Create Annotation instance with defaults, in Java

Question

How can I create an instance of the following annotation (with all fields set to their default value).

    @Retention( RetentionPolicy.RUNTIME )
    public @interface Settings {
            String a() default "AAA";
            String b() default "BBB";
            String c() default "CCC";
    }

I tried new Settings(), but that does not seem to work...

Answer 1

To create an instance you need to create a class that implements:

• java.lang.annotation.Annotation
• and the annotation you want to "simulate"

For example: public class MySettings implements Annotation, Settings

But you need to pay special attention to the correct implementation of equals and hashCode according to the Annotation interface. http://download.oracle.com/javase/1.5.0/docs/api/java/lang/annotation/Annotation.html

If you do not want to implement this again and again then have a look at the javax.enterprise.util.AnnotationLiteral class. That is part of the CDI(Context Dependency Injection)-API. (@see code)

To get the default values you can use the way that is described by akuhn (former known as: Adrian). Settings.class.getMethod("a").getDefaultValue()