public static RecordingLevel forId(int id) {
            if (id < MIN_RECORDING_LEVEL_KEY || id > MAX_RECORDING_LEVEL_KEY)
                throw new IllegalArgumentException(String.format("Unexpected RecordLevel id `%d`, it should be between `%d` " +
                    "and `%d` (inclusive)", id, MIN_RECORDING_LEVEL_KEY, MAX_RECORDING_LEVEL_KEY));
            return ID_TO_TYPE[id];
        }
the permanent and immutable id of an API--this can't change ever
clients/src/main/java/org/apache/kafka/common/metrics/Sensor.java