{"id":930,"date":"2022-10-19T17:52:58","date_gmt":"2023-10-17T19:29:24","guid":{"rendered":"https:\/\/www.silicloud.com\/ja\/blog\/index.php\/2023\/11\/30\/java-stream%e3%81%aecollect%e3%83%a1%e3%82%bd%e3%83%83%e3%83%89%e3%81%ae%e4%be%8b\/"},"modified":"2025-08-01T03:37:41","modified_gmt":"2025-07-31T18:37:41","slug":"java-stream%e3%81%aecollect%e3%83%a1%e3%82%bd%e3%83%83%e3%83%89%e3%81%ae%e4%be%8b","status":"publish","type":"post","link":"https:\/\/www.silicloud.com\/ja\/blog\/java-stream%e3%81%aecollect%e3%83%a1%e3%82%bd%e3%83%83%e3%83%89%e3%81%ae%e4%be%8b\/","title":{"rendered":"Java Stream\u306ecollect()\u30e1\u30bd\u30c3\u30c9\u306e\u4f8b"},"content":{"rendered":"

Java Stream\u306ecollect()\u306f\u3001\u30b9\u30c8\u30ea\u30fc\u30e0\u306e\u8981\u7d20\u306b\u5bfe\u3057\u3066\u53ef\u5909\u306e\u96c6\u7d04\u64cd\u4f5c\u3092\u5b9f\u884c\u3057\u307e\u3059\u3002\u3053\u306e\u64cd\u4f5c\u306f\u7d42\u7aef\u64cd\u4f5c\u3067\u3059\u3002<\/p>\n

\u53ef\u5909\u524a\u6e1b\u64cd\u4f5c\u3068\u306f\u4f55\u3067\u3059\u304b\uff1f (Kahen saku gen s\u014dsa to wa nanidesu ka?)<\/h2>\n

\u53ef\u5909\u524a\u6e1b\u64cd\u4f5c\u306f\u3001\u30b9\u30c8\u30ea\u30fc\u30e0\u8981\u7d20\u3092\u51e6\u7406\u3057\u3001\u305d\u308c\u3092\u53ef\u5909\u306e\u7d50\u679c\u30b3\u30f3\u30c6\u30ca\u306b\u84c4\u7a4d\u3057\u307e\u3059\u3002\u8981\u7d20\u304c\u51e6\u7406\u3055\u308c\u308b\u3068\u3001\u7d50\u679c\u30b3\u30f3\u30c6\u30ca\u3092\u7d50\u5408\u3059\u308b\u7d50\u5408\u95a2\u6570\u304c\u5b58\u5728\u3057\u3001\u305d\u308c\u306b\u3088\u3063\u3066\u7d50\u679c\u304c\u4f5c\u6210\u3055\u308c\u307e\u3059\u3002<\/p>\n

Java\u306eStream collect()\u30e1\u30bd\u30c3\u30c9\u306e\u30b7\u30b0\u30cd\u30c1\u30e3\u3092\u65e5\u672c\u8a9e\u3067\u66f8\u304d\u63db\u3048\u308b\u3068\u3001\u4ee5\u4e0b\u306e\u3088\u3046\u306b\u306a\u308a\u307e\u3059\u3002<\/h2>\n

Java Stream\u306ecollect()\u30e1\u30bd\u30c3\u30c9\u306b\u306f2\u3064\u306e\u30d0\u30ea\u30a2\u30f3\u30c8\u304c\u3042\u308a\u307e\u3059\u3002<\/p>\n

    \n
  1. \n
      R collect(Supplier supplier, BiConsumer<R, ? super T> accumulator,BiConsumer<R, R> combiner) can be paraphrased as:<\/ol>\n<\/li>\n<\/ol>\n

       <\/p>\n

        R collect(Supplier supplier, BiConsumer<R, ? super T> accumulator, BiConsumer<R, R> combiner)\u3092\u5225\u306e\u8a00\u3044\u65b9\u306b\u3059\u308b\u3068\u3001\u4ee5\u4e0b\u306e\u3088\u3046\u306b\u306a\u308a\u307e\u3059\uff1a<\/ol>\n

