What causes "u can't instantiate me..." in Blankj/AndroidUtilCode?

Call the static API: ThrowableUtils.getFullStackTrace(throwable) instead of constructing.

Blankj/AndroidUtilCode · error · UnsupportedOperationException

u can't instantiate me...

Error message

u can't instantiate me...

What it means

ThrowableUtils is a utility class for rendering full stack traces (including cause chains). Its private constructor throws UnsupportedOperationException to block instantiation. Every public method (getFullStackTrace, etc.) is static, so the class is a namespace, not an instantiable type.

Source

Thrown at lib/utilcode/src/main/java/com/blankj/utilcode/util/ThrowableUtils.java:22

import java.io.StringWriter;
import java.util.ArrayList;
import java.util.List;
import java.util.StringTokenizer;

/**
 * <pre>
 *     author: Blankj
 *     blog  : http://blankj.com
 *     time  : 2019/02/12
 *     desc  : utils about exception
 * </pre>
 */
public class ThrowableUtils {

    private static final String LINE_SEP = System.getProperty("line.separator");

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

    public static String getFullStackTrace(Throwable throwable) {
        final List<Throwable> throwableList = new ArrayList<>();
        while (throwable != null && !throwableList.contains(throwable)) {
            throwableList.add(throwable);
            throwable = throwable.getCause();
        }
        final int size = throwableList.size();
        final List<String> frames = new ArrayList<>();
        List<String> nextTrace = getStackFrameList(throwableList.get(size - 1));
        for (int i = size; --i >= 0; ) {
            final List<String> trace = nextTrace;
            if (i != 0) {
                nextTrace = getStackFrameList(throwableList.get(i - 1));
                removeCommonFrames(trace, nextTrace);
            }
            if (i == size - 1) {

View on GitHub (pinned to 7b4caf9e54)

Solutions

Call the static API: ThrowableUtils.getFullStackTrace(throwable) instead of constructing.
Register a Gson InstanceCreator / Jackson mixin returning a sentinel so the constructor is not invoked.
Use Mockito.mockStatic for mocking rather than instantiation.
Keep the class and constructor as-is (non-final here but constructor-protected) to preserve the guard.

Example fix

// before
ThrowableUtils tu = new ThrowableUtils();

// after
String trace = ThrowableUtils.getFullStackTrace(t);

Defensive patterns

Strategy: validation

Validate before calling

// ThrowableUtils is not final but constructor is guarded.
try {
  ThrowableUtils.class.getDeclaredConstructor();
  // present and private — treat as non-instantiable
} catch (NoSuchMethodException ignored) {}

Prevention

Use ThrowableUtils.getFullStackTrace(...) statically.
Register InstanceCreator/mixin for JSON fields.
Mock statically rather than constructing.
Treat the private throwing constructor as 'do not instantiate'.

When it happens

Trigger: Reflective instantiation via ThrowableUtils.class.getDeclaredConstructor().setAccessible(true).newInstance(), or transitively through Gson/Jackson deserialization, Mockito/PowerMock, Kotlin reflection, or a DI scan.

Common situations: Serialization frameworks binding a field to ThrowableUtils; mocking in tests; coverage tooling; accidental `new ThrowableUtils()` after a fork weakened modifiers.

Related errors

AI-assisted analysis of Blankj/AndroidUtilCode@7b4caf9e54 (2026-08-14). Data as JSON: /api/errors/31917d2604f87a1a. Report an issue: GitHub.