Reflection geting value from method argument annotation

Sample code:

public interface TestClass {

    @AnnoTest
    public Object getTestObject( @AnnoTestArg("id") Integer postId );

}

How can i get value from @AnnoTestArg annotation ? I know how to check is argument annotated but, i can't check annotation value.

That's my code:

public void build(...) {
    Annotation[][] anno = pm.getMethod().getParameterAnnotations();

    for( Annotation a : anno[argNumber] ) {
        if( a.equals(AnnoTestArg.class) ) {
            // value ?
        }
    }


    return connector;
}