java - Java 方法注释如何与方法覆盖结合使用？

Question

我有一个父类 Parent 和一个子类 Child，定义如下:

class Parent {
    @MyAnnotation("hello")
    void foo() {
        // implementation irrelevant
    }
}
class Child extends Parent {
    @Override
    foo() {
        // implementation irrelevant
    }
}

如果我获得 Child::foo 的 Method 引用，childFoo.getAnnotation(MyAnnotation.class) 会给我 @MyAnnotation？还是null？

我对注解如何或是否适用于 Java 继承更感兴趣。

Answer 1

从 http://www.eclipse.org/aspectj/doc/released/adk15notebook/annotations.html#annotation-inheritance 逐字复制:

Annotation Inheritance

It is important to understand the rules relating to inheritance of annotations, as these have a bearing on join point matching based on the presence or absence of annotations.

By default annotations are not inherited. Given the following program

        @MyAnnotation
        class Super {
          @Oneway public void foo() {}
        }

        class Sub extends Super {
          public void foo() {}
        }

Then Sub does not have the MyAnnotation annotation, and Sub.foo() is not an @Oneway method, despite the fact that it overrides Super.foo() which is.

If an annotation type has the meta-annotation @Inherited then an annotation of that type on a class will cause the annotation to be inherited by sub-classes. So, in the example above, if the MyAnnotation type had the @Inherited attribute, then Sub would have the MyAnnotation annotation.

@Inherited annotations are not inherited when used to annotate anything other than a type. A type that implements one or more interfaces never inherits any annotations from the interfaces it implements.