Blankj/AndroidUtilCode · error · UnsupportedOperationException

u can't instantiate me...

Error message

u can't instantiate me...

What it means

DebugUtils in the full utildebug module bootstraps the debug menu: its static initializer registers tool debugs and an activity-lifecycle callback. Its private constructor throws UnsupportedOperationException to prevent instantiation; all public methods (setIconId, addDebugs) are static and rely on the class-level init having run.

Source

Thrown at lib/utildebug/src/main/java/com/blankj/utildebug/DebugUtils.java:31

import com.blankj.utildebug.menu.DebugMenu;

import java.util.ArrayList;
import java.util.List;

import androidx.annotation.DrawableRes;

/**
 * <pre>
 *     author: blankj
 *     blog  : http://blankj.com
 *     time  : 2019/08/28
 *     desc  : utils about debug
 * </pre>
 */
public class DebugUtils {

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

    static {
        List<IDebug> debugList = new ArrayList<>();
        AbsToolDebug.addToolDebugs(debugList);
        DebugMenu.getInstance().setDebugs(debugList);
        getApp().registerActivityLifecycleCallbacks(ActivityLifecycleImpl.instance);
    }

    public static void setIconId(final @DrawableRes int icon) {
        DebugIcon.getInstance().setIconId(icon);
    }

    public static void addDebugs(final List<IDebug> debugs) {
        DebugMenu.getInstance().addDebugs(debugs);
    }

    public static Application getApp() {

View on GitHub (pinned to 7b4caf9e54)

Solutions

  1. Call the static API: DebugUtils.setIconId(res) / DebugUtils.addDebugs(list) instead of constructing.
  2. Ensure Utils.init() has run before any DebugUtils touch so its static initializer succeeds.
  3. Provide a Gson InstanceCreator / Jackson mixin returning a sentinel so the constructor is not invoked.
  4. Use Mockito.mockStatic for mocking rather than constructing DebugUtils.

Example fix

// before
DebugUtils du = new DebugUtils();

// after
DebugUtils.setIconId(R.drawable.ic_debug);
DebugUtils.addDebugs(debugItems);
Defensive patterns

Strategy: validation

Validate before calling

// Ensure the library is initialized before touching DebugUtils (static initializer needs app).
if (Utils.getApp() == null) {
  throw new IllegalStateException("Call Utils.init() before DebugUtils.");
}

Prevention

When it happens

Trigger: Reflective instantiation via DebugUtils.class.getDeclaredConstructor().setAccessible(true).newInstance(), or transitively through Gson/Jackson deserialization, Mockito/PowerMock, Kotlin reflection, or a DI scan. Instantiating also implies the static initializer (getApp()/DebugMenu setup) ran, which requires the library to be initialized.

Common situations: Serialization frameworks binding a field to DebugUtils; mock frameworks in debug tests; coverage probes; accidental `new DebugUtils()` after weakening modifiers; using DebugUtils before Utils.init() completed so the static initializer's getApp() fails.

Related errors

AI-assisted analysis of Blankj/AndroidUtilCode@7b4caf9e54 (2026-08-14). Data as JSON: /api/errors/dd8dc14fe4c5329a. Report an issue: GitHub.