How to use @inherited annotation in Java?
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
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.