Tests whether the given field is set. Note that the interpretation of "is set" is somewhat technical. In particular, it does not mean that the field's value is up to date. If you want to know whether a field contains an up-to-date value, you must also check areFieldsSet, making this method somewhat useless unless you're a subclass, in which case you can access the isSet array directly.

A field remains "set" from the first time its value is computed until it's cleared by one of the clear methods. Thus "set" does not mean "valid". You probably want to call get -- which will update fields as necessary -- rather than try to make use of this method.

[Android Documentation]