\u4e3a null\u3002\u3002\u4f46\u662f\u5728 HashTable \u4e2d put \u8fdb\u7684\u952e\u503c\u53ea\u8981\u6709\u4e00\u4e2a null\uff0c\u76f4\u63a5\u629b\u51fa NullPointerException\u3002<\/li><li><strong>\u521d\u59cb\u5bb9\u91cf\u5927\u5c0f\u548c\u6bcf\u6b21\u6269\u5145\u5bb9\u91cf\u5927\u5c0f\u7684\u4e0d\u540c \uff1a<\/strong> \u2460\u521b\u5efa\u65f6\u5982\u679c\u4e0d\u6307\u5b9a\u5bb9\u91cf\u521d\u59cb\u503c\uff0cHashtable \u9ed8\u8ba4\u7684\u521d\u59cb\u5927\u5c0f\u4e3a11\uff0c\u4e4b\u540e\u6bcf\u6b21\u6269\u5145\uff0c\u5bb9\u91cf\u53d8\u4e3a\u539f\u6765\u76842n+1\u3002HashMap \u9ed8\u8ba4\u7684\u521d\u59cb\u5316\u5927\u5c0f\u4e3a16\u3002\u4e4b\u540e\u6bcf\u6b21\u6269\u5145\uff0c\u5bb9\u91cf\u53d8\u4e3a\u539f\u6765\u76842\u500d\u3002\u2461\u521b\u5efa\u65f6\u5982\u679c\u7ed9\u5b9a\u4e86\u5bb9\u91cf\u521d\u59cb\u503c\uff0c\u90a3\u4e48 Hashtable \u4f1a\u76f4\u63a5\u4f7f\u7528\u4f60\u7ed9\u5b9a\u7684\u5927\u5c0f\uff0c\u800c HashMap \u4f1a\u5c06\u5176\u6269\u5145\u4e3a2\u7684\u5e42\u6b21\u65b9\u5927\u5c0f\uff08HashMap \u4e2d\u7684<code>tableSizeFor()<\/code>\u65b9\u6cd5\u4fdd\u8bc1\uff0c\u4e0b\u9762\u7ed9\u51fa\u4e86\u6e90\u4ee3\u7801\uff09\u3002\u4e5f\u5c31\u662f\u8bf4 HashMap \u603b\u662f\u4f7f\u75282\u7684\u5e42\u4f5c\u4e3a\u54c8\u5e0c\u8868\u7684\u5927\u5c0f,\u540e\u9762\u4f1a\u4ecb\u7ecd\u5230\u4e3a\u4ec0\u4e48\u662f2\u7684\u5e42\u6b21\u65b9\u3002<\/li><li><strong>\u5e95\u5c42\u6570\u636e\u7ed3\u6784\uff1a<\/strong> JDK1.8 \u4ee5\u540e\u7684 HashMap \u5728\u89e3\u51b3\u54c8\u5e0c\u51b2\u7a81\u65f6\u6709\u4e86\u8f83\u5927\u7684\u53d8\u5316\uff0c\u5f53\u94fe\u8868\u957f\u5ea6\u5927\u4e8e\u9608\u503c\uff08\u9ed8\u8ba4\u4e3a8\uff09\u65f6\uff0c\u5c06\u94fe\u8868\u8f6c\u5316\u4e3a\u7ea2\u9ed1\u6811\uff0c\u4ee5\u51cf\u5c11\u641c\u7d22\u65f6\u95f4\u3002Hashtable \u6ca1\u6709\u8fd9\u6837\u7684\u673a\u5236\u3002<\/li><\/ol><\/p>\n
<strong>HashMap \u4e2d\u5e26\u6709\u521d\u59cb\u5bb9\u91cf\u7684\u6784\u9020\u51fd\u6570\uff1a<\/strong><\/p>\n
<pre><code>java public HashMap(int initialCapacity, float loadFactor) { if (initialCapacity < 0) throw new IllegalArgumentException(""Illegal initial capacity: "" + initialCapacity); if (initialCapacity > MAXIMUM_CAPACITY) initialCapacity = MAXIMUM_CAPACITY; if (loadFactor <= 0 || Float.isNaN(loadFactor)) throw new IllegalArgumentException(""Illegal load factor: "" + loadFactor); this.loadFactor = loadFactor; this.threshold = tableSizeFor(initialCapacity); } public HashMap(int initialCapacity) { this(initialCapacity, DEFAULT_LOAD_FACTOR); }<\/code><\/pre><\/p>\n
\u4e0b\u9762\u8fd9\u4e2a\u65b9\u6cd5\u4fdd\u8bc1\u4e86 HashMap \u603b\u662f\u4f7f\u75282\u7684\u5e42\u4f5c\u4e3a\u54c8\u5e0c\u8868\u7684\u5927\u5c0f\u3002<\/p>\n
<pre><code>java \/** * Returns a power of two size for the given target capacity. *\/ static final int tableSizeFor(int cap) { int n = cap – 1; n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8; n |= n >>> 16; return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1; }<\/code><\/pre><\/p>\n
<pre><code> "“`
\n<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"
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