Blog \u30a8\u30f3\u30c8\u30ea\u30fc\u3055\u307c\u308a\u304c\u3061\u306b\u306a\u308b\u306e\u3067\u3057\u3087\u3046\u3082\u306a\u3044\u30cd\u30bf\u3092\u66f8\u3044\u3068\u304d\u307e\u3059\u3002<\/p>\n
Java 8 \u306b\u306a\u3063\u3066 Stream API \u304c\u3081\u3063\u3061\u3083\u4fbf\u5229\u306b\u4f7f\u3048\u3066\u3088\u308d\u3053\u3093\u3067\u3044\u308b\u958b\u767a\u8005\u305f\u3061\u304c\u305f\u304f\u3055\u3093\u3044\u307e\u3059\u3088\u306d\uff01<\/p>\n
\u4e2d\u306b\u306f\u4ed5\u4e8b\u3067\u672a\u3060\u306b\u53e4\u3044 Java \u3092\u4f7f\u308f\u3056\u308b\u3092\u5f97\u306a\u3044\u975e\u5e38\u306b\u53ef\u611b\u305d\u3046\u306a\u74b0\u5883\u306e\u3072\u3068\u3082\u30fb\u30fb\u30fb\uff08\u30f2\u30d2<\/p>\n
\u3067\u3001\u304a\u305d\u3089\u304f\u6625\u306b\u5165\u793e\u3057\u3066\u304f\u308b\u30d5\u30ec\u30c3\u30b7\u30e5\u306a\u65b0\u4eba\u30d7\u30ed\u30b0\u30e9\u30de\u306b\u306f Java 8 \u306e Stream API \u3092\u4f7f\u3063\u305f\u65b0\u3057\u3044\u69cb\u6587\u3092\u52c9\u5f37\u3057\u3066\u3082\u3089\u3046\u3053\u3068\u306b\u306a\u308a\u307e\u3059\u3088\u306d\uff1f<\/p>\n
\u4eca\u3055\u3089\u3001JDK 1.4, JDK 1.5, JDK1.6, JDK1.7 \u306a\u3093\u3066\u3053\u3068\u306f\u306a\u3044\u3067\u3059\u3088\u306d\u3002\u306d\u3063\uff01\u306d\u3063\uff01<\/p>\n
\u305d\u3053\u3067\u30011 \u304b\u3089 1000 \u307e\u3067\u306e\u5076\u6570\u3060\u3051\u306e\u7dcf\u548c\u3092\u6c42\u3081\u3002<\/p>\n
2 \u306e 0 \u4e57\u304b\u3089 2 \u306e 32 \u4e57\u307e\u3067\u306e\u7dcf\u548c\u3092\u6c42\u3081\u308b\u3002<\/p>\n
\u3053\u306e\u4e8c\u3064\u3092\u984c\u6750\u306b\u3057\u3066\u8d85\u30b7\u30f3\u30d7\u30eb\u306a\u30d7\u30ed\u30b0\u30e9\u30e0\u3092 Java 8 \u3067\u7d44\u3080\u3068\u3069\u3046\u306a\u308b\u3067\u3057\u3087\u3046\u304b\uff1f<\/p>\n
\u6b21\u306e\u3088\u3046\u306a\u611f\u3058\u3067\u7d44\u3093\u3067\u3057\u307e\u3063\u305f\u3089\u3001\u3042\u306a\u305f\u306f\u65b0\u4eba\u3055\u3093\u306b\u5f71\u3067 static \u304a\u3058\u3055\u3093\u3000\u3058\u3083\u306a\u3044\u30fb\u30fb\u30fb\u3000Stream \u304a\u3058\u3055\u3093 \u3068\u547c\u3070\u308c\u308b\u3053\u3068\u306b\u306a\u308b\u304b\u3082\u3057\u308c\u307e\u305b\u3093\u3002<\/p>\n
\r\npackage jp.yucchi.bad.summation;\r\n\r\nimport java.util.stream.DoubleStream;\r\nimport java.util.stream.IntStream;\r\n\r\n\/**\r\n *\r\n * @author Yucchi\r\n *\/\r\npublic class BadSummation {\r\n\r\n public static void main(String[] args) {\r\n\r\n \/\/ 1 \u304b\u3089 1000 \u307e\u3067\u306e\u5076\u6570\u3060\u3051\u306e\u7dcf\u548c\u3092\u6c42\u3081\u308b\u3002\r\n int sum = IntStream.rangeClosed(1, 1_000)\r\n .filter(e -> (e & 1) == 0)\r\n .sum();\r\n\r\n System.out.println(\"1 \u304b\u3089 1000 \u307e\u3067\u306e\u5076\u6570\u3060\u3051\u306e\u7dcf\u548c\u306f\u3001\" + sum + \" \u3067\u3059\u3002\");\r\n \r\n\r\n \/\/ 2 \u306e 0 \u4e57\u304b\u3089 2 \u306e 32 \u4e57\u307e\u3067\u306e\u7dcf\u548c\u3092\u6c42\u3081\u308b\u3002\r\n double powerSum = DoubleStream.iterate(0.0, i -> i + 1.0)\r\n .limit(32 + 1)\r\n .map(i -> Math.pow(2.0, i))\r\n .sum();\r\n\r\n System.out.println(\"2 \u306e 0 \u4e57\u304b\u3089 2 \u306e 32 \u4e57\u307e\u3067\u306e\u7dcf\u548c\u306f\u3001\" + powerSum + \" \u3067\u3059\u3002\");\r\n }\r\n\r\n}\r\n<\/pre>\n<\/p>\n\u3048\u3063\uff1f<\/p>\n
