"Java Type Use annotation - 如何阅读它们"

Question

我正在使用自定义类型使用注释。 我无法像任何其他常规注释一样从对象中读取它们：

public class TestingAnnotations {



public static void main(final String[] args) {
     final @CustomAnnotation TypeAnnotated b = new @CustomAnnotation TypeAnnotated();
     System.out.println(b.getClass().getAnnotation(CustomAnnotation.class)); //<-- prints null :(
   }
}

@Target({ElementType.TYPE_USE, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@interface CustomAnnotation {

}

class TypeAnnotated {

}

Answer 1

你实际上没有注释类......一个类看起来像是注释：

@CustomAnnotation
class TypeAnnotated {

}

之后你会得到注释：

TypeAnnotated b = new TypeAnnotated();
System.out.println(b.getClass().getAnnotation(CustomAnnotation.class));

Answer 2

看起来您实际上想要一个本地变量注释

@Target({ElementType.TYPE_USE, ElementType.LOCAL_VARIABLE})
public @interface CustomAnnotation {
}