{"record":{"id":"7db55e5f8cba789f","repo":"apache/flink","slug":"could-not-instantiate-type-due-to-an-unspecif","errorCode":null,"errorMessage":"Could not instantiate type '{}' due to an unspecified exception: {}","messagePattern":"Could not instantiate type '(.+?)' due to an unspecified exception: (.+?)","errorType":"exception","errorClass":"RuntimeException","httpStatus":null,"severity":"error","filePath":"flink-core/src/main/java/org/apache/flink/util/InstantiationUtil.java","lineNumber":317,"sourceCode":"     * @return An instance of the given class.\n     * @throws RuntimeException Thrown, if the class could not be instantiated. The exception\n     *     contains a detailed message about the reason why the instantiation failed.\n     */\n    public static <T> T instantiate(Class<T> clazz) {\n        if (clazz == null) {\n            throw new NullPointerException();\n        }\n\n        // try to instantiate the class\n        try {\n            return clazz.newInstance();\n        } catch (InstantiationException | IllegalAccessException iex) {\n            // check for the common problem causes\n            checkForInstantiation(clazz);\n\n            // here we are, if non of the common causes was the problem. then the error was\n            // most likely an exception in the constructor or field initialization\n            throw new RuntimeException(\n                    \"Could not instantiate type '\"\n                            + clazz.getName()\n                            + \"' due to an unspecified exception: \"\n                            + iex.getMessage(),\n                    iex);\n        } catch (Throwable t) {\n            String message = t.getMessage();\n            throw new RuntimeException(\n                    \"Could not instantiate type '\"\n                            + clazz.getName()\n                            + \"' Most likely the constructor (or a member variable initialization) threw an exception\"\n                            + (message == null ? \".\" : \": \" + message),\n                    t);\n        }\n    }\n\n    /**\n     * Checks, whether the given class has a public nullary constructor.","sourceCodeStart":299,"sourceCodeEnd":335,"githubUrl":"https://github.com/apache/flink/blob/2f3c205e9266cb30240eb7f4fdab15cad629a70f/flink-core/src/main/java/org/apache/flink/util/InstantiationUtil.java#L299-L335","documentation":"In InstantiationUtil.instantiate(Class), clazz.newInstance() throwing InstantiationException or IllegalAccessException first triggers checkForInstantiation(clazz) to report common causes; if none apply, the method throws RuntimeException('Could not instantiate type X due to an unspecified exception: msg'). 'Unspecified' here usually means the no-arg constructor is not accessible to the caller — e.g. package-private or protected constructor with a security/module restriction.","triggerScenarios":"A class whose nullary constructor exists but is not public (IllegalAccessException), or instantiation blocked by a Java module does-not-open rule (IllegalAccessException/InaccessibleObjectException paths) — cases that pass the structural checks in checkForInstantiationError but still refuse newInstance.","commonSituations":"Third-party classes with non-public constructors; JPMS strong encapsulation on JDK 17+ refusing reflective access to unnamed-module classes; security manager remnants.","solutions":["Give the class a public no-argument constructor (or provide a Factory/Builder the framework can use instead)","On JDK 17+, add the required --add-opens java.base/java.lang=ALL-UNNAMED style JVM args if reflective instantiation of JDK classes is intended","If the class legitimately cannot have a public constructor, instantiate it yourself and pass the instance instead of the Class"],"exampleFix":"// before\nclass MyUdf { MyUdf() {} } // package-private ctor -> IllegalAccessException path\n// after\npublic class MyUdf { public MyUdf() {} }","handlingStrategy":"validation","validationCode":"if (clazz.getConstructor() == null || !Modifier.isPublic(clazz.getConstructor().getModifiers())) {\n    // fix the constructor before letting Flink instantiate\n}","typeGuard":null,"tryCatchPattern":"try { T t = InstantiationUtil.instantiate(clazz); } catch (RuntimeException e) { /* inspect getCause(): accessibility vs constructor failure */ }","preventionTips":["Always provide a public no-arg constructor on reflectively instantiated classes","On JDK 17+, add required --add-opens flags for reflective access"],"tags":["reflection","instantiation","accessibility","jpms"],"backgroundTag":null,"analyzedSha":"2f3c205e9266cb30240eb7f4fdab15cad629a70f","analyzedAt":"2026-08-14T08:48:24.518Z","schemaVersion":2},"datasetVersion":"2026-08-14T10:17:34.591Z"}