Blankj/AndroidUtilCode · error · UnsupportedOperationException

u can't instantiate me...

Error message

u can't instantiate me...

What it means

ScreenUtils is a final utility class whose only constructor is private and throws UnsupportedOperationException. The class exposes only static methods for screen dimensions/orientation, so it must never be instantiated. The throw is a guard: it fires the moment anything bypasses compile-time access control and invokes the constructor via reflection.

Source

Thrown at lib/utilcode/src/main/java/com/blankj/utilcode/util/ScreenUtils.java:35

import android.view.Surface;
import android.view.View;
import android.view.Window;
import android.view.WindowManager;

import static android.Manifest.permission.WRITE_SETTINGS;

/**
 * <pre>
 *     author: Blankj
 *     blog  : http://blankj.com
 *     time  : 2016/08/02
 *     desc  : utils about screen
 * </pre>
 */
public final class ScreenUtils {

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

    /**
     * Return the width of screen, in pixel.
     *
     * @return the width of screen, in pixel
     */
    public static int getScreenWidth() {
        WindowManager wm = (WindowManager) Utils.getApp().getSystemService(Context.WINDOW_SERVICE);
        if (wm == null) return -1;
        Point point = new Point();
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
            wm.getDefaultDisplay().getRealSize(point);
        } else {
            wm.getDefaultDisplay().getSize(point);
        }
        return point.x;
    }

View on GitHub (pinned to 7b4caf9e54)

Solutions

  1. Do not instantiate ScreenUtils — call its static methods directly, e.g. ScreenUtils.getScreenWidth().
  2. If a serialization framework tries to build it, add a TypeAdapter/InstanceCreator (Gson) or a mixin (Jackson) that returns null or a sentinel rather than invoking the constructor.
  3. If a mock framework is the culprit, configure it with Mockito.mockStatic (Mockito 3.4+) or use PowerMock on the static method rather than constructing the class.
  4. If you genuinely need an instance, subclass or wrap the static API behind your own injectable component instead of breaking the constructor.

Example fix

// before (Gson tries to construct the field type)
public class Config { ScreenUtils screen; }
new Gson().fromJson(json, Config.class);

// after
public class Config { int screenWidth; }
int w = ScreenUtils.getScreenWidth();
Defensive patterns

Strategy: validation

Validate before calling

// Before any reflective construction, check it is not a static-only utility.
if (Modifier.isFinal(ScreenUtils.class.getModifiers())
    && ScreenUtils.class.getDeclaredConstructors()[0].getParameterCount() == 0) {
  throw new IllegalStateException("ScreenUtils is a static utility; do not instantiate.");
}

Prevention

When it happens

Trigger: Triggered when code calls ScreenUtils.class.getDeclaredConstructor().setAccessible(true).newInstance() (directly or transitively). Common transitive causes: Gson/Jackson deserializing into a ScreenUtils field, Mockito/PowerMock attempting to instantiate the class for mocking, Kotlin reflection, or a DI container scanning the classpath.

Common situations: Unit tests where a test runner or mock framework tries to construct utility classes; JSON deserialization that maps a field to ScreenUtils; accidental `new ScreenUtils()` after removing the final keyword in a fork; code-coverage tools (JaCoCo) generating reflective probes.

Related errors

AI-assisted analysis of Blankj/AndroidUtilCode@7b4caf9e54 (2026-08-14). Data as JSON: /api/errors/a3694d4bf118d6f7. Report an issue: GitHub.