java-annotations-retention-policy

preview

Enum Constant	Description	Example
SOURCE	Annotations are to be discarded by the compiler.	@Override, @SuppressWarnings
CLASS	Annotations are to be recorded in the class file by the compiler but need not be retained by the VM at run time.	lombok @NonNull
RUNTIME	Annotations are to be recorded in the class file by the compiler and retained by the VM at run time, so they may be read reflectively.	@Deprecated, @Target, @FunctionalInterface

project description

We will provide examples with tests for each row of the table above.

1. SourcePolicy
   • java code

     @SuppressWarnings("unchecked")
     class SourcePolicy {
     }
     

   • compiled code

     class SourcePolicy {
         SourcePolicy() {
         }
     }
     

   • tests

     assertThat(SourcePolicy.class.getAnnotations(), arrayWithSize(0));
     

2. ClassPolicy
   • java code

     class ClassPolicy {
         @NonNull
         String nonNullField;
     }
     

   • compiled code

     class ClassPolicy {
         @NonNull
         String nonNullField;
     
         ClassPolicy() {
         }
     }
     

   • tests

     assertThat(ClassPolicy.class.getAnnotations(), arrayWithSize(0));
     

3. RuntimePolicy
   • java code

     @Deprecated
     class RuntimePolicy {
     }
     

   • compiled code

     @Deprecated
     class RuntimePolicy {
         RuntimePolicy() {
         }
     }
     

   • tests

     assertThat(RuntimePolicy.class.getAnnotations(), arrayWithSize(1));
     assertEquals(Deprecated.class, RuntimePolicy.class.getAnnotations()[0].annotationType());