Blankj/AndroidUtilCode · error · UnsupportedOperationException

u can't instantiate me...

Error message

u can't instantiate me...

What it means

StringUtils is a final static-only utility for string checks and manipulation. Its private constructor throws UnsupportedOperationException to prevent instantiation. All public methods are static, so construction is a contract violation.

Source

Thrown at lib/utilcode/src/main/java/com/blankj/utilcode/util/StringUtils.java:21

import android.content.res.Resources;
import androidx.annotation.ArrayRes;
import androidx.annotation.Nullable;
import androidx.annotation.StringRes;

import java.util.IllegalFormatException;

/**
 * <pre>
 *     author: Blankj
 *     blog  : http://blankj.com
 *     time  : 2016/08/16
 *     desc  : utils about string
 * </pre>
 */
public final class StringUtils {

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

    /**
     * Return whether the string is null or 0-length.
     *
     * @param s The string.
     * @return {@code true}: yes<br> {@code false}: no
     */
    public static boolean isEmpty(final CharSequence s) {
        return s == null || s.length() == 0;
    }

    /**
     * Return whether the string is null or whitespace.
     *
     * @param s The string.
     * @return {@code true}: yes<br> {@code false}: no
     */

View on GitHub (pinned to 7b4caf9e54)

Solutions

  1. Use static methods: StringUtils.isEmpty(s) instead of constructing the class.
  2. Provide a Gson InstanceCreator / Jackson mixin returning a sentinel to avoid constructor invocation.
  3. Mock static methods with Mockito.mockStatic instead of constructing StringUtils.
  4. Keep the class final with a private constructor.

Example fix

// before
StringUtils su = new StringUtils();

// after
boolean empty = StringUtils.isEmpty(s);
Defensive patterns

Strategy: validation

Validate before calling

if (Modifier.isFinal(StringUtils.class.getModifiers())) {
  throw new IllegalStateException("StringUtils is static-only.");
}

Prevention

When it happens

Trigger: Reflective instantiation (StringUtils.class.getDeclaredConstructor().setAccessible(true).newInstance()) or transitive construction through Gson/Jackson deserialization, Mockito/PowerMock, Kotlin reflection, or a DI classpath scan.

Common situations: JSON libraries binding a field to StringUtils; test frameworks mocking utility classes; coverage probes; accidental instantiation after weakening access modifiers.

Related errors

AI-assisted analysis of Blankj/AndroidUtilCode@7b4caf9e54 (2026-08-14). Data as JSON: /api/errors/1d00fc9320b61a6d. Report an issue: GitHub.