zhisheng17/flink-learning · error · IllegalArgumentException

The given argument is no array.

Error message

The given argument is no array.

What it means

StringUtils.arrayToString renders an array (primitive or object) as a string. After trying all known array component types it falls back: if the object is not an array at all, it throws IllegalArgumentException('The given argument is no array.').

Source

Thrown at flink-learning-core/src/main/java/com/zhisheng/core/utils/StringUtils.java:166

			return Arrays.toString((double[]) array);
		}
		if (array instanceof float[]) {
			return Arrays.toString((float[]) array);
		}
		if (array instanceof boolean[]) {
			return Arrays.toString((boolean[]) array);
		}
		if (array instanceof char[]) {
			return Arrays.toString((char[]) array);
		}
		if (array instanceof short[]) {
			return Arrays.toString((short[]) array);
		}

		if (array.getClass().isArray()) {
			return "<unknown array type>";
		} else {
			throw new IllegalArgumentException("The given argument is no array.");
		}
	}

	/**
	 * Replaces control characters by their escape-coded version. For example,
	 * if the string contains a line break character ('\n'), this character will
	 * be replaced by the two characters backslash '\' and 'n'. As a consequence, the
	 * resulting string will not contain any more control characters.
	 *
	 * @param str The string in which to replace the control characters.
	 * @return The string with the replaced characters.
	 */
	public static String showControlCharacters(String str) {
		int len = str.length();
		StringBuilder sb = new StringBuilder();

		for (int i = 0; i < len; i += 1) {
			char c = str.charAt(i);

View on GitHub (pinned to d731cee761)

Solutions

1. Pass an actual array (e.g. Object[], int[]) to arrayToString
2. Convert collections first: list.toArray()
3. Use arrayAwareToString which handles non-array objects by falling back to String.valueOf

Example fix

// before
StringUtils.arrayToString(myList);
// after
StringUtils.arrayAwareToString(myList); // or myList.toArray()

if (obj == null || !obj.getClass().isArray()) {
    throw new IllegalArgumentException("arrayToString requires an array, got: " + (obj == null ? "null" : obj.getClass().getSimpleName()));
}

static boolean isArray(Object o) {
    return o != null && o.getClass().isArray();
}

try {
    String s = StringUtils.arrayToString(arg);
} catch (IllegalArgumentException e) {
    if ("The given argument is no array.".equals(e.getMessage())) {
        s = String.valueOf(arg);
    } else throw e;
}

When it happens

Trigger: Calling arrayToString (directly or via arrayAwareToString) with a non-array object such as a String, List, or Integer — the method requires Class.isArray() to be true.

Common situations: Passing a List or Collection expecting it to be formatted like an array, or after a refactor changed a parameter from T[] to List<T> while the call site still calls arrayToString.

Understand the failure class

Background: "must be a positive integer", "cannot be empty", "invalid argument": how invalid-argument errors work across open-source libraries — this error's family across 33 libraries.

Related errors

• bytes == null
• No measurement defined
• text does not start with a number
• The value '${number}' cannot be re represented as 64bit numb
• kubernetes.cluster-id must not be blank.

AI-assisted analysis of zhisheng17/flink-learning@d731cee761 (2026-09-06). Data as JSON: /api/errors/6811d791fff8f2c8. Report an issue: GitHub.