{"id":672593,"date":"2026-01-09T03:26:42","date_gmt":"2026-01-09T02:26:42","guid":{"rendered":"https:\/\/blog.jetbrains.com\/kotlin\/2025\/10\/evaluating-kotlin-in-real-projects\/"},"modified":"2026-01-19T06:17:12","modified_gmt":"2026-01-19T05:17:12","slug":"evaluating-kotlin-in-real-projects","status":"publish","type":"kotlin","link":"https:\/\/blog.jetbrains.com\/ja\/kotlin\/2026\/01\/evaluating-kotlin-in-real-projects\/","title":{"rendered":"\u5b9f\u969b\u306e\u30d7\u30ed\u30b8\u30a7\u30af\u30c8\u306b\u304a\u3051\u308b Kotlin \u306e\u8a55\u4fa1\u624b\u6cd5"},"content":{"rendered":"

Urs Peter<\/a>\uff08\u30b7\u30cb\u30a2\u30bd\u30d5\u30c8\u30a6\u30a7\u30a2\u30a8\u30f3\u30b8\u30cb\u30a2\u3001JetBrains \u8a8d\u5b9a Kotlin \u30c8\u30ec\u30fc\u30ca\u30fc\uff09\u306b\u3088\u308b\u30b2\u30b9\u30c8\u6295\u7a3f\u3067\u3059\u3002 Urs \u306f\u3001\u3088\u308a\u4f53\u7cfb\u7684\u306a Kotlin \u30b9\u30ad\u30eb\u306e\u69cb\u7bc9\u3092\u5e0c\u671b\u3059\u308b\u958b\u767a\u8005\u3092\u5bfe\u8c61\u3068\u3059\u308b <\/em>Kotlin Upskill Program<\/em><\/a>\uff08Kotlin \u30b9\u30ad\u30eb\u30a2\u30c3\u30d7\u30d7\u30ed\u30b0\u30e9\u30e0\uff09\u3082 Xebia Academy \u3067<\/em>\u958b\u8b1b\u3057\u3066\u3044\u307e\u3059\u3002<\/p>\n

\u3053\u306e\u8a18\u4e8b\u306f\u3001\u5b9f\u969b\u306e\u30c1\u30fc\u30e0\u3067\u3042\u308b\u958b\u767a\u8005\u306e\u597d\u5947\u5fc3\u3092\u304d\u3063\u304b\u3051\u306b\u4f1a\u793e\u5168\u4f53\u304c\u5909\u9769\u3059\u308b\u307e\u3067\u306e Kotlin \u306e\u5c0e\u5165\u7d4c\u7def\u3092\u8ffd\u3063\u305f\u300c<\/em>Java \u4e3b\u4f53\u306e\u74b0\u5883\u3067 Kotlin \u306e\u5c0e\u5165\u3092\u6210\u529f\u3055\u305b\u308b\u305f\u3081\u306e\u7a76\u6975\u30ac\u30a4\u30c9<\/em><\/strong>\u300d\u9023\u8f09\u8a18\u4e8b\u306e\u7b2c 2 \u56de\u3067\u3059\u3002<\/em><\/p>\n

\u9023\u8f09\u306e\u7b2c 1 \u56de\u3092\u8aad\u3080: Java \u958b\u767a\u8005\u5411\u3051 Kotlin \u306e\u57fa\u790e<\/a><\/p>\n

\n

\u8a55\u4fa1\u6bb5\u968e: \u30d7\u30ec\u30a4\u30b0\u30e9\u30a6\u30f3\u30c9\u3067\u306e Kotlin \u3092\u8131\u5374<\/strong><\/h2>\n

\u30c6\u30b9\u30c8\u3067 Kotlin \u306b\u6163\u308c\u305f\u3089\u3001\u3088\u308a\u672c\u683c\u7684\u306a\u8a55\u4fa1\u3092\u59cb\u3081\u307e\u3057\u3087\u3046\u3002 \u3053\u308c\u306b\u306f\u4e3b\u306b 2 \u3064\u306e\u65b9\u6cd5\u304c\u3042\u308a\u307e\u3059\u3002<\/p>\n

