如果只有一个类，如何传递注释对象 <Annotation> 有空吗？

Question

Suppose there is some method like this:

void annotate(Annotation annotation);

What is the idiomatic way in java to pass an Annotation object to this method if I only have the Annotation 's Class available?

public @interface SomeAnnotation {

}

SomeAnnotation.getClass();

Answer 1

As you already mentioned annotation is just a special type of interface:

public @interface SomeAnnotation{}

Typically you actually need an "instance" of annotation usually obtained from annotated element, eg obj.getClass().getAnnotation(SomeAnnotation.class) . This returns dynamic proxy that implements interface SomeAnnotation , so all properties of annotaiton are actually methods that return current values.

If for some reason you want to simulate this functionality you can easily do it by either creating dynamic proxy yourself or even "implementing" annotation like the following:

public @interface SomeAnnotation{
    int value();
}



void annotate(new SomeAnnotation() {
    int value() {
         return 5;
    }
}

The anonymous inner class create instance of your annotation like defined here:

@SomeAnnotation(5)
public class MyClass {
}