NumberFormat provides a number of methods to get a NumberFormat back. For example, you can use getCurrencyInstance to get one back for currency. None of these methods indicate what objects you'll get back when you invoke parseObject. This is made even more confusing by the fact that the return type may vary. For example, currency instance appears to return Long if passed in something like '$1.00' but double if passed in '$1.01'. This is unexpected and should most definitely be documented.