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)@Inheritedpublic @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。
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本文标题: java元注解@Inherited的使用详解
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