Annotations on Java Types

• JSR 308

• "permits annotations to appear on any use of a type, not just on class/method/field/variable declarations"

• for generic type arguments to parameterized classes:

      Map<@NonNull String, @NonEmpty List<@Readonly Document>> files;
  
  

• for generic type arguments in a generic method or constructor invocation:

      o.<@NonNull String>m("...");
  

• for type parameter bounds and wildcards:

      class Folder<F extends @Existing File> { ... }
      Collection<? super @Existing File>
  

• for class inheritance:

      class UnmodifiableList<T> implements @Readonly List<@Readonly T> { ... }
  
  

• for throws clauses:

      void monitorTemperature() throws @Critical TemperatureException { ... }
  

• for typecasts:

      myString = (@NonNull String) myObject;
  

• for type tests:

      boolean isNonNull = myString instanceof @NonNull String;
  

• for object creation:

      new @NonEmpty @Readonly List<String>(myNonEmptyStringSet)
  
  

  For generic constructors (JLS section 8.8.4), the annotation follows the explicit type arguments (JLS section 15.9):

      new <String> @Interned MyObject()
  

• for method receivers:

      public int size() @Readonly { ... }
  

• for class literals:

      Class<@NonNull String> c = @NonNull String.class;
  

• for arrays:

      Document[@Readonly][] docs4 = new Document[@Readonly 2][12];
      Document[][@Readonly] docs5 = new Document[2][@Readonly 12];