Blankj/AndroidUtilCode · info · UnsupportedOperationException

u can't instantiate me...

Error message

u can't instantiate me...

What it means

FileUtils is a final utility class whose private constructor throws UnsupportedOperationException("u can't instantiate me..."). All file operations (getFileByPath, createOrExistsFile, copy, delete, listFilesInDir, etc.) are static; the constructor exists only to prevent instantiation, consistent with the library-wide *Utils pattern.

Source

Thrown at lib/utilcode/src/main/java/com/blankj/utilcode/util/FileUtils.java:42

import java.util.Comparator;
import java.util.List;

import javax.net.ssl.HttpsURLConnection;

/**
 * <pre>
 *     author: Blankj
 *     blog  : http://blankj.com
 *     time  : 2016/05/03
 *     desc  : utils about file
 * </pre>
 */
public final class FileUtils {

    private static final String LINE_SEP = System.getProperty("line.separator");

    private FileUtils() {
        throw new UnsupportedOperationException("u can't instantiate me...");
    }

    /**
     * Return the file by path.
     *
     * @param filePath The path of file.
     * @return the file
     */
    public static File getFileByPath(final String filePath) {
        return UtilsBridge.isSpace(filePath) ? null : new File(filePath);
    }

    /**
     * Return whether the file exists.
     *
     * @param file The file.
     * @return {@code true}: yes<br>{@code false}: no
     */

View on GitHub (pinned to 7b4caf9e54)

Solutions

  1. Call the static API directly: FileUtils.getFileByPath(...), FileUtils.createOrExistsFile(...), etc.
  2. Add FileUtils to the exclusion list of any tool that reflectively instantiates classes.
  3. For a contract test, expect UnsupportedOperationException from the reflected constructor.

Example fix

// before (reflection)
FileUtils fu = FileUtils.class.getDeclaredConstructor().newInstance();

// after
File f = FileUtils.getFileByPath("/sdcard/test.txt");
Defensive patterns

Strategy: validation

Validate before calling

// Never construct FileUtils; it is static-only.
if (clazz == FileUtils.class || Modifier.isFinal(clazz.getModifiers())) {
    // skip instantiation; use FileUtils.xxx() statically
}

Type guard

if (clazz.getName().endsWith("Utils") && Modifier.isFinal(clazz.getModifiers())) {
    // static-only; do not newInstance()
}

Try / catch

try {
    Constructor<?> c = FileUtils.class.getDeclaredConstructor();
    c.setAccessible(true);
    c.newInstance();
} catch (UnsupportedOperationException e) {
    // expected; use FileUtils.xxx() instead
}

Prevention

When it happens

Trigger: Reflective instantiation via getDeclaredConstructor().newInstance() with setAccessible, or passing the Class to a reflective factory/coverage tool. A normal `new FileUtils()` is a compile error because the constructor is private.

Common situations: Coverage/quality tools that instantiate every class; DI or reflective object mappers; a developer who expects instance state; service loaders that scan packages.

Related errors

AI-assisted analysis of Blankj/AndroidUtilCode@7b4caf9e54 (2026-08-14). Data as JSON: /api/errors/442510182c99f074. Report an issue: GitHub.