    \n
  1. Kotlin \u3067\u65b0\u3057\u3044\u30de\u30a4\u30af\u30ed\u30b5\u30fc\u30d3\u30b9 \/ \u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u3092\u69cb\u7bc9\u3059\u308b<\/a><\/li>\n
  2. \u65e2\u5b58\u306e Java \u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u3092\u62e1\u5f35 \/ \u5909\u63db\u3059\u308b<\/a><\/li>\n<\/ol>\n

    1. Kotlin \u3067\u65b0\u3057\u3044\u30de\u30a4\u30af\u30ed\u30b5\u30fc\u30d3\u30b9 \/ \u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u3092\u69cb\u7bc9\u3059\u308b<\/strong><\/h3>\n

    \u65b0\u898f\u306e\u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u307e\u305f\u306f\u30de\u30a4\u30af\u30ed\u30b5\u30fc\u30d3\u30b9\u3092\u4f7f\u3063\u3066\u65b0\u305f\u306b\u59cb\u3081\u308b\u3068\u3001\u65e2\u5b58\u30b3\u30fc\u30c9\u306e\u5236\u7d04\u3092\u53d7\u3051\u305a\u306b\u5b8c\u5168\u306a Kotlin \u30a8\u30af\u30b9\u30da\u30ea\u30a8\u30f3\u30b9\u3092\u63d0\u4f9b\u3067\u304d\u307e\u3059\u3002 \u3053\u306e\u65b9\u6cd5\u3067\u306f\u6700\u9ad8\u306e\u5b66\u7fd2\u30a8\u30af\u30b9\u30da\u30ea\u30a8\u30f3\u30b9\u3092\u5f97\u3089\u308c\u308b\u3053\u3068\u304c\u591a\u304f\u3001Kotlin \u306e\u5f37\u307f\u3092\u6700\u3082\u3088\u304f\u7406\u89e3\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n

    \n
    \n

    \u30d7\u30ed\u958b\u767a\u8005\u304b\u3089\u306e\u30d2\u30f3\u30c8<\/strong>: \u3053\u306e\u6bb5\u968e\u3067\u306f\u5c02\u9580\u5bb6\u304b\u3089\u306e\u652f\u63f4\u3092\u5f97\u307e\u3057\u3087\u3046\u3002 \u958b\u767a\u8005\u304c\u81ea\u5206\u306e\u80fd\u529b\u306b\u81ea\u4fe1\u3092\u6301\u3064\u306e\u306f\u7121\u7406\u304b\u3089\u306c\u3053\u3068\u3067\u3059\u304c\u3001Java \u30e9\u30a4\u30af\u306a Kotlin \u3084 Kotlin \u30d9\u30fc\u30b9\u306e\u30e9\u30a4\u30d6\u30e9\u30ea\u306e\u4e0d\u4f7f\u7528\u3068\u3044\u3063\u305f\u30df\u30b9\u3092\u65e9\u3044\u6bb5\u968e\u3067\u56de\u907f\u3059\u308b\u3053\u3068\u3067\u3001\u6570\u304b\u6708\u5206\u306e\u6280\u8853\u7684\u8ca0\u50b5\u3092\u306a\u304f\u3059\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n<\/div>\n

    \n
    \"\"<\/figure>\n<\/div>\n<\/div>\n

    \u305d\u3046\u3059\u308b\u3053\u3068\u3067\u3001\u4ee5\u4e0b\u306e\u3088\u3046\u306a Java \u7d4c\u9a13\u8005\u304c Kotlin \u3092\u4f7f\u7528\u3059\u308b\u969b\u306e\u3088\u304f\u3042\u308b\u843d\u3068\u3057\u7a74\u3092\u56de\u907f\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n

    \u843d\u3068\u3057\u7a74: \u81ea\u5206\u304c Java \u3067\u4f7f\u7528\u3057\u3066\u3044\u308b\u30d5\u30ec\u30fc\u30e0\u30ef\u30fc\u30af\u3068\u306f\u5225\u306e\u30d5\u30ec\u30fc\u30e0\u30ef\u30fc\u30af\u3092\u9078\u629e\u3059\u308b\u3002<\/em><\/p>\n

