Java元编程难题:获取本身由给定注释A注释的所有注释

Question

你认为你是一个java向导吗？

您是否精通反射API的秘密？

public @interface @a {}
public @interface @b {}
@Mark public @interface @c {}    
@Mark public @interface @d {}
public @interface @e {}

public Class C
{
    @a @b @c @d @e public void x();
}

public class Solver
{
    public Annotation[] solve(Method m, Class c);
}

你必须编写方法求解,所以如果在方法Cx()和Mark.class上调用它,它将返回{c,d}.

(这不是家庭作业,是我正在尝试开发的框架元编程框架的真正编程任务)

Answer 1

这是经过测试的.它确实比应该的更难.

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface a{}

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface b{}

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.ANNOTATION_TYPE})
public @interface Mark{}

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
@Mark
public @interface c{}

public static class D {
    @a @b @c
    public void x() {}
}

public static void main(String[] args) throws Exception {
    Method m = D.class.getMethod("x");

    Collection<Annotation> ret = new HashSet<Annotation>();
    Annotation[] annotations = m.getAnnotations();
    for (Annotation annotation : annotations) {
        Annotation subAnnots = annotation.annotationType().getAnnotation(Mark.class);
        if (subAnnots != null) {
            ret.add(annotation);
        }
    }
    System.out.println(ret);
}

我想它只是引出了为什么annotationType()工作的问题,但是getClass()没有.