{"id":401,"date":"2014-05-17T22:43:47","date_gmt":"2014-05-17T13:43:47","guid":{"rendered":"http:\/\/www.typea.info\/blog\/index.php\/2014\/05\/17\/java_hashcode_equals\/"},"modified":"2014-05-17T22:43:47","modified_gmt":"2014-05-17T13:43:47","slug":"java_hashcode_equals","status":"publish","type":"post","link":"https:\/\/www.typea.info\/blog\/index.php\/2014\/05\/17\/java_hashcode_equals\/","title":{"rendered":"Java \u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u306e hashCode() \u3068 equals() \u3092\u7c21\u5358\u306b\u5b9f\u88c5\u3059\u308b"},"content":{"rendered":"

\u540c\u4e00\u6027\u306e\u6bd4\u8f03\u3068\u30cf\u30c3\u30b7\u30e5\u30b3\u30fc\u30c9<\/h2>\n

Java \u30af\u30e9\u30b9\u306e equals() \u30e1\u30bd\u30c3\u30c9\u306f\u30c7\u30d5\u30a9\u30eb\u30c8\u3067\u306f\u3001\u540c\u4e00\u30a4\u30f3\u30b9\u30bf\u30f3\u30b9\u3067\u3042\u308b\u304b\u3092\u6bd4\u8f03\u3057\u3066\u3044\u308b<\/a>\u3060\u3051\u306a\u306e\u3067\u3001\u8ad6\u7406\u7684\u306b\u540c\u4e00\u3067\u3042\u308b\u304b\u3092\u6bd4\u8f03\u3059\u308b\u305f\u3081\u306b\u306f\u3001equals() \u30e1\u30bd\u30c3\u30c9\u3092\u30aa\u30fc\u30d0\u30fc\u30e9\u30a4\u30c9\u3059\u308b\u5fc5\u8981\u304c\u3042\u308b\u3002<\/p>\n

\u307e\u305f\u3001equals() \u30e1\u30bd\u30c3\u30c9\u3092\u30aa\u30fc\u30d0\u30fc\u30e9\u30a4\u30c9\u3059\u308b\u5834\u5408\u3001\u3042\u308f\u305b\u3066hashCode()\u30e1\u30bd\u30c3\u30c9\u3082\u30aa\u30fc\u30d0\u30fc\u30e9\u30a4\u30c9\u3059\u308b\u5fc5\u8981\u304c\u3042\u308b\u3002<\/p>\n

hashCode()\u306f\u3001equals()\u304c\u771f\u306b\u306a\u308b\u30a4\u30f3\u30b9\u30bf\u30f3\u30b9\u306f\u5fc5\u305a\u3001\u540c\u3058\u306b\u306a\u308b\u5024\u3092\u8fd4\u3059\u3053\u3068\u3067\u3001\u4e00\u81f4\u3059\u308b\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u63a2\u3057\u3084\u3059\u304f\u3059\u308b\u5f79\u76ee\u3092\u679c\u305f\u3059\u3002\u4f8b\u3048\u3070\u3001\u5b66\u7c4d\u756a\u53f7\u3092\u3001\u767e\u756a\u53f0\u3067\u5206\u3051\u308b\u3053\u3068\u306b\u3088\u308a\u3001\u305d\u306e\u30b0\u30eb\u30fc\u30d7\u306e\u4e2d\u3092\u63a2\u305b\u3070\u52b9\u7387\u304c\u3088\u304f\u306a\u308b\u3088\u3046\u306b\u3002<\/p>\n\n\n\n\n\n\n
\u5b66\u7c4d\u756a\u53f7(ID)<\/td>\n\u5b66\u7c4d\u756a\u53f7\u30b0\u30eb\u30fc\u30d7(\u30cf\u30c3\u30b7\u30e5\u30b3\u30fc\u30c9)<\/td>\n<\/tr>\n
001 \uff5e 099<\/td>\n0<\/td>\n<\/tr>\n
101 \uff5e 199<\/td>\n1<\/td>\n<\/tr>\n
201 \uff5e 299<\/td>\n2<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/p>\n