    \u30d2\u30f3\u30c8: \u65e2\u5b58\u306e\u30d5\u30ec\u30fc\u30e0\u30ef\u30fc\u30af\u3092\u305d\u306e\u307e\u307e\u4f7f\u7528\u3057\u307e\u3057\u3087\u3046<\/strong>\u3002<\/p>\n

    Java \u3067 Spring Boot \u3092\u4f7f\u7528\u3057\u3066\u3044\u305f\u306e\u306a\u3089\u3001Kotlin \u3067\u3082\u305d\u308c\u3092\u4f7f\u7528\u3057\u307e\u3057\u3087\u3046\u3002 Spring Boot \u306f\u6700\u9ad8\u6c34\u6e96\u306e Kotlin \u306e\u30b5\u30dd\u30fc\u30c8\u3092\u63d0\u4f9b\u3057\u3066\u3044\u308b\u305f\u3081\u3001\u4ed6\u306e\u30d5\u30ec\u30fc\u30e0\u30ef\u30fc\u30af\u3092\u4f7f\u7528\u3059\u308b\u30e1\u30ea\u30c3\u30c8\u306f\u7279\u306b\u3042\u308a\u307e\u305b\u3093\u3002 \u3055\u3089\u306b\u3001\u65b0\u3057\u3044\u8a00\u8a9e\u3082\u65b0\u3057\u3044\u30d5\u30ec\u30fc\u30e0\u30ef\u30fc\u30af\u3082\u5b66\u3070\u3056\u308b\u3092\u5f97\u306a\u304f\u306a\u308b\u305f\u3081\u3001\u4e8b\u304c\u8907\u96d1\u5316\u3059\u308b\u3060\u3051\u3067\u4f55\u306e\u30e1\u30ea\u30c3\u30c8\u3082\u3042\u308a\u307e\u305b\u3093\u3002<\/p>\n

    \u91cd\u8981\u4e8b\u9805<\/strong>: Spring \u306f\u62e1\u5f35\u5bfe\u8c61\u306e\u30af\u30e9\u30b9\u306b open \u3092\u660e\u793a\u7684\u306b\u6307\u5b9a\u3059\u308b\u3053\u3068\u3092\u8981\u6c42\u3059\u308b Kotlin \u306e\u300c\u610f\u56f3\u7684\u306a\u7d99\u627f\u300d\u306e\u539f\u5247\u306b\u5e72\u6e09\u3057\u307e\u3059\u3002<\/p>\n

    open \u30ad\u30fc\u30ef\u30fc\u30c9\u3092\u3059\u3079\u3066\u306e Spring \u95a2\u9023\u30af\u30e9\u30b9\uff08@Configuration<\/code> \u306a\u3069\uff09\u306b\u8ffd\u52a0\u3057\u306a\u3044\u3088\u3046\u306b\u3059\u308b\u306b\u306f\u3001https:\/\/kotlinlang.org\/docs\/all-open-plugin.html#spring-support<\/a> \u306b\u3042\u308b\u30d3\u30eb\u30c9\u30d7\u30e9\u30b0\u30a4\u30f3\u3092\u4f7f\u7528\u3067\u304d\u307e\u3059\u3002 \u6709\u540d\u306a\u30aa\u30f3\u30e9\u30a4\u30f3 Spring initializr \u30c4\u30fc\u30eb<\/a>\u3067 Spring \u30d7\u30ed\u30b8\u30a7\u30af\u30c8\u3092\u4f5c\u6210\u3057\u305f\u5834\u5408\u306f\u3001\u3053\u306e\u30d3\u30eb\u30c9\u30d7\u30e9\u30b0\u30a4\u30f3\u306f\u3042\u3089\u304b\u3058\u3081\u69cb\u6210\u3055\u308c\u3066\u3044\u307e\u3059\u3002<\/p>\n

