{"record":{"id":"76b2aa180019e07a","repo":"Blankj/AndroidUtilCode","slug":"u-can-t-instantiate-me-76b2aa","errorCode":null,"errorMessage":"u can't instantiate me...","messagePattern":"u can't instantiate me\\.\\.\\.","errorType":"exception","errorClass":"UnsupportedOperationException","httpStatus":null,"severity":"info","filePath":"lib/utilcode/src/main/java/com/blankj/utilcode/util/FileIOUtils.java","lineNumber":41,"sourceCode":"import java.nio.MappedByteBuffer;\nimport java.nio.channels.FileChannel;\nimport java.util.ArrayList;\nimport java.util.List;\n\n/**\n * <pre>\n *     author: Blankj\n *     blog  : http://blankj.com\n *     time  : 2017/06/22\n *     desc  : utils about file io\n * </pre>\n */\npublic final class FileIOUtils {\n\n    private static int sBufferSize = 524288;\n\n    private FileIOUtils() {\n        throw new UnsupportedOperationException(\"u can't instantiate me...\");\n    }\n\n    ///////////////////////////////////////////////////////////////////////////\n    // writeFileFromIS without progress\n    ///////////////////////////////////////////////////////////////////////////\n\n    /**\n     * Write file from input stream.\n     *\n     * @param filePath The path of file.\n     * @param is       The input stream.\n     * @return {@code true}: success<br>{@code false}: fail\n     */\n    public static boolean writeFileFromIS(final String filePath, final InputStream is) {\n        return writeFileFromIS(UtilsBridge.getFileByPath(filePath), is, false, null);\n    }\n\n    /**","sourceCodeStart":23,"sourceCodeEnd":59,"githubUrl":"https://github.com/Blankj/AndroidUtilCode/blob/7b4caf9e5440046b3fefb63b6b6e2ead7ebaf809/lib/utilcode/src/main/java/com/blankj/utilcode/util/FileIOUtils.java#L23-L59","documentation":"FileIOUtils is a final utility class whose private constructor throws UnsupportedOperationException(\"u can't instantiate me...\"). All file-I/O helpers (writeFileFromIS, writeFileFromBytes, readFile2Bytes, etc.) are static and share a static sBufferSize; no instance is needed and the constructor only blocks instantiation, per the library-wide *Utils convention.","triggerScenarios":"Reflective construction via getDeclaredConstructor().newInstance() with setAccessible, or a framework that new-ups classes by Class reference. A direct `new FileIOUtils()` fails to compile because the constructor is private.","commonSituations":"Coverage tooling that instantiates all classes; DI containers scanning packages; a developer who assumes instance methods; reflective test harnesses that exercise all constructors.","solutions":["Use the static API directly: FileIOUtils.writeFileFromBytes(...), FileIOUtils.readFile2Bytes(...), etc.","Exclude final utility classes from any reflective instantiation framework.","In a contract test, assert UnsupportedOperationException is thrown by the reflected constructor."],"exampleFix":"// before (reflection)\nFileIOUtils f = FileIOUtils.class.getDeclaredConstructor().newInstance();\n\n// after\nFileIOUtils.writeFileFromBytes(path, bytes, true);","handlingStrategy":"validation","validationCode":"// Never construct FileIOUtils; it is static-only.\nif (clazz == FileIOUtils.class || Modifier.isFinal(clazz.getModifiers())) {\n    // skip instantiation; use FileIOUtils.xxx() statically\n}","typeGuard":"if (clazz.getName().endsWith(\"Utils\") && Modifier.isFinal(clazz.getModifiers())) {\n    // static-only; do not newInstance()\n}","tryCatchPattern":"try {\n    Constructor<?> c = FileIOUtils.class.getDeclaredConstructor();\n    c.setAccessible(true);\n    c.newInstance();\n} catch (UnsupportedOperationException e) {\n    // expected; use FileIOUtils.xxx() instead\n}","preventionTips":["FileIOUtils is static-only — never instantiate via `new` or reflection.","Exclude final 'Utils' classes from coverage/DI/mutation tools that construct everything.","Call FileIOUtils.writeFileFromBytes()/readFile2Bytes() statically."],"tags":["utility-class","instantiation","design-pattern","reflection","file-io"],"backgroundTag":null,"analyzedSha":"7b4caf9e5440046b3fefb63b6b6e2ead7ebaf809","analyzedAt":"2026-08-14T02:26:54.956Z","schemaVersion":2},"datasetVersion":"2026-08-14T05:17:29.042Z"}