        \u30b3\u30ec\u30af\u30bf\u30fc\u306f\u3001\u4f9b\u7d66\u8005\u3001\u84c4\u7a4d\u5668\u3001\u304a\u3088\u3073\u7d50\u5408\u5668\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u306e\u305f\u3081\u306e\u30e9\u30c3\u30d1\u30fc\u3092\u63d0\u4f9b\u3059\u308b\u30a4\u30f3\u30bf\u30fc\u30d5\u30a7\u30fc\u30b9\u3067\u3059\u30022\u756a\u76ee\u306e\u30e1\u30bd\u30c3\u30c9\u306f\u3001\u30d3\u30eb\u30c8\u30a4\u30f3\u306e\u30b3\u30ec\u30af\u30bf\u30fc\u5b9f\u88c5\u3092\u63d0\u4f9b\u3059\u308b\u305f\u3081\u306bCollectors\u30af\u30e9\u30b9\u3092\u5229\u7528\u3059\u308b\u5834\u5408\u306b\u4fbf\u5229\u3067\u3059\u3002collect()\u95a2\u6570\u306e3\u3064\u306e\u30d1\u30e9\u30e1\u30fc\u30bf\u306f\u6b21\u306e\u3068\u304a\u308a\u3067\u3059\u3002<\/p>\n

          \n
        1. \n
            \u30b5\u30d7\u30e9\u30a4\u30e4\u30fc\uff1a\u65b0\u3057\u3044\u53ef\u5909\u306e\u7d50\u679c\u30b3\u30f3\u30c6\u30ca\u3092\u4f5c\u6210\u3059\u308b\u6a5f\u80fd\u3002\u4e26\u5217\u5b9f\u884c\u3067\u306f\u3001\u3053\u306e\u95a2\u6570\u306f\u8907\u6570\u56de\u547c\u3073\u51fa\u3055\u308c\u308b\u53ef\u80fd\u6027\u304c\u3042\u308a\u3001\u5404\u547c\u3073\u51fa\u3057\u3067\u65b0\u3057\u3044\u5024\u3092\u8fd4\u3055\u306a\u3051\u308c\u3070\u306a\u308a\u307e\u305b\u3093\u3002<\/ol>\n<\/li>\n<\/ol>\n

             <\/p>\n

              \n
            1. \n
                \u30a2\u30ad\u30e5\u30e0\u30ec\u30fc\u30bf\uff1a\u8981\u7d20\u3092\u7d50\u679c\u30b3\u30f3\u30c6\u30ca\u306b\u6298\u308a\u305f\u305f\u3080\u72b6\u614b\u3092\u6301\u305f\u306a\u3044\u95a2\u6570\u3002<\/ol>\n<\/li>\n<\/ol>\n

                 <\/p>\n

                  \u30b3\u30f3\u30d0\u30a4\u30ca\u30fc\uff1a\u4e8c\u3064\u306e\u90e8\u5206\u7684\u306a\u7d50\u679c\u30b3\u30f3\u30c6\u30ca\u3092\u53d7\u3051\u5165\u308c\u3001\u305d\u308c\u3089\u3092\u30de\u30fc\u30b8\u3059\u308b\u3001\u30a2\u30ad\u30e5\u30e0\u30ec\u30fc\u30bf\u95a2\u6570\u3068\u4e92\u63db\u6027\u304c\u5fc5\u8981\u306a\u72b6\u614b\u3092\u6301\u305f\u306a\u3044\u95a2\u6570\u3002<\/ol>\n

                  stream.collect()\u30e1\u30bd\u30c3\u30c9\u306e\u4f8b<\/h2>\n

                  Stream.collect()\u30e1\u30bd\u30c3\u30c9\u306e\u3044\u304f\u3064\u304b\u306e\u4f8b\u3092\u898b\u3066\u307f\u307e\u3057\u3087\u3046\u3002<\/p>\n

                  1. \u6587\u5b57\u5217\u306e\u30ea\u30b9\u30c8\u3092\u7d50\u5408\u3059\u308b<\/h3>\n

                  \u4f8b\u3048\u3070\u3001\u65b0\u3057\u3044\u6587\u5b57\u5217\u3092\u4f5c\u308b\u305f\u3081\u306b\u6587\u5b57\u5217\u306e\u30ea\u30b9\u30c8\u3092\u9023\u7d50\u3057\u305f\u3044\u3068\u3057\u307e\u3057\u3087\u3046\u3002\u79c1\u305f\u3061\u306f\u3001Stream\u306ecollect()\u95a2\u6570\u3092\u4f7f\u7528\u3057\u3066\u3001\u53ef\u5909\u306e\u7e2e\u5c0f\u64cd\u4f5c\u3092\u884c\u3044\u3001\u30ea\u30b9\u30c8\u306e\u8981\u7d20\u3092\u9023\u7d50\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n

