使用默认值在另一个自定义注释中定义自定义注释

Question

I am trying to declare custom annotation in following way:

Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.METHOD})
public @interface InnerAnnotation {

}

Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.METHOD})
public @interface OuterAnnotation {
  public String default "";
  public InnerAnnotation innerAnnotation(); //here I wanted to do "public InnerAnnotation innerAnnotation() default {some default value}"
}

I wanted to use it in a way:
class first{
  @OuterAnnotation(value = "new") //wanted to declare something like this without need to define innerAnnotation
  public void func(){
  }
}

I wanted to assign some default value to inner annotation usage(so that I don't have to provide any mandatory value while using it), but some how I am not able to do that as compiler asks for compile time constant for this.Can any please suggest how to use inner annotation with any default value ?

Answer 1

The syntax for what you what is as follows:

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.METHOD})
public @interface OuterAnnotation {
    public String default "";
    public InnerAnnotation innerAnnotation() default @InnerAnnotation(); //this does the trick;  
}