\u3053\u3093\u306a\u611f\u3058\u306e\u30d7\u30ed\u30b0\u30e9\u30e0\u3057\u304b\u601d\u3044\u3046\u304b\u3070\u306a\u3044\u3063\u3066\uff01<\/p>\n
Stream \u304a\u3058\u3055\u3093 \u306b\u8a8d\u5b9a\u3057\u307e\u3059\uff01<\/p>\n
\u3053\u306e\u30d7\u30ed\u30b0\u30e9\u30e0\u306f Stream API \u306e\u8aac\u660e\u30b5\u30f3\u30d7\u30eb\u306b\u306f\u554f\u984c\u306a\u3044\u306e\u3067\u3059\u304c\u52b9\u7387\u304c\u60aa\u3044\u306e\u3067\u3059\u3002<\/p>\n
\u307e\u3058\u3081\u306b\u52c9\u5f37\u3092\u3057\u3066\u304d\u305f\u65b0\u4eba\u3055\u3093\u307b\u3069\u3053\u3046\u3044\u3063\u305f\u3068\u3053\u308d\u3092\u7a81\u3044\u3066\u304f\u308b\u3068\u601d\u3046\u306e\u3067\u5148\u306b\u53e4\u5178\u7684\u306a\u624b\u6cd5\u3067\u6c42\u3081\u308b\u65b9\u6cd5\u3092\u898b\u305b\u3068\u3044\u3066\u304b\u3089<\/p>\n
\u7121\u7406\u306b Stream API \u3092\u4f7f\u3046\u3068\u3053\u3046\u306a\u308b\u3088\u3063\u3066\u8a00\u3063\u3068\u304f\u306e\u304c\u7121\u96e3\u3060\u3068\u601d\u3044\u307e\u3059\u3002<\/p>\n
\u65b0\u4eba\u30d7\u30ed\u30b0\u30e9\u30de\u306e\u591a\u304f\u306f\u6b21\u306e\u3088\u3046\u306a\u30d7\u30ed\u30b0\u30e9\u30e0\u3092\u5f53\u305f\u308a\u524d\u306e\u3088\u3046\u306b\u7d44\u3080\u3067\u3057\u3087\u3046\u3002<\/p>\n
Stream API \u306a\u3093\u3066\u4f7f\u308f\u305a\u306b\u53e4\u5178\u7684\u306a\u624b\u6cd5\u3092\u7528\u3044\u3066\u30b7\u30f3\u30d7\u30eb\u306b\uff01<\/p>\n
\r\npackage jp.yucchi.summation;\r\n\r\n\/**\r\n *\r\n * @author Yucchi\r\n *\/\r\npublic class Summation {\r\n\r\n public static void main(String[] args) {\r\n\r\n \/\/ 1 \u304b\u3089 1000 \u307e\u3067\u306e\u5076\u6570\u3060\u3051\u306e\u7dcf\u548c\u3092\u6c42\u3081\u308b\u3002\r\n int sum = 1_000 \/ 2 * (1_000 \/ 2 + 1);\r\n\r\n System.out.println(\"1 \u304b\u3089 1000 \u307e\u3067\u306e\u5076\u6570\u3060\u3051\u306e\u7dcf\u548c\u306f\u3001\" + sum + \" \u3067\u3059\u3002\");\r\n \r\n\r\n \/\/ 2 \u306e 0 \u4e57\u304b\u3089 2 \u306e 32 \u4e57\u307e\u3067\u306e\u7dcf\u548c\u3092\u6c42\u3081\u308b\u3002\r\n double powerSum = Math.pow(2.0, 32.0 + 1.0) - 1.0;\r\n\r\n System.out.println(\"2 \u306e 0 \u4e57\u304b\u3089 2 \u306e 32 \u4e57\u307e\u3067\u306e\u7dcf\u548c\u306f\u3001\" + powerSum + \" \u3067\u3059\u3002\");\r\n\r\n }\r\n\r\n}\r\n<\/pre>\n<\/p>\n\u3044\u3064\u306e\u6642\u4ee3\u306b\u306a\u3063\u3066\u3082\u3053\u3046\u3044\u3063\u305f\u5b9a\u756a\u306e\u51e6\u7406\u65b9\u6cd5\u306f\u4e0d\u6ec5\u3067\u3059\uff01<\/p>\n
\u3061\u306a\u307f\u306b\u5076\u6570\u306e\u7dcf\u548c\u306f\u300c\u65e5\u7d4c\u30bd\u30d5\u30c8\u30a6\u30a7\u30a2\uff13\u6708\u53f7\u300d\u306e\u300c\u30a2\u30eb\u30b4\u30ea\u30ba\u30e0\uff06\u30c6\u30af\u30cb\u30c3\u30af\u300d\u3067\u7d39\u4ecb\u3055\u308c\u3066\u307e\u3059\u3002<\/p>\n
\u4eca\u6708\u306f\u4ed6\u306b\u3082\u9762\u767d\u30cd\u30bf\u304c\u7d39\u4ecb\u3055\u308c\u3066\u3044\u3066\u304a\u3082\u3057\u308d\u304b\u3063\u305f\u3002<\/p>\n