                  List<String> vowels = List.of(\"a\", \"e\", \"i\", \"o\", \"u\");\r\n\r\n\/\/ sequential stream - nothing to combine\r\nStringBuilder result = vowels.stream().collect(StringBuilder::new, (x, y) -> x.append(y),\r\n\t\t(a, b) -> a.append(\",\").append(b));\r\nSystem.out.println(result.toString());\r\n\r\n\/\/ parallel stream - combiner is combining partial results\r\nStringBuilder result1 = vowels.parallelStream().collect(StringBuilder::new, (x, y) -> x.append(y),\r\n\t\t(a, b) -> a.append(\",\").append(b));\r\nSystem.out.println(result1.toString());\r\n<\/code><\/pre>\n
                  \u7d50\u679c: \u51fa\u529b<\/p>\n
                  aeiou\r\na,e,i,o,u\r\n<\/code><\/pre>\n
                    \n
                  • The supplier function is returning a new StringBuilder object in every call.<\/li>\n
                  • The accumulator function is appending the list string element to the StringBuilder instance.<\/li>\n
                  • The combiner function is merging the StringBuilder instances. The instances are merged with each other with a comma between them.<\/li>\n
                  • In the first case, we have a sequential stream of elements. So they are processed one by one and there is only one instance of StringBuilder. There is no use of the combiner function. That\u2019s why the output produced is \u201caeiou\u201d.<\/li>\n
                  • In the second case, we have a parallel stream of strings. So, the elements are processed parallelly and there are multiple instances of StringBuilder that are being merged by the combiner function. Hence, the output produced is \u201ca,e,i,o,u\u201d.<\/li>\n
                  • If the stream source is ordered such as List, the collect() method maintains the order while processing. If the stream source is unordered such as Set, then the collect() method can produce different results in each invocation.<\/li>\n<\/ul>\n
                    \u6587\u5b57\u5217\u306e\u30ea\u30b9\u30c8\u3092\u9023\u7d50\u3057\u305f\u3044\u5834\u5408\u3001\u30b3\u30fc\u30c9\u30b5\u30a4\u30ba\u3092\u524a\u6e1b\u3059\u308b\u305f\u3081\u306b\u30e1\u30bd\u30c3\u30c9\u53c2\u7167\u3092\u4f7f\u7528\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n
                    String result2 = vowels.parallelStream()\r\n\t\t.collect(StringBuilder::new, StringBuilder::append, StringBuilder::append)\r\n\t\t.toString();\r\n<\/code><\/pre>\n
                    2. Collectors\u30af\u30e9\u30b9\u3092\u4f7f\u7528\u3057\u3066\u3001Stream collect()\u3092List\u306b\u96c6\u3081\u308b\u3002<\/h3>\n
                    Collectors\u30af\u30e9\u30b9\u306f\u3001Collector\u30a4\u30f3\u30bf\u30fc\u30d5\u30a7\u30fc\u30b9\u306e\u591a\u304f\u306e\u4fbf\u5229\u306a\u5b9f\u88c5\u3092\u63d0\u4f9b\u3057\u307e\u3059\u3002\u6574\u6570\u306e\u30ea\u30b9\u30c8\u304b\u3089\u5076\u6570\u306e\u307f\u3092\u9078\u629e\u3059\u308b\u4f8b\u3092\u898b\u3066\u307f\u307e\u3057\u3087\u3046\u3002Stream\u306efilter()\u306f\u4e2d\u9593\u64cd\u4f5c\u3067\u3042\u308a\u3001\u30b9\u30c8\u30ea\u30fc\u30e0\u3092\u8fd4\u3057\u307e\u3059\u3002\u3057\u305f\u304c\u3063\u3066\u3001\u3053\u306e\u30b9\u30c8\u30ea\u30fc\u30e0\u304b\u3089\u30ea\u30b9\u30c8\u3092\u4f5c\u6210\u3059\u308b\u305f\u3081\u306bcollect()\u95a2\u6570\u3092\u4f7f\u7528\u3057\u307e\u3059\u3002<\/p>\n
