What xml schema context is generated the method signature like "JAXBElemet<Xyz> createXyz(Xyz xyz)" of ObjectFactory by xjc?

I noticed the the simpleType or complexType is defined and the types are used in the dec开发者_JAVA技巧larations of multiple element in a schema file, the simpleType or complexType is generated a method signature as "JAXBElemet createXyz(Xyz xyz)". But I'm not sure if it is root reason.

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In order to marshal an object to XML, JAXB needs to know the name of the XML element to be used. It gets this either from (a) the @XmlRootElement annotation on the class, or (b) by wrapping the object in a JAXBElement, which contains the element name.

If XJC generates a class without @XmlRootElement, then the factory methods for that class in ObjectFactory will instead use JAXBElement wrappers, to provide the required marshalling information.

You may then ask why XJC decides to generate @XmlRootElement for some classes but not others, but that's been asked on SO before, so go and have a look around for that one.