Blankj/AndroidUtilCode · error · UnsupportedOperationException

u can't instantiate me...

Error message

u can't instantiate me...

What it means

MapUtils is a utility class providing static factory methods for creating and populating maps (newHashMap, newUnmodifiableMap, newTreeMap, etc.) from pairs. Its private constructor throws UnsupportedOperationException to enforce static-only access.

Source

Thrown at lib/utilcode/src/main/java/com/blankj/utilcode/util/MapUtils.java:24

import java.util.Comparator;
import java.util.HashMap;
import java.util.Hashtable;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.TreeMap;

/**
 * <pre>
 *     author: blankj
 *     blog  : http://blankj.com
 *     time  : 2019/08/12
 *     desc  : utils about map
 * </pre>
 */
public class MapUtils {

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

    /**
     * Returns a new read-only map with the specified contents, given as a list of pairs
     * where the first value is the key and the second is the value.
     *
     * @param pairs a list of pairs
     * @return a new read-only map with the specified contents
     */
    @SafeVarargs
    public static <K, V> Map<K, V> newUnmodifiableMap(final Pair<K, V>... pairs) {
        return Collections.unmodifiableMap(newHashMap(pairs));
    }

    @SafeVarargs
    public static <K, V> HashMap<K, V> newHashMap(final Pair<K, V>... pairs) {
        HashMap<K, V> map = new HashMap<>();
        if (pairs == null || pairs.length == 0) {

View on GitHub (pinned to 7b4caf9e54)

Solutions

  1. Use static factory methods: MapUtils.newHashMap(pairs), MapUtils.newUnmodifiableMap(pairs). Never instantiate.
  2. Exclude utility classes from DI scanning and serialization configs.
  3. Mock static methods with mockito-inline for testing.

Example fix

// before
MapUtils mu = new MapUtils();
Map<String, Integer> map = mu.newHashMap(Pair.create("a", 1));

// after
Map<String, Integer> map = MapUtils.newHashMap(Pair.create("a", 1));
Defensive patterns

Strategy: type-guard

Validate before calling

// MapUtils is static-only — use factory methods directly
Map<String, Integer> map = MapUtils.newHashMap(
    Pair.create("a", 1), Pair.create("b", 2));

Type guard

static boolean isUtilityClass(Class<?> c) {
    return Modifier.isFinal(c.getModifiers()) && c.getSimpleName().endsWith("Utils");
}

Try / catch

try {
    MapUtils.class.getDeclaredConstructor().setAccessible(true);
    MapUtils.class.getDeclaredConstructor().newInstance();
} catch (UnsupportedOperationException e) {
    // Use static factory methods instead
}

Prevention

When it happens

Trigger: Direct or reflective instantiation by DI frameworks (Dagger, Guice, Spring), mocking libraries (Mockito, PowerMock), serialization frameworks (Gson, Jackson), or manual reflection.

Common situations: Component scanning in a DI framework traverses the utility package and attempts construction; a test suite instantiates all classes for coverage analysis; a serialization library targets the class.

Related errors

AI-assisted analysis of Blankj/AndroidUtilCode@7b4caf9e54 (2026-08-14). Data as JSON: /api/errors/383c5832fa7a77bd. Report an issue: GitHub.