AnnotationProcessing_MutableAPI

Purpose/goal

Mutable API is used to:

• represent types that is going to be generated (so does not exists on the classpath yet)
• easier modification of the existing types
• manipulate with the objects instead of string representations while generating classes
• handle complex situations when more yet non-existing types should be interconnected

"Mutable" API provided by JSR 269 by default

Although TypeMirrors and Elements are not mutable (no setter are available) you still can create types using methods from javax.lang.model.util.Types class:

• WildcardType getWildcardType(TypeMirror extendsBound, TypeMirror superBound); allows you to create "custom" wildcard type like: ? extends Serializable
• DeclaredType getDeclaredType(TypeElement typeElem, TypeMirror... typeArgs); allows you to use declared type with specified type variablest, like Map<? extends Serializable, String>

So, what's the problem?

Problem is when you reach the world outside of the simple processors and want to handle more complex situations:

• create type variable with defined variable name, like <T extends Serializable> - you simply can't represent variable 'T' using the standard API
• use type variables with the declared types like PagedResult<T extends List<User>> - you can't also use it in the types
• work with classes that does not exists yet because they are going to be generated

PAP types

Mutable types

Green types from from standard PAP types are mutable.