java元注解@Inherited的使用详解

1.先看源码文档

/**
* Indicates that an annotation type is automatically inherited. If
* an Inherited meta-annotation is present on an annotation type
* declaration, and the user queries the annotation type on a class
* declaration, and the class declaration has no annotation for this type,
* then the class's superclass will automatically be queried for the
* annotation type. This process will be repeated until an annotation for this
* type is found, or the top of the class hierarchy (Object)
* is reached. If no superclass has an annotation for this type, then
* the query will indicate that the class in question has no such annotation.
*
* <p>Note that this meta-annotation type has no effect if the annotated
* type is used to annotate anything other than a class. Note also
* that this meta-annotation only causes annotations to be inherited
* from superclasses; annotations on implemented interfaces have no
* effect.
*
* @author Joshua Bloch
* @since 1.5
* @jls 9.6.3.3 @Inherited
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
public @interface Inherited {
}

上述代码注释部分可以用谷歌翻译 * 大致意思是

表示注释类型自动继承。 如果在注释类型声明中存在继承的元注释，并且用户在类声明上查询注释类型，并且类声明没有此类型的注释，则该类的超类将自动查询注释类型。 将重复此过程，直到找到此类型的注释，或者达到类层次结构（Object）的顶部。 如果没有超类具有此类型的注释，则查询将指示所讨论的类没有这样的注释。

请注意，如果使用注释类型来注释除类之外的任何内容，则此元注释类型不起作用。 还要注意，这个元注释只会导致从超类继承注释; 已实现的接口上的注释无效。

通过上述描述可知，使用该注解的注解父类的子类可以继承父类的注解。

2.代码测试

2.1拥有@Inherited注解

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

String value();
}

@InheritedTest("拥有Inherited")
public class Person {

public void method(){
 }

public void method2(){
 }
}

public class Student extends Person {
}

测试：

public class TestInherited {

public static void main(String[] args) {
   Class<Student> studentClass = Student.class;
   if (studentClass.isAnnotationPresent(InheritedTest.class)){
     System.out.println(studentClass.getAnnotation(InheritedTest.class).value());
   }

}
}

输出：

2.2未拥有@Inherited注解

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface IsNotInherited {
 String value();
}

@IsNotInherited("未拥有Inherited")
public class Person {

public void method(){
 }

public void method2(){
 }
}

public class Student extends Person {
}

测试:

public class TestInherited {

public static void main(String[] args) {
   Class<Student> studentClass = Student.class;
   if (studentClass.isAnnotationPresent(IsNotInherited.class)){
     System.out.println(studentClass.getAnnotation(IsNotInherited.class).value());
   }

}
}

没有输出任何任容，由此可知未拥有@Inherited注解的注解的类的子类不会被继承该注解。

来源：https://segmentfault.com/a/1190000021123395