{"record":{"id":"ee931a9f83eef9b2","repo":"java-native-access/jna","slug":"exception-reading-field-f-getname-in-getclass","errorCode":null,"errorMessage":"Exception reading field '\" + f.getName() + \"' in \" + getClass()","messagePattern":"Exception reading field '\" \\+ f\\.getName\\(\\) \\+ \"' in \" \\+ getClass\\(\\)","errorType":"exception","errorClass":"Error","httpStatus":null,"severity":"error","filePath":"src/com/sun/jna/Structure.java","lineNumber":1492,"sourceCode":"    }\n\n    /**\n     * Initialize any null-valued fields that should have a non-null default\n     * value.\n     */\n    @SuppressWarnings(\"UseSpecificCatch\")\n    private void initializeFields() {\n        // Get the full field list, don't care about sorting\n        List<Field> flist = getFieldList();\n        for (Field f : flist) {\n            try {\n                Object o = f.get(this);\n                if (o == null) {\n                    initializeField(f, f.getType());\n                }\n            }\n            catch (Exception e) {\n                throw new Error(\"Exception reading field '\" + f.getName() + \"' in \" + getClass(), e);\n            }\n        }\n    }\n\n    private Object initializeField(Field field, Class<?> type) {\n        Object value = null;\n        if (Structure.class.isAssignableFrom(type)\n            && !(ByReference.class.isAssignableFrom(type))) {\n            try {\n                value = newInstance((Class<? extends Structure>) type, PLACEHOLDER_MEMORY);\n                setFieldValue(field, value);\n            }\n            catch(IllegalArgumentException e) {\n                String msg = \"Can't determine size of nested structure\";\n                throw new IllegalArgumentException(msg, e);\n            }\n        }\n        else if (NativeMapped.class.isAssignableFrom(type)) {","sourceCodeStart":1474,"sourceCodeEnd":1510,"githubUrl":"https://github.com/java-native-access/jna/blob/d036ad9781adad4b66693e8fa7098e4ac665e0a3/src/com/sun/jna/Structure.java#L1474-L1510","documentation":"While initializing/pre-reading fields before a native read, reflective access f.get(this) threw. JNA wraps any such exception in java.lang.Error naming the field and Structure class, since it indicates reflective access failure rather than an expected condition.","triggerScenarios":"Field.get(this) fails during ensureInitialized/initializeFields — e.g. IllegalAccessException on non-public fields on restricted VMs, or exceptions thrown from field initializers/constructors of field objects (including Structure subclass constructors that themselves fail).","commonSituations":"Structures with private fields under strict access control; field objects whose constructors throw (recursive structure initialization, OOM); J2ME/embedded VMs lacking access override support.","solutions":["Make the failing field public and ensure its type has an accessible no-arg constructor","Fix exceptions thrown in the field's initializer or its class's constructor (check the cause chain)","Ensure initializeFields runs only when fields are writable; avoid SecurityManager restrictions blocking reflection","If a custom TypeMapper's fromNative path throws during initialization, fix that converter"],"exampleFix":"// before\nclass S extends Structure {\n    private X x = new X(); // X ctor throws or field inaccessible\n}\n// after\nclass S extends Structure {\n    public X x; // X has a safe no-arg constructor\n}","handlingStrategy":"try-catch","validationCode":"for (Field f : S.class.getFields()) {\n    try { f.setAccessible(true); } catch (SecurityException e) { throw new IllegalStateException(\"Cannot access \" + f, e); }\n}","typeGuard":null,"tryCatchPattern":"try {\n    s.read();\n} catch (Error e) {\n    if (e.getMessage() != null && e.getMessage().startsWith(\"Exception reading field\")) {\n        Throwable cause = e.getCause();\n        // fix reflective access or the field initializer that threw\n        throw new IllegalStateException(\"Fix field access/initializer: \" + e.getMessage(), cause);\n    }\n    throw e;\n}","preventionTips":["Keep structure fields public with cheap, safe initializers","Avoid constructors in field types that can throw (e.g., recursive structure init)","Ensure no SecurityManager blocks reflective field access","Test read()/write() round-trips in CI to catch access problems early"],"tags":["jna","structure","reflection","field-access"],"backgroundTag":"internal-invariant-violation","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"}