Dieser Ausdruck gibt einen konstanten Wert null an.
Das Festlegen eines Wertes mit null kann hilfreich sein, um anzugeben, dass kein Wert gilt.
<?xml version="1.0" encoding="UTF-8"?> <RuleSet name="Example_null" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation= "http://www.curamsoftware.com/CreoleRulesSchema.xsd"> <Class name="Pet"> <Initialization> <Attribute name="name"> <type> <javaclass name="String"/> </type> </Attribute> </Initialization> </Class> <Class name="Person"> <!-- This Person's favorite Pet, or null if the Person owns no pet. --> <Attribute name="favoritePet"> <type> <ruleclass name="Pet"/> </type> <derivation> <specified/> </derivation> </Attribute> <!-- The name of this Person's favorite Pet, or null if the Person owns no pet. We have to test for the favoritePet being null before performing the (simple) calculation.--> <Attribute name="favoritePetsName"> <type> <javaclass name="String"/> </type> <derivation> <choose> <type> <javaclass name="String"/> </type> <when> <!-- if this Person has no favorite pet, then calculate the name of the favorite pet as null. --> <condition> <equals> <reference attribute="favoritePet"/> <null/> </equals> </condition> <value> <null/> </value> </when> <otherwise> <value> <!-- get the name of the favorite pet --> <reference attribute="name"> <reference attribute="favoritePet"/> </reference> </value> </otherwise> </choose> </derivation> </Attribute> </Class> </RuleSet>