@InterfaceAudience.Public： 对所有工程和应用可用
@InterfaceAudience.LimitedPrivate： 仅限于某些特定工程，如Comomn，HDFS等
@InterfaceAudience.Private： 仅限于Hadoop

/**

 * Annotation to inform users of a package, class or method's intended audience.

 */

@InterfaceAudience.Public

@InterfaceStability.Evolving

public class InterfaceAudience {

  /**

   * Intended for use by any project or application.

   */

  @Documented public @interface Public {};

  /**

   * Intended only for the project(s) specified in the annotation.

   * For example, "Common", "HDFS", "MapReduce", "ZooKeeper", "HBase".

   */

  @Documented public @interface LimitedPrivate {

    String[] value();

  };

  /**

   * Intended for use only within Hadoop itself.

   */

  @Documented public @interface Private {};

  private InterfaceAudience() {} // Audience can't exist on its own

}