Blankj/AndroidUtilCode · error · UnsupportedOperationException

u can't instantiate me...

Error message

u can't instantiate me...

What it means

JsonUtils is a final utility class providing static methods for JSON inspection (isJSONObject, isJSONArray). Its private constructor throws UnsupportedOperationException to enforce that the class is never instantiated — all functionality is accessed via static calls. This is a standard Java utility-class idiom.

Source

Thrown at lib/utilcode/src/main/java/com/blankj/utilcode/util/JsonUtils.java:26

 * <pre>
 *     author: Blankj
 *     blog  : http://blankj.com
 *     time  : 2019/01/07
 *     desc  : utils about json
 * </pre>
 */
public final class JsonUtils {

    private static final byte TYPE_BOOLEAN     = 0x00;
    private static final byte TYPE_INT         = 0x01;
    private static final byte TYPE_LONG        = 0x02;
    private static final byte TYPE_DOUBLE      = 0x03;
    private static final byte TYPE_STRING      = 0x04;
    private static final byte TYPE_JSON_OBJECT = 0x05;
    private static final byte TYPE_JSON_ARRAY  = 0x06;

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

    
    /**
     * Checks if a given input is a JSONObject.
     *
     * @param input Anything.
     * @return true if it is a JSONObject.
     */
    public static <T> boolean isJSONObject(final T input) {
        return input instanceof JSONObject;
    }

    /**
     * Checks if a given input is a JSONArray
     *
     * @param input Anything.
     * @return true if it is a JSONArray.

View on GitHub (pinned to 7b4caf9e54)

Solutions

  1. Use only static methods: JsonUtils.isJSONObject(obj), JsonUtils.isJSONArray(obj). Never call new JsonUtils().
  2. If a DI/serialization framework triggers this, exclude JsonUtils from component scanning or add it to the framework's ignore list.
  3. If reflection-based testing causes it, mock individual static method calls with PowerMock/mockito-inline rather than instantiating the class.
  4. If using ProGuard/R8, ensure no keep rules or serialization configs target utility classes for instantiation.

Example fix

// before
JsonUtils utils = new JsonUtils();
boolean isObj = utils.isJSONObject(jsonStr);

// after
boolean isObj = JsonUtils.isJSONObject(jsonStr);
Defensive patterns

Strategy: type-guard

Validate before calling

// Utility classes are never instantiated — guard at the call site
if (clazz != JsonUtils.class) {
    Object instance = clazz.getDeclaredConstructor().newInstance();
}

Type guard

// Verify the target is not a utility class before reflective instantiation
static boolean isInstantiable(Class<?> clazz) {
    try {
        java.lang.reflect.Constructor<?> c = clazz.getDeclaredConstructor();
        c.setAccessible(true);
        // Can't truly guard without instantiating; instead check by convention
        return !clazz.getName().endsWith("Utils");
    } catch (NoSuchMethodException e) {
        return false;
    }
}

Try / catch

try {
    Constructor<JsonUtils> c = JsonUtils.class.getDeclaredConstructor();
    c.setAccessible(true);
    JsonUtils instance = c.newInstance();
} catch (UnsupportedOperationException e) {
    // This is a utility class — use static methods instead
    Log.w(TAG, "JsonUtils is a utility class, use static methods");
}

Prevention

When it happens

Trigger: Instantiating via reflection (Constructor.newInstance or Class.getDeclaredConstructor().newInstance()), or via frameworks that auto-instantiate classes — Gson/Jackson deserialization targeting JsonUtils, Mockito mock creation, Dagger/Guice DI scanning, or ProGuard/R8 keep rules that assume an instantiable class.

Common situations: A dependency injection graph or serialization framework scans a package and tries to construct every class; a unit test uses Mockito.mock() on the wrong target; a ProGuard keep rule references the class and a post-obfuscation reflection call attempts construction.

Related errors

AI-assisted analysis of Blankj/AndroidUtilCode@7b4caf9e54 (2026-08-14). Data as JSON: /api/errors/d4f0d266fc6585c4. Report an issue: GitHub.