为什么 getAnnotation 不接受 Class<？扩展注释>

Question

为什么后续行会在 Java 中产生编译错误？或者我怎样才能写出正确的泛型语法？

Class<? extends Annotation> annotation = annotations[i];
Class<? extends Annotation> anno = javaClass.getAnnotation(annotation);

方法的签名是：

public <A extends Annotation> A getAnnotation(Class<A> annotationClass)

来自 Eclipse 的编译错误：

Type mismatch: cannot convert from capture#5-of ? extends Annotation to Class<? extends Annotation>

从 javac 编译错误：

incompatible types
    Class<? extends Annotation> anno = javaClass.getAnnotation(annotation);
                                                              ^
 required: Class<? extends Annotation>
 found:    CAP#1
 where CAP#1 is a fresh type-variable:
   CAP#1 extends Annotation from capture of ? extends Annotation

Answer 1

getAnnotation 返回注解本身——而不是注解的类。我怀疑你可以使用：

Class<? extends Annotation> annotationClass = annotations[i];
Annotation annotation = javaClass.getAnnotation(annotationClass);