Question

Why the follow line produce a compile error in Java? Or how I can write the correct generics syntax?

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

该方法的签名是:

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

Eclipse的错误:

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

javac的错误:

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 returns the annotation itself - not the class of the annotation. I suspect you can just use:

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

友情链接