JEP 104: Type Annotations

AuthorsMichael Ernst, Alex Buckley
OwnerMichael Ernst
StatusClosed / Delivered
Componentspecification / language
Discussiontype dash annotations dash dev at openjdk dot java dot net
BlocksJEP 120: Repeating Annotations
Reviewed byBrian Goetz
Endorsed byBrian Goetz, Mikael Vidstedt
Created2011/09/09 20:00
Updated2020/06/01 17:38


Extend the set of annotatable locations in the syntax of the Java programming language to include names which indicate the use of a type as well as (per Java SE 5.0) the declaration of a type.


Allow development of useful pluggable type checkers that refine Java's built-in type system.


Standardization of pluggable type checkers.

Success Metrics


Java's annotation system has been an unquestioned success. Programmers can write annotations on type names which appear in the declaration of variables, methods, and classes, which are then read by enterprise frameworks for configuration purposes and by compilers/IDEs for software quality purposes. Annotations allow boilerplate to be removed from code, and enable basic errors to be detected at compile-time.

Annotations on type uses, not just type declarations, enable error detection by "pluggable type checkers" which strengthen and refine Java's built-in type system. The strengthened type system prevents, at compile-time, the kind of software quality errors which would otherwise manifest themselves at run time. Examples include null pointer errors, side effects on immutable data, race conditions, information leakage, and non-internationalized strings.


JSR 308 makes targeted, low-level changes to the grammar of the Java language to allow annotations on the names of types in most places those names can be used. This includes the names of types occurring in Java SE 7 language constructs like try-with-resources and multi-catch.

JSR 308 defines new attributes for the JVM class file format to store these annotations on type names. Finally, it makes targeted changes to the java.lang.reflect and javax.lang.model API so that annotations on specific instances of type names can be retrieved.



Risks and Assumptions