{"id":765,"date":"2025-07-17T12:22:58","date_gmt":"2025-07-17T12:22:58","guid":{"rendered":"https:\/\/boochlin.com\/?p=765"},"modified":"2025-08-27T23:17:42","modified_gmt":"2025-08-27T23:17:42","slug":"difference-between-constructors-and-init-in-kotlin","status":"publish","type":"post","link":"https:\/\/boochlin.com\/?p=765","title":{"rendered":"Difference between constructors and init in kotlin"},"content":{"rendered":"

\u539f\u6587<\/a><\/p>\n

\u8ab0\u8ca0\u8cac\u300c\u5b9a\u7fa9\u300d\uff1f\u8ab0\u8ca0\u8cac\u300c\u57f7\u884c\u300d\uff1f<\/h2>\n

\u5728 Kotlin<\/strong> \u4e2d\uff0cObject \u5275\u5efa\u662f\u500b\u6709\u9806\u5e8f\u7684\u904e\u7a0b\u3002constructor \u548c init block \u662f\u95dc\u9375\u6210\u54e1\uff0c\u5404\u81ea\u6709\u660e\u78ba\u8077\u8cac\u3002\u641e\u4e0d\u6e05\u9019\u9ede\uff0c\u53ef\u80fd\u5c0e\u81f4\u521d\u59cb\u5316\u9806\u5e8f\u932f\u8aa4\u6216 Runtime Issues\u3002<\/p>\n

\u57f7\u884c\u9806\u5e8f\uff1a<\/strong><\/h3>\n
    \n
  1. Primary Constructor<\/strong><\/li>\n
  2. Property Initializers<\/strong><\/li>\n
  3. init blocks<\/strong> (\u6309\u5ba3\u544a\u9806\u5e8f)<\/li>\n
  4. Secondary Constructor<\/strong> (\u6b21\u8981\u5efa\u69cb\u51fd\u5f0f) \u7684\u4e3b\u9ad4 (\u5982\u679c\u6709\uff0c\u4e14\u5728\u547c\u53eb Primary Constructor \u4e4b\u5f8c)<\/li>\n<\/ol>\n

    \u7c21\u55ae\u4f86\u8aaa\uff1aconstructor \u6c7a\u5b9a\u53c3\u6578\uff0cProperty \u63a5\u6536\u4e26\u521d\u59cb\u5316\uff0c\u7136\u5f8c init block \u624d\u6839\u64da\u9019\u4e9b\u53bb\u57f7\u884c\u908f\u8f2f\u3002<\/p>\n

    \n

    \u8077\u8cac\u5340\u5206<\/h2>\n
      \n
    1. constructor\uff1aObject \u7684\u300c\u521d\u59cb\u85cd\u5716\u300d\n
        \n
      • \u8077\u8cac\uff1a<\/strong> \u5b9a\u7fa9\u4e26\u63a5\u6536\u5275\u5efa Class Instance \u6240\u9700\u7684\u521d\u59cb Parameters<\/strong>\u3002<\/li>\n
      • \u985e\u578b\uff1a<\/strong>\n
          \n
        • Primary Constructor\uff1a<\/strong> \u6700\u5e38\u898b\uff0c\u76f4\u63a5\u5728 Class Header \u4e2d\u5b9a\u7fa9\uff0c\u53ef\u5c07 Parameters \u5ba3\u544a\u70ba Properties<\/strong>\u3002<\/li>\n
        • Secondary Constructor\uff1a<\/strong> \u63d0\u4f9b\u591a\u7a2e\u5275\u5efa\u65b9\u5f0f\uff0c\u4f46\u5fc5\u9808\u547c\u53eb Primary Constructor<\/strong>\u3002<\/li>\n<\/ul>\n<\/li>\n
        • \u57f7\u884c\u6642\u6a5f\uff1a<\/strong> \u5728 init blocks \u548c Property Initializers \u4e4b\u524d<\/strong>\u57f7\u884c\u3002<\/li>\n<\/ul>\n<\/li>\n
        • init block\uff1aObject \u7684\u300c\u7acb\u5373\u8a2d\u5b9a\u8207\u9a57\u8b49\u300d\n
            \n
          • \u8077\u8cac\uff1a<\/strong> \u5728 Primary Constructor \u5b8c\u6210\u5f8c\uff0c\u7acb\u5373\u57f7\u884c<\/strong>\u8207 Object \u72c0\u614b\u76f8\u95dc\u7684\u521d\u59cb\u5316 Logic<\/strong>\u3002\u5b83\u4e0d\u63a5\u6536 Parameters\uff0c\u53ea\u5229\u7528\u5df2\u6536\u5230\u7684 Parameters \u6216 Properties \u9032\u884c\u984d\u5916\u8a2d\u5b9a\u3001Validation \u6216\u8907\u96dc\u64cd\u4f5c\u3002<\/li>\n
          • \u57f7\u884c\u6642\u6a5f\uff1a<\/strong> \u7dca\u96a8 Primary Constructor \u548c\u6240\u6709 Property Initializers \u4e4b\u5f8c\u81ea\u52d5\u57f7\u884c\u3002\u53ef\u6709\u591a\u500b init blocks\uff0c\u4f9d\u5e8f\u57f7\u884c\u3002<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n
            \n

