checkers.igj.quals
Annotation Type Immutable

@Documented
@Retention(value=RUNTIME)
@TypeQualifier
@SubtypeOf(value=ReadOnly.class)
public @interface Immutable

Indicates that the annotated reference is an immutable reference to an immutable object. An Immutable object cannot be modified. Its fields may be reassigned or mutated only if they are explicitly marked as Mutable or Assignable.

See the checkers manual:

IGJ Checker