Blankj/AndroidUtilCode · error · IllegalArgumentException

Array has incompatible type: {}

Error message

Array has incompatible type: {}

What it means

Thrown by ArrayUtils.toString when the argument is non-null but not one of the supported array types (Object[], boolean[], byte[], char[], short[], int[], long[], float[], double[]). The method dispatches on instanceof for each array kind and throws as a terminal fallback. null is handled separately (returns "null").

Source

Thrown at lib/utilcode/src/main/java/com/blankj/utilcode/util/ArrayUtils.java:2137

            return Arrays.deepToString((Object[]) array);
        } else if (array instanceof boolean[]) {
            return Arrays.toString((boolean[]) array);
        } else if (array instanceof byte[]) {
            return Arrays.toString((byte[]) array);
        } else if (array instanceof char[]) {
            return Arrays.toString((char[]) array);
        } else if (array instanceof double[]) {
            return Arrays.toString((double[]) array);
        } else if (array instanceof float[]) {
            return Arrays.toString((float[]) array);
        } else if (array instanceof int[]) {
            return Arrays.toString((int[]) array);
        } else if (array instanceof long[]) {
            return Arrays.toString((long[]) array);
        } else if (array instanceof short[]) {
            return Arrays.toString((short[]) array);
        }
        throw new IllegalArgumentException("Array has incompatible type: " + array.getClass());
    }

    public interface Closure<E> {
        void execute(int index, E item);
    }
}

View on GitHub (pinned to 7b4caf9e54)

Solutions

1. Use String.valueOf(obj) or obj.toString() for non-array objects.
2. Convert collections to arrays: ArrayUtils.toString(list.toArray()).
3. Add an isArray() guard and branch to a non-array path.
4. Prefer Arrays.toString / Arrays.deepToString directly when you already have a typed array.

Example fix

// before
String s = ArrayUtils.toString("hello"); // Array has incompatible type: class String

// after
String s = (obj == null) ? "null" : obj.toString();

String s = (array == null)
    ? "null"
    : (array.getClass().isArray() ? ArrayUtils.toString(array) : String.valueOf(array));

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

try {
    s = ArrayUtils.toString(obj);
} catch (IllegalArgumentException e) {
    s = String.valueOf(obj);
}

When it happens

Trigger: Calling toString on a scalar Object (String, Integer, custom POJO) or a Collection instead of an array. The method is array-specific; it is not a general Object.toString replacement.

Common situations: Using ArrayUtils.toString as a generic debug printer for arbitrary objects; passing a List instead of list.toArray(); feeding boxed primitives from deserialized JSON.

Related errors

• Not an array: {}
• Index: {}, array1 Length: {}
• Index: {}, Length: 0
• Index: {}, Length: {}
• Unsupported object type: {}

AI-assisted analysis of Blankj/AndroidUtilCode@7b4caf9e54 (2026-08-14). Data as JSON: /api/errors/00dd0c2d611cec83. Report an issue: GitHub.