{"record":{"id":"ab845eb34983eae0","repo":"java-native-access/jna","slug":"exception-thrown-while-instantiating-an-instance-of-type","errorCode":null,"errorMessage":"Exception thrown while instantiating an instance of \" + type","messagePattern":"Exception thrown while instantiating an instance of \" \\+ type","errorType":"exception","errorClass":"IllegalArgumentException","httpStatus":null,"severity":"error","filePath":"src/com/sun/jna/Structure.java","lineNumber":1960,"sourceCode":"            if (ctor != null) {\n                return ctor.newInstance(init);\n            }\n            // Not defined, fall back to the default\n        }\n        catch(SecurityException e) {\n            // Might as well try the fallback\n        }\n        catch(InstantiationException e) {\n            String msg = \"Can't instantiate \" + type;\n            throw new IllegalArgumentException(msg, e);\n        }\n        catch(IllegalAccessException e) {\n            String msg = \"Instantiation of \" + type + \" (Pointer) not allowed, is it public?\";\n            throw new IllegalArgumentException(msg, e);\n        }\n        catch(InvocationTargetException e) {\n            String msg = \"Exception thrown while instantiating an instance of \" + type;\n            throw new IllegalArgumentException(msg, e);\n        }\n        T s = newInstance(type);\n        if (init != PLACEHOLDER_MEMORY) {\n            s.useMemory(init);\n        }\n        return s;\n    }\n\n    /**\n     * Create a new Structure instance of the given type\n     * @param type desired Structure type\n     * @return the new instance\n     * @throws IllegalArgumentException if the instantiation fails\n     */\n    public static <T extends Structure> T newInstance(Class<T> type) throws IllegalArgumentException {\n        T s = Klass.newInstance(type);\n        if (s instanceof ByValue) {\n            s.allocateMemory();","sourceCodeStart":1942,"sourceCodeEnd":1978,"githubUrl":"https://github.com/java-native-access/jna/blob/d036ad9781adad4b66693e8fa7098e4ac665e0a3/src/com/sun/jna/Structure.java#L1942-L1978","documentation":"When Structure.newInstance(Class, Pointer) invokes the structure's (Pointer) constructor and that constructor itself throws an exception, JNA wraps the InvocationTargetException as IllegalArgumentException with \"Exception thrown while instantiating an instance of <type>\". The real error is the cause inside the user's constructor, not JNA itself.","triggerScenarios":"A Structure's (Pointer) constructor (or super-constructor / instance initializers it runs, e.g. read(), field init, validate()) throws any RuntimeException or Error; triggered via Structure.newInstance(type, pointer), nested by-value field initialization, or JNA materializing a native return value.","commonSituations":"Constructor calls read() and a field-order validation fails; constructor dereferences a null Pointer; constructor has assertions or validation that fail on PLACEHOLDER_MEMORY instances JNA creates for size calculation; exceptions from field initializers of the subclass.","solutions":["Inspect getCause() / the 'Caused by' of the IllegalArgumentException to find the exception thrown inside the constructor.","Guard the (Pointer) constructor against placeholder instances used for size calculation (e.g. avoid read() or validation on null/zero pointers).","Move expensive validation out of the constructor into a separate method invoked after JNA fully initializes the struct.","Fix field initializers that can throw (null dereferences, array sizing, NativeMapped defaults) so construction succeeds."],"exampleFix":"// before\npublic MyStruct(Pointer p) { super(p); if (p == null) throw new IllegalStateException(\"null\"); read(); }\n// after\npublic MyStruct(Pointer p) { super(p); if (p != null) read(); }","handlingStrategy":"try-catch","validationCode":null,"typeGuard":null,"tryCatchPattern":"try {\n    MyStruct s = Structure.newInstance(MyStruct.class, ptr);\n} catch (IllegalArgumentException e) {\n    if (e.getCause() instanceof InvocationTargetException) {\n        Throwable real = e.getCause().getCause();\n        throw new IllegalStateException(\"Constructor of MyStruct threw: \" + real, real);\n    }\n    throw e;\n}","preventionTips":["Never throw from Structure constructors - keep them trivial (super(p); read()) and validate later","Avoid read()-time validation inside constructors: JNA creates placeholder instances during size calculation that may not satisfy assumptions","Null-check the Pointer argument rather than throwing when JNA probes the class","Always unwrap InvocationTargetException (via getCause) to see the actual constructor exception"],"tags":["jna","structure","constructor","invocation-target","reflection"],"backgroundTag":"invalid-constructor-argument","analyzedSha":"d036ad9781adad4b66693e8fa7098e4ac665e0a3","analyzedAt":"2026-09-12T06:50:59.239Z","contentChangedAt":"2026-09-12T06:50:59.239Z","schemaVersion":2},"datasetVersion":"2026-09-14T05:17:10.506Z"}