\u4e0a\u8a18\u306e\u4f8b\u306e\u3088\u3046\u306b\u3001\u5b66\u7c4d\u756a\u53f7\u30b0\u30eb\u30fc\u30d7(\u30cf\u30c3\u30b7\u30e5\u30b3\u30fc\u30c9) \u3054\u3068\u306b\u30b0\u30eb\u30fc\u30d7(\u30d0\u30b1\u30c4)\u3092\u4f5c\u6210\u3057\u3001\u305d\u306e\u4e2d\u306b\u5b66\u7c4d\u756a\u53f7\u304c\u8868\u3059\u5b9f\u614b(\u30a4\u30f3\u30b9\u30bf\u30f3\u30b9)\u3092\u5165\u308c\u3066\u304a\u3051\u3070\u3001\u4f8b\u3048\u3070\u3001\u5b66\u7c4d\u756a\u53f7 222 \u306e\u30a4\u30f3\u30b9\u30bf\u30f3\u30b9\u3092\u898b\u3064\u3051\u308b\u306b\u306f\u3001\u5b66\u7c4d\u756a\u53f7\u30b0\u30eb\u30fc\u30d7(\u30cf\u30c3\u30b7\u30e5\u30b3\u30fc\u30c9) 2 \u306e\u30d0\u30b1\u30c4\u306e\u4e2d\u3060\u3051\u63a2\u305b\u3070\u3088\u3044\u3002<\/p>\n

\u30cf\u30c3\u30b7\u30e5\u30b3\u30fc\u30c9\u3068\u306f\u3001\u3042\u308b\u30c7\u30fc\u30bf\u304c\u4e0e\u3048\u3089\u308c\u305f\u3068\u304d\u306b\u3001\u5e38\u306b\u540c\u3058\u5024\u3092\u8fd4\u3059(\u30cf\u30c3\u30b7\u30e5\u95a2\u6570<\/a>)\u3092\u7d4c\u3066\u3048\u3089\u308c\u305f\u5024\u306e\u3053\u3068\u306a\u306e\u3067\u3001\u6975\u7aef\u306b\u8a00\u3046\u3068\u3001\u5e38\u306b\u4e00\u5b9a\u306e\u5024\u3092\u8fd4\u3057\u3066\u3082\u3001\u201d\u9593\u9055\u3044"\u3067\u306f\u306a\u3044\u304c\u3001\u52b9\u7387\u304c\u60aa\u3044\u306e\u306f\u3001\u4e0a\u8a18\u306e\u4f8b\u3067\u8a00\u3048\u3070\u3001222 \u306e\u30a4\u30f3\u30b9\u30bf\u30f3\u30b9\u3092\u898b\u3064\u3051\u308b\u305f\u3081\u306b\u3001\u5168\u6821\u751f\u5f92\u3092\u5148\u982d\u304b\u3089\u63a2\u3055\u306a\u3051\u308c\u3070\u3044\u3051\u306a\u3044\u3053\u3068\u304b\u3089\u3001\u60f3\u50cf\u3064\u304f\u3060\u308d\u3046\u3002<\/p>\n

Java\u30af\u30e9\u30b9\u306b\u5b9f\u88c5\u3059\u308b\u3001\u30cf\u30c3\u30b7\u30e5\u30b3\u30fc\u30c9\u306f\u3001HashMap \u306a\u3069\u3001\u30a4\u30f3\u30b9\u30bf\u30f3\u30b9\u7ba1\u7406\u306e\u57fa\u672c\u306b\u306a\u308b\u306e\u3067\u3001\u5024\u304c\u3070\u3089\u3051\u3066\u683c\u7d0d\u3055\u308c\u305f\u65b9\u304c\u52b9\u7387\u304c\u3088\u304b\u3063\u305f\u308a\u3068\u4f5c\u6210\u306e\u4ed5\u65b9\u306b\u3088\u3063\u3066\u3001\u52b9\u7387\u304c\u5909\u308f\u3063\u3066\u304f\u308b\u3002<\/p>\n

\u306a\u30fc\u3093\u3066\u3001\u7406\u5c48\u306f\u308f\u304b\u3063\u3066\u3044\u3066\u3082\u3001\u5177\u4f53\u7684\u306b\u306f\u3069\u3046\u5b9f\u88c5\u3057\u305f\u3089\u3044\u3044\u3093\u3060\u3088\uff5e\"\"<\/p>\n

\u3068\u3044\u3046\u5fa1\u4ec1\u306b\u306f\u3001Effective Java \u7b2c2\u7248 (The Java Series)<\/a>\"\"  \u3092\u4e00\u8aad\u3059\u308b\u3053\u3068\u3092\u304a\u52e7\u3081\u3059\u308b\u3002<\/p>\n