    \u843d\u3068\u3057\u7a74: Java \u30e9\u30a4\u30af\u306a Kotlin \u3092\u66f8\u304f\u3001Kotlin \u306e\u6a19\u6e96\u30e9\u30a4\u30d6\u30e9\u30ea\u3067\u306f\u306a\u304f\u4e00\u822c\u7684\u306a Java API \u3092\u4f7f\u7528\u3059\u308b:<\/em><\/p>\n

    \u3059\u3079\u3066\u306e\u843d\u3068\u3057\u7a74\u3092\u5217\u6319\u3059\u308b\u3068\u975e\u5e38\u306b\u9577\u304f\u306a\u3063\u3066\u3057\u307e\u3046\u306e\u3067\u3001\u6700\u3082\u3088\u304f\u3042\u308b\u3082\u306e\u306b\u7d5e\u308a\u307e\u3057\u3087\u3046\u3002<\/p>\n

    \u843d\u3068\u3057\u7a74 1: Kotlin \u306e\u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u3067\u306f\u306a\u304f Java \u306e\u30b9\u30c8\u30ea\u30fc\u30e0\u3092\u4f7f\u7528\u3059\u308b<\/em><\/h4>\n

    \u30d2\u30f3\u30c8: \u5e38\u306b Kotlin \u306e\u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u3092\u4f7f\u7528\u3057\u307e\u3057\u3087\u3046\u3002<\/strong><\/p>\n

    Kotlin \u306e\u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u306f Java \u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u3068\u5b8c\u5168\u306b\u76f8\u4e92\u904b\u7528\u53ef\u80fd\u3067\u3059\u304c\u3001Java \u30b9\u30c8\u30ea\u30fc\u30e0\u306e\u5fc5\u8981\u6027\u3092\u306a\u304f\u3059\u7c21\u6f54\u3067\u6a5f\u80fd\u8c4a\u5bcc\u306a\u9ad8\u968e\u95a2\u6570\u304c\u5099\u308f\u3063\u3066\u3044\u307e\u3059\u3002<\/p>\n

    \u4ee5\u4e0b\u306f\u53ce\u76ca\u5225\uff08\u5358\u4fa1 x \u8ca9\u58f2\u6570\uff09\u306b\u4e0a\u4f4d 3 \u3064\u306e\u5546\u54c1\u3092\u9078\u629e\u3057\u3001\u5546\u54c1\u30ab\u30c6\u30b4\u30ea\u3067\u30b0\u30eb\u30fc\u30d7\u5316\u3059\u308b\u3053\u3068\u3092\u76ee\u7684\u3068\u3057\u305f\u4f8b\u3067\u3059\u3002<\/p>\n

