// Be sure not to use getFields as that only fetches public fields.
Field[] fieldList = EntityFireworkRocket.class.getDeclaredFields();
for (int i = 0; i < fieldList.length; i++) {
    System.out.println("[" + i + "] " + fieldList[ i ]);
}
// This line is optional, but it makes it easier to find the field indexes
// by stopping Minecraft once they are printed.
FMLCommonHandler.instance().exitJava(0, true);