In the following example, the type checked can be obtained from the generic. The generic helps ensure the type is consistent.

public static void main(String... args) { System.out.println("getTypeQualifier(MatchesPattern.Checker.class)= " + getTypeQualifier(MatchesPattern.Checker.class)); }

public static Type getTypeQualifier(Class<? extends TypeQualifierValidator> tqvClass) { for (Type type : tqvClass.getGenericInterfaces()) { if (type instanceof ParameterizedType) { ParameterizedType parameterizedType = (ParameterizedType) type; if (parameterizedType.getRawType() == TypeQualifierValidator.class) return parameterizedType.getActualTypeArguments()[1]; } } throw new AssertionError(); }

public interface TypeQualifierValidator<A extends Annotation, T> { public @Nonnull When forConstantValue(@Nonnull A annotation, T value); }

@Documented @Retention(RetentionPolicy.RUNTIME) public @interface MatchesPattern { @RegEx String value();

int flags() default 0;

static class Checker implements TypeQualifierValidator<MatchesPattern,

String> { @Nonnull public When forConstantValue(MatchesPattern annotation, String value) { Pattern p = Pattern.compile(annotation.value(), annotation.flags()); if (p.matcher(value).matches()) return When.ALWAYS; return When.NEVER; }

}

}