如何在Java中使用@inherited注释？

Question

I am not getting the @Inherited annotation in Java. If it automatically inherits the methods for you then if I need to implement the method in my own way then what about that ?

How does will it come to know my way of implementation ?

Plus it is said if I do not want to use this and do it rather in an old fashioned Java way I have to implement the the equals() , toString() , and the hashCode() methods of the Object class and also the annotation type method of the java.lang.annotation.Annotation class.

Why is that?

I have never implemented those even when I did not know about the @Inherited annotation and the programs used to work fine also .

Please somebody explain me from the scratch about this.

Answer 1

Just that there is no misunderstanding: You do ask about java.lang.annotation.Inherited . This is a annotation for annotations.It means that subclasses of annotated classes are considered having the same annotation as their superclass.

Example

Consider the following 2 Annotations:

@Inherited
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface InheritedAnnotationType {

}

and

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface UninheritedAnnotationType {

}

If three classes are annotated like this:

@UninheritedAnnotationType
class A {

}

@InheritedAnnotationType
class B extends A {

}

class C extends B {

}

running this code

System.out.println(new A().getClass().getAnnotation(InheritedAnnotationType.class));
System.out.println(new B().getClass().getAnnotation(InheritedAnnotationType.class));
System.out.println(new C().getClass().getAnnotation(InheritedAnnotationType.class));
System.out.println("_________________________________");
System.out.println(new A().getClass().getAnnotation(UninheritedAnnotationType.class));
System.out.println(new B().getClass().getAnnotation(UninheritedAnnotationType.class));
System.out.println(new C().getClass().getAnnotation(UninheritedAnnotationType.class));

will print a result similar to this (depending on the packages of the annotation):

null
@InheritedAnnotationType()
@InheritedAnnotationType()
_________________________________
@UninheritedAnnotationType()
null
null

As you can see UninheritedAnnotationType is not inherited but C inherits annotation InheritedAnnotationType from B .

I don't know what methods have to do with that.