注释匿名内部类

Question

Is there a way to annotate an anonymous inner class in Java?

In this example could you add a class level annotation to Class2?

public void method1() {
  add(new Class2() {
    public void method3() {}
  });
}

Answer 1

No. You'd need to promote it to a "proper" class. It can still be scoped within the outer class if necessary, so it doesn't need to be a top-level class, or public, or whatever. But it does need a proper class definition to attach the annotation to.

Answer 2

Not yet. This feature is suggested by JSR 308 , and may be included in future versions of Java.

Answer 3

Yes, as mentioned by yegor256 , it is possible, since JDK 8 adopted JSR 308 (type annotations) .

So now whenever an annotation is decorated by @Target({ElementType.TYPE_USE}) , it can be used for annotating an anonymous class at runtime. For instance:

@Target({ ElementType.TYPE_USE })
@Retention(RetentionPolicy.RUNTIME)
@interface MyAnnotation {
    String value();
}

Object o = new @MyAnnotation("Hello") Object() {};

The tricky part is how to access the annotation:

    Class<?> c = o.getClass();
    AnnotatedType type = c.getAnnotatedSuperclass();
    System.out.println(Arrays.toString(type.getAnnotations()));