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JCas classes are associated with a class loader.  Except for the built-in types which always have JCas Classes, other JCas classes are optional. Furthermore, JCas classes may define only a subset of the features of the fully merged type system. So, even when a JCas class is present, it may not have getters and setters for some features of the corresponding UIMA type. These features can be accessed of course using the plain APIs (see above). 

When  When a UIMA type is instantiated in V3, the Java class used is the most specific instance of a JCas class for that type that is found.  For example, if you have a type Foo, with superType Bar, which in turn is a subtype of Annotation, and have no JCas classes defined, then when you create an instance of Foo (using the plain API: casView.createFS(fooType) because you can't do the JCas style of new Foo, because you haven't got a JCas class for type Foo), it will create an instance of Annotation as the implementing Java class.

One set of JCas classes per class loader may be used (even simultaneously) for multiple different type systems.  This can occur sequentially, for example, if in the use case where a sequence of CASs and their type systems are being deserialized and worked on, sequentially.  The type hierarchy defined by the JCas classes must match the UIMA type system(s) where it is being used.  To run using multiple different JCas definitions, class loader isolation must be used.

When generated, they are specific to one (merged) type system, except for shared, common, built-in class definitions.  To allow for multiple type systems within one JVM simultaneously, class loader isolation is used.

; it can also occur when running multiple different pipelines under one class loader. When committing a type system, a check is made for each type to see if there is a corresponding JCas class, and if found, that any defined features have the proper range.

It is possible to run multiple pipelines with non-compatible type systems and JCas classes by running each one under its own class loader; in this scenario, each pipeline will load its own copy of JCas classes from its own classloader's classpath.

Connecting Instances with Type and Feature information

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Information about types and features is stored in TypeImpl and FeatureImpl instances.  These are unique per type system.  However, multiple type system instances created using the same (merged) definition, and therefore "equal", are recognized at type system commit time, and the existing type system implementation is reused in this case.

When creating a new instance of a UIMA Type, the JCas class for that type is loaded (if not already, and if available).

 

 This is different from V2, and may require updating code which gets references to types and features prior to type system commit; that code needs to be updated to re-acquire those references after type system commit, because the Type and Feature instances may be replaced with a shared version if the type system is equal to one already committed.

Locating the corresponding UIMA Type when creating a JCas type using the "new" operator

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When a JCas instance is created using the "new" operator, it locates the type using information in a JCasRegistry.  The type cannot be statically kept in the JCas class definition, since one JCas class might be used by multiple different type systems.  Instead, each JCas class, when it is loaded, is assigned a unique incrementing number; this number is kept with the static (one per class loader) information for TypeSystemImpl.

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