                    List<Integer> numbers = List.of(1, 2, 3, 4, 5, 6);\r\n\t\t\r\nList<Integer> evenNumbers = numbers.stream().filter(x -> x % 2 == 0).collect(Collectors.toList());\r\nSystem.out.println(evenNumbers);  \/\/ [2, 4, 6]\r\n<\/code><\/pre>\n
                    Collectors.toList()\u306f\u3001\u5165\u529b\u8981\u7d20\u3092\u65b0\u3057\u3044\u30ea\u30b9\u30c8\u306b\u84c4\u7a4d\u3059\u308bCollector\u306e\u5b9f\u88c5\u3092\u8fd4\u3057\u307e\u3059\u3002<\/p>\n
                    3. \u30b9\u30c8\u30ea\u30fc\u30e0\u3092collect()\u30e1\u30bd\u30c3\u30c9\u3067Set\u306b\u5909\u63db\u3059\u308b<\/h3>\n
                    \u79c1\u305f\u3061\u306f\u3001Collectors.toSet()\u3092\u4f7f\u7528\u3057\u3066\u3001\u30b9\u30c8\u30ea\u30fc\u30e0\u306e\u8981\u7d20\u3092\u65b0\u3057\u3044Set\u306b\u53ce\u96c6\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n
                    List<Integer> numbers = List.of(1, 2, 3, 4, 5, 6);\r\n\r\nSet<Integer> oddNumbers = numbers.parallelStream().filter(x -> x % 2 != 0).collect(Collectors.toSet());\r\nSystem.out.println(oddNumbers); \/\/ [1, 3, 5]\r\n<\/code><\/pre>\n
                    3. \u30b9\u30c8\u30ea\u30fc\u30e0\u306ecollect()\u30e1\u30bd\u30c3\u30c9\u3092\u4f7f\u3063\u3066Map\u306b\u5909\u63db\u3059\u308b\u3002<\/h3>\n
                    \u30b9\u30c8\u30ea\u30fc\u30e0\u306e\u8981\u7d20\u3092Map\u306b\u96c6\u7d04\u3059\u308b\u305f\u3081\u306b\u3001Collectors.toMap()\u95a2\u6570\u3092\u4f7f\u7528\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002\u3053\u306e\u30e1\u30bd\u30c3\u30c9\u306f\u3001Map\u5185\u3067\u306e\u30ad\u30fc\u3068\u5bfe\u5fdc\u3059\u308b\u5024\u306e\u30de\u30c3\u30d4\u30f3\u30b0\u306b\u5bfe\u3057\u30662\u3064\u306e\u5f15\u6570\u3092\u53d7\u3051\u5165\u308c\u307e\u3059\u3002<\/p>\n
                    List<Integer> numbers = List.of(1, 2, 3, 4, 5, 6);\r\n\r\nMap<Integer, String> mapOddNumbers = numbers.parallelStream().filter(x -> x % 2 != 0)\r\n\t\t.collect(Collectors.toMap(Function.identity(), x -> String.valueOf(x)));\r\nSystem.out.println(mapOddNumbers); \/\/ {1=1, 3=3, 5=5}\r\n<\/code><\/pre>\n
                    4. \u30b3\u30ec\u30af\u30bf\u30fc\u304c\u53c2\u52a0\u3059\u308b\uff08\uff09\u4f8b<\/h3>\n
                    \u79c1\u305f\u3061\u306f\u3001Collectors joining() \u30e1\u30bd\u30c3\u30c9\u3092\u4f7f\u7528\u3059\u308b\u3053\u3068\u3067\u3001\u5165\u529b\u30b9\u30c8\u30ea\u30fc\u30e0\u306eCharSequence\u8981\u7d20\u3092\u906d\u9047\u3057\u305f\u9806\u306b\u9023\u7d50\u3059\u308bCollector\u3092\u53d6\u5f97\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002\u3053\u308c\u3092\u4f7f\u7528\u3057\u3066\u3001\u6587\u5b57\u5217\u3001StringBuffer\u3001\u307e\u305f\u306fStringBuilder\u306e\u30b9\u30c8\u30ea\u30fc\u30e0\u3092\u9023\u7d50\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n
                    jshell> String value = Stream.of(\"a\", \"b\", \"c\").collect(Collectors.joining());\r\nvalue ==> \"abc\"\r\n\r\njshell> String valueCSV = Stream.of(\"a\", \"b\", \"c\").collect(Collectors.joining(\",\"));\r\nvalueCSV ==> \"a,b,c\"\r\n\r\njshell> String valueCSVLikeArray = Stream.of(\"a\", \"b\", \"c\").collect(Collectors.joining(\",\", \"{\", \"}\"));\r\nvalueCSVLikeArray ==> \"{a,b,c}\"\r\n\r\njshell> String valueObject = Stream.of(\"1\", new StringBuffer(\"2\"), new StringBuilder(\"3\")).collect(Collectors.joining());\r\nvalueObject ==> \"123\"\r\n<\/code><\/pre>\n