<\/a><\/p>\n

\u4e00\u90e8\u8981\u7d04\u3059\u308b\u3068\u3001<\/p>\n

equals \u3092\u30aa\u30fc\u30d0\u30fc\u30e9\u30a4\u30c9\u3059\u308b\u3068\u304d\u306f\u4e00\u822c\u5951\u7d04\u306b\u5f93\u3046<\/h3>\n

\u4e00\u822c\u5951\u7d04<\/p>\n\n\n\n\n\n\n\n
\u5951\u7d04<\/td>\n\u5185\u5bb9<\/td>\n<\/tr>\n
\u53cd\u5c04\u7684<\/td>\nx.equals(x) \u306f true<\/td>\n<\/tr>\n
\u5bfe\u79f0\u7684<\/td>\ny.equals(x) \u304c true \u306e\u5834\u5408\u306e\u307f\u3001x.equals(y) \u3082 true<\/td>\n<\/tr>\n
\u63a8\u79fb\u7684<\/td>\nx.equals(y) \u3001y.equals(z) \u304c true \u306a\u3089\u3070\u3001x.equals(z) \u3082 true<\/td>\n<\/tr>\n
\u6574\u5408\u7684<\/td>\n\u60c5\u5831\u304c\u5909\u66f4\u3055\u308c\u306a\u3051\u308c\u3070\u3001x.equals(y) \u306e\u7d50\u679c\u306f\u4e0d\u5909<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/p>\n

\n

\u62bd\u8c61\u5316\u306e\u6069\u6075\u3092\u3042\u304d\u3089\u3081\u305a\u306b\u3001\u30a4\u30f3\u30b9\u30bf\u30f3\u30b9\u5316\u53ef\u80fd\u306a\u30af\u30e9\u30b9\u3092\u62e1\u5f35\u3057\u3066\u3001equals \u5951\u7d04\u3092\u5b88\u3063\u305f\u307e\u307e\u3001\u5024\u8981\u7d20\u3092\u8ffd\u52a0\u3059\u308b\u65b9\u6cd5\u306f\u306a\u3044\u3002<\/p>\n<\/blockquote>\n

