Blankj/AndroidUtilCode · info · UnsupportedOperationException

u can't instantiate me...

Error message

u can't instantiate me...

What it means

GsonUtils is a final utility class whose private constructor throws UnsupportedOperationException("u can't instantiate me..."). It wraps Gson via static methods backed by a static ConcurrentHashMap of Gson instances (default, delegate, logUtils); all access is static, so no instance is needed and the constructor only blocks instantiation, per the library-wide *Utils convention.

Source

Thrown at lib/utilcode/src/main/java/com/blankj/utilcode/util/GsonUtils.java:36

/**
 * <pre>
 *     author: Blankj
 *     blog  : http://blankj.com
 *     time  : 2018/04/05
 *     desc  : utils about gson
 * </pre>
 */
public final class GsonUtils {

    private static final String KEY_DEFAULT   = "defaultGson";
    private static final String KEY_DELEGATE  = "delegateGson";
    private static final String KEY_LOG_UTILS = "logUtilsGson";

    private static final Map<String, Gson> GSONS = new ConcurrentHashMap<>();

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

    /**
     * Set the delegate of {@link Gson}.
     *
     * @param delegate The delegate of {@link Gson}.
     */
    public static void setGsonDelegate(Gson delegate) {
        if (delegate == null) return;
        GSONS.put(KEY_DELEGATE, delegate);
    }

    /**
     * Set the {@link Gson} with key.
     *
     * @param key  The key.
     * @param gson The {@link Gson}.
     */

View on GitHub (pinned to 7b4caf9e54)

Solutions

  1. Use the static API directly: GsonUtils.setGsonDelegate(gson), GsonUtils.toJson(obj), GsonUtils.fromJson(json, type), etc.
  2. Configure Gson globally via setGsonDelegate rather than per-instance.
  3. Exclude final utility classes from any reflective instantiation framework.

Example fix

// before (reflection)
GsonUtils gu = GsonUtils.class.getDeclaredConstructor().newInstance();

// after
GsonUtils.setGsonDelegate(new GsonBuilder().disableHtmlEscaping().create());
String json = GsonUtils.toJson(obj);
Defensive patterns

Strategy: validation

Validate before calling

// Never construct GsonUtils; it is static-only.
if (clazz == GsonUtils.class || Modifier.isFinal(clazz.getModifiers())) {
    // skip instantiation; use GsonUtils.xxx() statically
}

Type guard

if (clazz.getName().endsWith("Utils") && Modifier.isFinal(clazz.getModifiers())) {
    // static-only; do not newInstance()
}

Try / catch

try {
    Constructor<?> c = GsonUtils.class.getDeclaredConstructor();
    c.setAccessible(true);
    c.newInstance();
} catch (UnsupportedOperationException e) {
    // expected; use GsonUtils.xxx() instead
}

Prevention

When it happens

Trigger: Reflective construction via getDeclaredConstructor().newInstance() with setAccessible, or a framework that new-ups classes by Class reference. A direct `new GsonUtils()` fails to compile because the constructor is private.

Common situations: Coverage tooling that instantiates all classes; DI containers scanning packages; a developer who assumes per-instance Gson configuration; reflective test harnesses that exercise all constructors.

Related errors

AI-assisted analysis of Blankj/AndroidUtilCode@7b4caf9e54 (2026-08-14). Data as JSON: /api/errors/54eab6284858f4d9. Report an issue: GitHub.