            \u6848\u4f8b\uff1a\u7528\u6236\u8a2d\u5b9a\u6a94\u7684\u521d\u59cb\u5316<\/h2>\n

            Kotlin<\/p>\n

            class UserProfile(val userId: String, email: String) { \/\/ Primary Constructor\n\u00a0 \u00a0 val emailAddress: String = email \/\/ Property Initializer\n\n\u00a0 \u00a0 init { \/\/ Init Block 1: Validation\n\u00a0 \u00a0 \u00a0 \u00a0 println(\"Init Block 1: Validating user data.\")\n\u00a0 \u00a0 \u00a0 \u00a0 require(userId.isNotBlank()) { \"User ID cannot be blank.\" }\n\u00a0 \u00a0 }\n\n\u00a0 \u00a0 init { \/\/ Init Block 2: Further setup\n\u00a0 \u00a0 \u00a0 \u00a0 println(\"Init Block 2: User profile setup complete for $userId.\")\n\u00a0 \u00a0 }\n\n\u00a0 \u00a0 constructor(userId: String) : this(userId, \"default@example.com\") { \/\/ Secondary Constructor\n\u00a0 \u00a0 \u00a0 \u00a0 println(\"Secondary Constructor: User created with default email.\")\n\u00a0 \u00a0 }\n}\n\nfun main() {\n\u00a0 \u00a0 val userA = UserProfile(\"john.doe\", \"john.doe@example.com\")\n\u00a0 \u00a0 \/\/ Output sequence:\n\u00a0 \u00a0 \/\/ Init Block 1: Validating user data.\n\u00a0 \u00a0 \/\/ Init Block 2: User profile setup complete for john.doe.\n\n\u00a0 \u00a0 println(\"---\")\n\n\u00a0 \u00a0 val userB = UserProfile(\"jane.doe\") \/\/ Calls Secondary Constructor\n\u00a0 \u00a0 \/\/ Output sequence:\n\u00a0 \u00a0 \/\/ Init Block 1: Validating user data.\n\u00a0 \u00a0 \/\/ Init Block 2: User profile setup complete for jane.doe.\n\u00a0 \u00a0 \/\/ Secondary Constructor: User created with default email.\n}\n<\/pre>\n","protected":false},"excerpt":{"rendered":"
            \u539f\u6587 \u8ab0\u8ca0\u8cac\u300c\u5b9a\u7fa9\u300d\uff1f\u8ab0\u8ca0\u8cac\u300c\u57f7\u884c\u300d\uff1f \u5728 Kotlin \u4e2d\uff0cObject \u5275\u5efa\u662f\u500b\u6709\u9806\u5e8f\u7684\u904e\u7a0b\u3002constructor \u548c init block \u662f\u95dc\u9375\u6210\u54e1\uff0c\u5404\u81ea\u6709\u660e\u78ba\u8077\u8cac\u3002\u641e\u4e0d\u6e05\u9019\u9ede\uff0c\u53ef\u80fd\u5c0e\u81f4\u521d\u59cb…<\/p>\n","protected":false},"author":1,"featured_media":879,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[81],"tags":[],"_links":{"self":[{"href":"https:\/\/boochlin.com\/index.php?rest_route=\/wp\/v2\/posts\/765"}],"collection":[{"href":"https:\/\/boochlin.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/boochlin.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/boochlin.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/boochlin.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=765"}],"version-history":[{"count":4,"href":"https:\/\/boochlin.com\/index.php?rest_route=\/wp\/v2\/posts\/765\/revisions"}],"predecessor-version":[{"id":878,"href":"https:\/\/boochlin.com\/index.php?rest_route=\/wp\/v2\/posts\/765\/revisions\/878"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/boochlin.com\/index.php?rest_route=\/wp\/v2\/media\/879"}],"wp:attachment":[{"href":"https:\/\/boochlin.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=765"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/boochlin.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=765"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/boochlin.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=765"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}