package checkers.quals;
import java.lang.annotation.*;
import static java.lang.annotation.ElementType.FIELD;
/**
* Declares that the field may not be accessed if the receiver is of the
* specified qualifier type (or any supertype).
*
* This property is verified by the checker that type-checks the {@code
* when} element value qualifier.
*
* <p><b>Example</b>
* Consider a class, {@code Table}, with a locking field, {@code lock}. The
* lock is used when a {@code Table} instance is shared across threads. When
* running in a local thread, the {@code lock} field ought not to be used.
*
* You can declare this behavior in the following way:
*
* <pre><code>
* class Table {
* private @Unused(when=LocalToThread.class) final Lock lock;
* ...
* }
* </code></pre>
*
* The checker for {@code @LocalToThread} would issue an error for the following code:
*
* <pre> @LocalToThread Table table = ...;
* ... table.lock ...;
* </pre>
*
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({FIELD})
public @interface Unused {
/**
* The field that is annotated with @Unused may not be accessed via a
* receiver that is annotated with the "when" annotation.
*/
Class<? extends Annotation> when();
}