How to get annotation values in java reflection

I have class Person:

@Retention(RetentionPolicy.RUNTIME)
@interface MaxLength {
int length();
}

@Retention(RetentionPolicy.RUNTIME)
@interface NotNull {

}

public class Person {

private int age;

private String name;

public Person(int age, String name) {
    this.age = age;
    this.name = name;
}

@NotNull
public int getAge() {
    return this.age;
}

@MaxLength(length = 3)
public String getName() {
    return this.name;
}


}

Then I'm trying to print annotation values of methods of Peson object.

 for (Method method : o.getClass().getDeclaredMethods()) {
        if (method.getName().startsWith("get")) {
            Annotation[] annotations = method.getDeclaredAnnotations();
            for (Annotation a : annotations) {
              Annotation annotation = method.getAnnotation(a.getClass());
                    System.out.println(method.getName().substring(3) + " " +
                           annotation);
            }
        }
    }

I want it to print annotation values, but it prints null. I m not quite understand what am I doing wrong.