Blankj/AndroidUtilCode · warning · UnsupportedOperationException

u can't instantiate me...

Error message

u can't instantiate me...

What it means

ArrayUtils is a utility class (non-final) whose private constructor throws UnsupportedOperationException. It exposes static array helpers plus the INDEX_NOT_FOUND constant; instances are intentionally forbidden.

Source

Thrown at lib/utilcode/src/main/java/com/blankj/utilcode/util/ArrayUtils.java:27

import java.util.List;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

/**
 * <pre>
 *     author: blankj
 *     blog  : http://blankj.com
 *     time  : 2019/08/10
 *     desc  : utils about array
 * </pre>
 */
public class ArrayUtils {

    public static final int INDEX_NOT_FOUND = -1;

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

    /**
     * Returns a new array only of those given elements.
     *
     * @param array The array.
     * @return a new array only of those given elements.
     */
    @NonNull
    public static <T> T[] newArray(T... array) {
        return array;
    }

    @NonNull
    public static long[] newLongArray(long... array) {
        return array;
    }

View on GitHub (pinned to 7b4caf9e54)

Solutions

  1. Use the static API, e.g. ArrayUtils.newArray(...), ArrayUtils.add(...), ArrayUtils.indexOf(...); never instantiate.
  2. Configure reflective frameworks to skip utility classes.
  3. Remove newInstance paths targeting ArrayUtils.

Example fix

// before
ArrayUtils a = reflectNew(ArrayUtils.class); // throws

// after
String[] arr = ArrayUtils.newArray("a", "b");
Defensive patterns

Strategy: validation

Validate before calling

// ArrayUtils is static-only; never instantiate.
String[] arr = ArrayUtils.newArray("a", "b");

Type guard

private static boolean isStaticUtility(Class<?> c) {
    return hasOnlyStaticMethods(c);
}

Prevention

When it happens

Trigger: Reflective instantiation or unsafe allocation of ArrayUtils instead of calling its static methods; subclassing with a public constructor is also unusual since the base constructor throws.

Common situations: Reflection/DI/serialization frameworks that build arbitrary classes; tests that reflectively scaffold utilities.

Related errors

AI-assisted analysis of Blankj/AndroidUtilCode@7b4caf9e54 (2026-08-14). Data as JSON: /api/errors/d9144ddb54b2c97d. Report an issue: GitHub.