java元注解@Inherited的使用详解

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 hieraojJAWJmrchy (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.

*

*

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法大致意思是

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 studentClahttp://ss = 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 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。

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