public interface NilObject
A marker interface for nil XML elements providing an explanation about why the information is absent.
GeoAPI getter methods usually return a
If the
null value when no information is available for
a given attribute. However, it is possible to specify why an information is absent, in which case
the corresponding getter method will rather return an instance of this NilObject interface.
The information may be absent for various reasons, including the attribute being inapplicable in the metadata context
(NilReason.INAPPLICABLE), the information probably exists but is unknown to the data provider
(UNKNOW), the information may not exist at all (MISSING) or cannot be divulged (WITHHELD).
Nil objects appear most frequently in XML documents because if a mandatory ISO 19115-1 attribute
is absent, then the ISO 19115-3 standard requires us to said why it is absent. The following example
shows a CI_Citation fragment with an ordinary CI_Series element on the left side,
and an unknown CI_Series element on the right side:
Normal Series element |
Unknown Series element |
|---|---|
|
|
CI_Series element was completely omitted, then Citation.getSeries()
method would return null in Apache SIS implementation. But since a nilReason is provided,
then the SIS implementation of getSeries() will rather return an object which implement
both the Series and the NilObject interfaces, and the getNilReason() method
on that instance will return the NilReason.UNKNOWN constant.
Instantiation
Instances ofNilObject are created by first fetching the reason why the information
is missing, then invoking NilReason.createNilObject(Class). The following example
instantiates a Citation object which is nil because the information are missing:
Citation nil = NilReason.MISSING.createNilObject(Citation.class);
- Since:
- 0.3
- See Also:
-
Method Summary
Modifier and TypeMethodDescriptionReturns the reason why this object contains no information.
-
Method Details
-
getNilReason
NilReason getNilReason()Returns the reason why this object contains no information.- Returns:
- the reason why this object contains no information.
- See Also:
-