if I call getAnnotation() on the same Field with the same Class<? extends Annotation> as parameter, will the result always be the same instance of the annotation’s class?
I know that Annotations are cached, but is there something that might clear the cache/something that might make it risky to rely on this instance?
Answer
Yes. If you look at the source code for getAnnotation it reads as follows:
public <T extends Annotation> T getAnnotation(Class<T> annotationClass) {
if (annotationClass == null)
throw new NullPointerException();
return (T) declaredAnnotations().get(annotationClass);
}
the declaredAnnotations method is coded like:
private synchronized Map<Class<? extends Annotation>, Annotation> declaredAnnotations() {
if (declaredAnnotations == null) {
declaredAnnotations = AnnotationParser.parseAnnotations(
annotations, sun.misc.SharedSecrets.getJavaLangAccess().
getConstantPool(getDeclaringClass()),
getDeclaringClass());
}
return declaredAnnotations;
}
And the declaredAnnotations field is a map:
private transient Map<Class<? extends Annotation>, Annotation> declaredAnnotations;
In summary, the annotations are stored in the map, and the same ones are returned once they have been retrieved.