                    \u51fa\u529b:<\/p>\n
                    \"Java<\/div>\n
                    \u7d50\u8ad6<\/h2>\n
                    Java\u306eStream\u306ecollect()\u306f\u3001\u4e3b\u306b\u30b9\u30c8\u30ea\u30fc\u30e0\u306e\u8981\u7d20\u3092\u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u306b\u96c6\u3081\u308b\u305f\u3081\u306b\u4f7f\u7528\u3055\u308c\u307e\u3059\u3002\u3053\u308c\u306f\u7d42\u7aef\u64cd\u4f5c\u3067\u3059\u3002\u4e26\u5217\u30b9\u30c8\u30ea\u30fc\u30e0\u3068\u4e00\u7dd2\u306b\u4f7f\u7528\u3059\u308b\u969b\u306b\u306f\u3001\u540c\u671f\u51e6\u7406\u3092\u62c5\u5f53\u3057\u307e\u3059\u3002Collectors\u30af\u30e9\u30b9\u306f\u3001\u79c1\u305f\u3061\u3092\u52a9\u3051\u308b\u305f\u3081\u306b\u591a\u304f\u306eCollector\u5b9f\u88c5\u3092\u63d0\u4f9b\u3057\u307e\u3059\u3002<\/p>\n
                    \u30ea\u30d5\u30a1\u30ec\u30f3\u30b9<\/h2>\n
                      \n
                    • Stream collect() API Doc<\/li>\n
                    • Collector Interface<\/li>\n
                    • Collectors API Doc<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"
                      Java Stream\u306ecollect()\u306f\u3001\u30b9\u30c8\u30ea\u30fc\u30e0\u306e\u8981\u7d20\u306b\u5bfe\u3057\u3066\u53ef\u5909\u306e\u96c6\u7d04\u64cd\u4f5c\u3092\u5b9f\u884c\u3057\u307e\u3059\u3002\u3053\u306e\u64cd\u4f5c\u306f\u7d42\u7aef\u64cd\u4f5c\u3067\u3059\u3002 \u53ef\u5909\u524a\u6e1b\u64cd\u4f5c\u3068\u306f\u4f55\u3067\u3059\u304b\uff1f (Kahen saku gen s\u014dsa to wa nanides […]<\/p>\n","protected":false},"author":6,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[26,61],"class_list":["post-930","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-26","tag-61"],"yoast_head":"\nJava Stream\u306ecollect()\u30e1\u30bd\u30c3\u30c9\u306e\u4f8b - Blog - Silicon Cloud<\/title>\n<meta name=\"description\" content=\"Java Stream\u306ecollect()\u30e1\u30bd\u30c3\u30c9\u306e\u4f8b\u3092\u5206\u304b\u308a\u3084\u3059\u304f\u89e3\u8aac\u3002\u5b9f\u8df5\u7684\u306a\u4f8b\u3068\u30b3\u30fc\u30c9\u3001\u6ce8\u610f\u70b9\u3092\u542b\u3081\u3066\u521d\u5fc3\u8005\u306b\u3082\u7406\u89e3\u3067\u304d\u308b\u3088\u3046\u8aac\u660e\u3057\u307e\u3059\u3002\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.silicloud.com\/ja\/blog\/java-stream\u306ecollect\u30e1\u30bd\u30c3\u30c9\u306e\u4f8b\/\" \/>\n<meta property=\"og:locale\" content=\"ja_JP\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Java Stream\u306ecollect()\u30e1\u30bd\u30c3\u30c9\u306e\u4f8b\" \/>\n<meta property=\"og:description\" content=\"Java Stream\u306ecollect()\u30e1\u30bd\u30c3\u30c9\u306e\u4f8b\u3092\u5206\u304b\u308a\u3084\u3059\u304f\u89e3\u8aac\u3002\u5b9f\u8df5\u7684\u306a\u4f8b\u3068\u30b3\u30fc\u30c9\u3001\u6ce8\u610f\u70b9\u3092\u542b\u3081\u3066\u521d\u5fc3\u8005\u306b\u3082\u7406\u89e3\u3067\u304d\u308b\u3088\u3046\u8aac\u660e\u3057\u307e\u3059\u3002\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.silicloud.com\/ja\/blog\/java-stream\u306ecollect\u30e1\u30bd\u30c3\u30c9\u306e\u4f8b\/\" \/>\n<meta property=\"og:site_name\" content=\"Blog - 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