equals \u3092\u30aa\u30fc\u30d0\u30fc\u30e9\u30a4\u30c9\u3059\u308b\u6642\u306f\u3001\u5e38\u306b hashCode \u3092\u30aa\u30fc\u30d0\u30fc\u30e9\u30a4\u30c9\u3059\u308b<\/h3>\n
    \n
  1. \u30bc\u30ed\u3067\u306f\u306a\u3044\u5b9a\u6570(\u305f\u3068\u3048\u307017)\u3092 result(int\u578b)\u306b\u4fdd\u5b58 <\/li>\n
  2. \u610f\u5473\u306e\u3042\u308b\u30d5\u30a3\u30fc\u30eb\u30c9\u306b\u5bfe\u3057\u3066\u3001\u6b21\u3092\u884c\u3046\n
      \n
    1. boolean \u306a\u3089 (f?1:0) <\/li>\n
    2. byte,char,short,int \u306a\u3089\u3001(int)f <\/li>\n
    3. long \u306a\u3089\u3001(int)(f^(f>>32)) <\/li>\n
    4. float \u306a\u3089\u3001Float.floatToIntBits(f) <\/li>\n
    5. double \u306a\u3089\u3001Double.doubleToLongBits(f) \u3092\u884c\u3044\u3001long \u3068\u540c\u69d8\u306e\u5909\u63db <\/li>\n
    6. \u53c2\u7167\u306a\u3089\u3001\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u306ehashCode() null \u306a\u3089 0 <\/li>\n
    7. \u914d\u5217\u306a\u3089\u3001\u5404\u8981\u7d20\u3092 \u30d5\u30a3\u30fc\u30eb\u30c9\u3068\u3057\u3066\u6271\u3046 <\/li>\n
    8. result = 31 * result + c \/\/ c=\u8a08\u7b97\u3055\u308c\u305f\u30cf\u30c3\u30b7\u30e5\u30b3\u30fc\u30c9 <\/li>\n<\/ol>\n<\/li>\n<\/ol>\n
      public int hashCode() {\r\n  int result = 17;\r\n  result = 31 * result + foo;\r\n  result = 31 * result + bar;\r\n  return result;  \r\n}<\/pre>\n
       <\/p>\n
      equals() \u3001hashCode() \u3092\u30aa\u30fc\u30d0\u30fc\u30e9\u30a4\u30c9\u3059\u308b\u7c21\u5358\u306a\u65b9\u6cd5<\/h2>\n
      \u3068\u3044\u3046\u3088\u3046\u306a\u3053\u3068\u3067\u3001equals()\u3092\u30aa\u30fc\u30d0\u30fc\u30e9\u30a4\u30c9\u3059\u308b\u5fc5\u8981\u304c\u3042\u308b\u5834\u5408\u306a\u3069\u306f\u3001Effective Java<\/a>\"\" \u306e\u30e1\u30e2<\/a>\u3092\u78ba\u8a8d\u3057\u306a\u304c\u3089\u5b9f\u88c5\u3057\u3066\u304d\u305f\u3002\u3002\u3002\u4eca\u65e5\u307e\u3067\u306f\u3002<\/p>\n
      \u3057\u304b\u3057\u3001\u306a\u3001\u306a\u3093\u3068<\/p>\n
      \"equals_and_hashcode_implement\"<\/a><\/p>\n
      Eclipse \u3067Java\u30af\u30e9\u30b9\u3092\u9078\u629e\u3057\u3001\u30b3\u30f3\u30c6\u30ad\u30b9\u30c8\u30e1\u30cb\u30e5\u30fc\u304b\u3089\u3001Source \u2013 Generate hashCode() and equals() \u3092\u5b9f\u884c\u3059\u308b\u3068\u3002\u3002\u3002<\/p>\n
      @Override\r\nprivate Long id;\r\nprivate String name;\r\nprivate String email;\r\nprivate String phoneNumber;\r\n\r\npublic int hashCode() {\r\n    final int prime = 31;\r\n    int result = 1;\r\n    result = prime * result + ((email == null) ? 0 : email.hashCode());\r\n    result = prime * result + ((id == null) ? 0 : id.hashCode());\r\n    result = prime * result + ((name == null) ? 0 : name.hashCode());\r\n    result = prime * result\r\n            + ((phoneNumber == null) ? 0 : phoneNumber.hashCode());\r\n    return result;\r\n}\r\n\r\n@Override\r\npublic boolean equals(Object obj) {\r\n    if (this == obj)\r\n        return true;\r\n    if (obj == null)\r\n        return false;\r\n    if (getClass() != obj.getClass())\r\n        return false;\r\n    Member other = (Member) obj;\r\n    if (email == null) {\r\n        if (other.email != null)\r\n            return false;\r\n    } else if (!email.equals(other.email))\r\n        return false;\r\n    if (id == null) {\r\n        if (other.id != null)\r\n            return false;\r\n    } else if (!id.equals(other.id))\r\n        return false;\r\n    if (name == null) {\r\n        if (other.name != null)\r\n            return false;\r\n    } else if (!name.equals(other.name))\r\n        return false;\r\n    if (phoneNumber == null) {\r\n        if (other.phoneNumber != null)\r\n            return false;\r\n    } else if (!phoneNumber.equals(other.phoneNumber))\r\n        return false;\r\n    return true;\r\n}<\/pre>\n
      \u3053\u3093\u306a\u611f\u3058\u3067\u3001\u4e21\u30e1\u30bd\u30c3\u30c9\u304c\u3001\u81ea\u52d5\u751f\u6210\u3055\u308c\u308b\u3084\u306a\u3044\u304b\u30fc\u30fc\u30fc\u3044\u3002<\/p>\n
      \u3057\u3089\u3093\u304b\u3063\u305f\u3002\u3002\u3002<\/p>\n
      \u4ed6\u306b\u3082\u3001Constructor using fields \u3068\u304b\u3042\u308b\u3057\u3002\u3002\u3002<\/p>\n
      \u3044\u3064\u3082\u306f\u3001\u30a2\u30af\u30bb\u30c3\u30b5\u30fc\u4f5c\u6210\u3057\u305f\u308a\u3001toString() \u5b9f\u88c5\u3057\u305f\u308a\u6307\u7656\u3068\u3044\u3046\u304b\u6761\u4ef6\u53cd\u5c04\u3067\u3084\u3063\u3066\u3044\u305f\u306e\u3067\u3001\u3069\u3093\u306a\u3053\u3068\u304c\u51fa\u6765\u308b\u304b\u3042\u307e\u308a\u9867\u307f\u3066\u306a\u304b\u3063\u305f\u306a\u30fc<\/p>\n
      \u53cd\u7701\u3002<\/p>\n
       <\/p>\n
      Java \u5b9f\u88c5\u306e\u6307\u91dd\u3092\u4e0e\u3048\u3066\u304f\u308c\u308b\u826f\u66f8\uff01\u304a\u3059\u3059\u3081!<\/p>\n