    Java<\/strong><\/p>\n

    record Product(String name, String category, double price, int sold){}\n\nList products = List.of(\n           new Product(\"Lollipop\", \"sweets\", 1.2, 321),\n           new Product(\"Broccoli\", \"vegetable\", 1.8, 5);\n\nMap<String, List> top3RevenueByCategory =\n       products.stream()\n          .collect(Collectors.groupingBy(\n                Product::category,\n                Collectors.collectingAndThen(\n                    Collectors.toList(),\n                    list -> list.stream()\n                              .sorted(Comparator.comparingDouble(\n                                  (Product p) -> p.price() * p.sold())\n                                   .reversed())\n                                   .limit(3)\n                                   .toList()\n                       \t\t)\n          )\n);<\/pre>\n
    Kotlin<\/strong><\/p>\n
    val top3RevenueByCategory: Map<String, List> =\n   products.groupBy { it.category }\n       .mapValues { (_, list) ->\n           list.sortedByDescending { it.price * it.sold }.take(3)\n       }<\/pre>\n
    Kotlin \u306e Java \u3068\u306e\u76f8\u4e92\u904b\u7528\u6027\u306b\u3088\u308a\u3001Java \u306e\u30af\u30e9\u30b9\u3068\u30ec\u30b3\u30fc\u30c9\u3092\u30cd\u30a4\u30c6\u30a3\u30d6\u306a Kotlin \u3067\u3042\u308b\u304b\u306e\u3088\u3046\u306b\u6271\u3046\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002\u305f\u3060\u3057\u3001Kotlin \u306e\uff08data\uff09\u30af\u30e9\u30b9\u3092\u4ee3\u308f\u308a\u306b\u4f7f\u7528\u3059\u308b\u3053\u3068\u3082\u53ef\u80fd\u3067\u3059\u3002<\/p>\n
    \u843d\u3068\u3057\u7a74 2: Java \u306e Optional \u3092\u4f7f\u7528\u3057\u7d9a\u3051\u308b<\/em><\/h4>\n
    \u30d2\u30f3\u30c8: null \u8a31\u5bb9\u578b\u3092\u53d6\u308a\u5165\u308c\u307e\u3057\u3087\u3046<\/strong>\u3002<\/p>\n
    Java \u958b\u767a\u8005\u304c Kotlin \u306b\u79fb\u884c\u3059\u308b\u4e3b\u306a\u7406\u7531\u306e 1 \u3064\u306b\u306f\u3001Kotlin \u304c null \u8a31\u5bb9\u6027\u3092\u7d44\u307f\u8fbc\u307f\u3067\u30b5\u30dd\u30fc\u30c8\u3057\u3066\u3044\u308b\u305f\u3081\u3001NullPointerExceptions \u3092\u4f7f\u7528\u3059\u308b\u5fc5\u8981\u304c\u306a\u304f\u306a\u308b\u3053\u3068\u304c\u3042\u308a\u307e\u3059\u3002 \u305d\u306e\u305f\u3081\u3001Optional \u3067\u306f\u306a\u304f\u3001null \u8a31\u5bb9\u578b\u3092\u4f7f\u7528\u3059\u308b\u3088\u3046\u306b\u3057\u307e\u3057\u3087\u3046\u3002 \u307e\u3060\u30a4\u30f3\u30bf\u30fc\u30d5\u30a7\u30fc\u30b9\u306b Optional \u3092\u4f7f\u7528\u3057\u3066\u3044\u307e\u3059\u304b\uff1f \u4ee5\u4e0b\u306e\u3088\u3046\u306b\u3059\u308b\u3068\u3001Optional \u3092\u7c21\u5358\u306b null \u8a31\u5bb9\u578b\u306b\u5909\u63db\u3057\u3066\u524a\u9664\u3067\u304d\u307e\u3059\u3002<\/p>\n
    Kotlin<\/strong><\/p>\n
    \/\/Let\u2019s assume this repository is hard to change, because it\u2019s a library you depend on\nclass OrderRepository {\n      \/\/it returns Optional, but we want nullable types\n      fun getOrderBy(id: Long): Optional = \u2026\n}\n\n\/\/Simply add an extension method and apply the orElse(null) trick\nfun OrderRepository.getOrderByOrNull(id: Long): Order? = \n                                    getOrderBy(id).orElse(null)\n\n\/\/Now enjoy the safety and ease of use of nullable types:\n\n\/\/Past:\n val g = repository.getOrderBy(12).flatMap { product ->\n     product.goody.map { it.name }\n}.orElse(\"No goody found\")\n\n\/\/Future:\n val g = repository.getOrderByOrNull(12)?.goody?.name ?: \"No goody found\"<\/pre>\n
    \u843d\u3068\u3057\u7a74 3: \u9759\u7684\u30e9\u30c3\u30d1\u30fc\u3092\u4f7f\u7528\u3057\u7d9a\u3051\u308b<\/em><\/h4>\n
    \u30d2\u30f3\u30c8: \u62e1\u5f35\u30e1\u30bd\u30c3\u30c9\u3092\u53d6\u308a\u5165\u308c\u307e\u3057\u3087\u3046<\/strong>\u3002<\/p>\n
    \u62e1\u5f35\u30e1\u30bd\u30c3\u30c9\u306b\u306f\u4ee5\u4e0b\u306e\u3088\u3046\u306a\u591a\u304f\u306e\u30e1\u30ea\u30c3\u30c8\u304c\u3042\u308a\u307e\u3059\u3002<\/p>\n