如何在 Java 中使用 @inherited 注解?

问题描述

我没有在 Java 中获得 @Inherited 注释.如果它自动为您继承方法，那么如果我需要以自己的方式实现该方法，那又如何呢?

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 ?

它将如何知道我的实现方式?

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

另外据说如果我不想使用它，而是以老式的 Java 方式来做，我必须实现 equals()、toString()，Object类的hashCode()方法，以及java.lang.annotation.Annotation类的注解类型方法.

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.

这是为什么呢?

即使我不知道 @Inherited 注释和过去也可以正常工作的程序，我也从未实现过这些.

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

请有人从头开始解释一下.

Please somebody explain me from the scratch about this.

推荐答案

只是没有误会:你确实问java.lang.annotation.Inherited.这是注解的注解.表示被注解的类的子类被认为与它们的超类具有相同的注解.

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.

考虑以下 2 个注释:

Consider the following 2 Annotations:

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

和

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

如果三个类是这样注释的:

If three classes are annotated like this:

@UninheritedAnnotationType
class A {
    
}

@InheritedAnnotationType
class B extends A {
    
}

class C extends B {
    
}

运行此代码

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));

会打印出类似这样的结果(取决于注解的包):

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

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

如您所见，UninheritedAnnotationType 没有被继承，但 C 从 B 继承注释 InheritedAnnotationType.

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

我不知道这与什么方法有关.

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