What causes "u can't instantiate me..." in Blankj/AndroidUtilCode?

Initialize once in Application.onCreate via Utils.init(this) (or via UtilsFileProvider), then use Utils.getApp() instead of constructing the class.

Blankj/AndroidUtilCode · error · UnsupportedOperationException

u can't instantiate me...

Error message

u can't instantiate me...

What it means

Utils is the core initialization class for the whole AndroidUtilCode library. Its private constructor throws UnsupportedOperationException to prevent instantiation. The class holds a static Application reference (sApp) and exposes static init()/getApp(); it is the entry point all other utils depend on, so it must never be constructed.

Solutions

Initialize once in Application.onCreate via Utils.init(this) (or via UtilsFileProvider), then use Utils.getApp() instead of constructing the class.
Provide a Gson InstanceCreator / Jackson mixin returning a sentinel so the constructor is not invoked.
Use Mockito.mockStatic for mocking rather than constructing Utils.
Keep the class final with a private constructor.

Example fix

// before
Utils u = new Utils();

// after
// in Application.onCreate()
Utils.init(this);
Context ctx = Utils.getApp();

Defensive patterns

Strategy: validation

Validate before calling

if (Modifier.isFinal(Utils.class.getModifiers())) {
  throw new IllegalStateException("Utils is static-only; call Utils.init() then Utils.getApp().");
}

Prevention

Call Utils.init(application) once at startup; use Utils.getApp() thereafter.
Register UtilsFileProvider in the manifest for automatic init.
Register InstanceCreator/mixin for JSON fields typed as Utils.
Use Mockito.mockStatic for mocking rather than constructing.

When it happens

Trigger: Reflective instantiation via Utils.class.getDeclaredConstructor().setAccessible(true).newInstance(), or transitively through Gson/Jackson deserialization, Mockito/PowerMock, Kotlin reflection, or a DI scan.

Common situations: Serialization frameworks binding a field to Utils; mock frameworks in tests; coverage probes; accidental `new Utils()` after weakening modifiers. Because Utils is the library root, constructing it also implies the app never called Utils.init(app).

Related errors

AI-assisted analysis of Blankj/AndroidUtilCode@7b4caf9e54 (2026-08-14). Data as JSON: /api/errors/1472e99f09ef5e8e. Report an issue: GitHub.

Appendix: source

Thrown at lib/utilcode/src/main/java/com/blankj/utilcode/util/Utils.java:36

 *      /  /:/~/::\  /__/\   /  /\  /  /:/~/::\   _____\__\:\   __|  |:|     \__\/\:\
 *     /__/:/ /:/\:| \  \:\ /  /:/ /__/:/ /:/\:\ /__/::::::::\ /__/\_|:|____    \  \:\
 *     \  \:\/:/~/:/  \  \:\  /:/  \  \:\/:/__\/ \  \:\~~\~~\/ \  \:\/:::::/     \__\:\
 *      \  \::/ /:/    \  \:\/:/    \  \::/       \  \:\  ~~~   \  \::/~~~~      /  /:/
 *       \  \:\/:/      \  \::/      \  \:\        \  \:\        \  \:\         /__/:/
 *        \  \::/        \__\/        \  \:\        \  \:\        \  \:\        \__\/
 *         \__\/                       \__\/         \__\/         \__\/
 *     blog  : http://blankj.com
 *     time  : 16/12/08
 *     desc  : utils about initialization
 * </pre>
 */
public final class Utils {

    @SuppressLint("StaticFieldLeak")
    private static Application sApp;

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

    /**
     * Init utils.
     * <p>Init it in the class of UtilsFileProvider.</p>
     *
     * @param app application
     */
    public static void init(final Application app) {
        if (app == null) {
            Log.e("Utils", "app is null.");
            return;
        }
        if (sApp == null) {
            sApp = app;
            UtilsBridge.init(sApp);
            UtilsBridge.preLoad();
            return;

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