oracle/graal · error · IllegalArgumentException

Unknown class ${className} for constant${value}

Error message

Unknown class ${className} for constant${value}

What it means

Mirror of error 144 on the read side: while deserializing a primitive constant, the 'class' field in the JSON must be one of Integer, Byte, Short, Long, Float, Double. Any other class name hits the default branch and throws IllegalArgumentException naming the unknown class and raw hex value.

Source

Thrown at compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/replaycomp/JsonReplayCodec.java:484

                case "Integer" -> {
                    return Integer.parseUnsignedInt(value, HEX_RADIX);
                }
                case "Byte" -> {
                    return (byte) Integer.parseUnsignedInt(value, HEX_RADIX);
                }
                case "Short" -> {
                    return (short) Integer.parseUnsignedInt(value, HEX_RADIX);
                }
                case "Long" -> {
                    return Long.parseUnsignedLong(value, HEX_RADIX);
                }
                case "Float" -> {
                    return hexToFloat(value);
                }
                case "Double" -> {
                    return hexToDouble(value);
                }
                default -> throw new IllegalArgumentException("Unknown class " + className + " for constant" + value);
            }
        }
    }

    private static final class ResultMarkerSerializer implements ObjectSerializer {

        @Override
        public boolean serializesSubclasses() {
            return true;
        }

        @Override
        public Class<?> clazz() {
            return SpecialResultMarker.class;
        }

        @Override
        public String tag() {

View on GitHub (pinned to a66e9ccd1d)

Solutions

1. Use the same (or newer) GraalVM version to replay the file than the one that recorded it
2. Inspect the offending entry in the JSON (class/value pair from the message) and fix or remove it if the file was hand-edited
3. If you extended the writer (error 144), extend the reader switch with the matching cases

Example fix

// before
switch (className) {
    case "Integer" -> { ... }
    default -> throw new IllegalArgumentException("Unknown class " + className + ...
// after: add
    case "Boolean" -> Boolean.parseBoolean(value);
    case "Character" -> (char) Integer.parseUnsignedInt(value, HEX_RADIX);

static final Set<String> SUPPORTED_CONSTANT_CLASSES =
    Set.of("Integer", "Byte", "Short", "Long", "Float", "Double");

if (!SUPPORTED_CONSTANT_CLASSES.contains(className)) {
    throw new IllegalArgumentException("Replay file uses unsupported constant class: " + className);
}

When it happens

Trigger: Replaying a JSON replay file that contains a constant entry with a class name this codec version does not recognize — e.g. 'Boolean' written by a newer codec, or a hand-edited/garbled file.

Common situations: Version skew: file written by a GraalVM that supports more primitive classes than the reading one; manual JSON edits; truncated/corrupt replay files where the class field reads as a wrong string.

Related errors

• The replay map does not contain a tag: ${map}
• Expected a map.
• Failed to serialize ${op} due to: ${cause}
• No singleton found for ${registration}
• Invalid marker type.

AI-assisted analysis of oracle/graal@a66e9ccd1d (2026-08-14). Data as JSON: /api/errors/b7f069cbc53f4e85. Report an issue: GitHub.