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   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   * This code is free software; you can redistribute it and/or modify it
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   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
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   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
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   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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   */
  
  package java.security.acl;
  
  import java.util.Enumeration;
  import java.security.Principal;
  
  /**
   * This interface is used to represent a group of principals. (A principal
   * represents an entity such as an individual user or a company). <p>
   *
   * Note that Group extends Principal. Thus, either a Principal or a Group can
   * be passed as an argument to methods containing a Principal parameter. For
   * example, you can add either a Principal or a Group to a Group object by
   * calling the object's {@code addMember} method, passing it the
   * Principal or Group.
   *
   * @author      Satish Dharmaraj
   */
  public interface Group extends Principal {
  
      /**
       * Adds the specified member to the group.
       *
       * @param user the principal to add to this group.
       *
       * @return true if the member was successfully added,
       * false if the principal was already a member.
       */
      public boolean addMember(Principal user);
  
      /**
       * Removes the specified member from the group.
       *
       * @param user the principal to remove from this group.
       *
       * @return true if the principal was removed, or
       * false if the principal was not a member.
       */
      public boolean removeMember(Principal user);
  
      /**
       * Returns true if the passed principal is a member of the group.
       * This method does a recursive search, so if a principal belongs to a
       * group which is a member of this group, true is returned.
       *
       * @param member the principal whose membership is to be checked.
       *
       * @return true if the principal is a member of this group,
       * false otherwise.
       */
      public boolean isMember(Principal member);
  
  
      /**
       * Returns an enumeration of the members in the group.
       * The returned objects can be instances of either Principal
       * or Group (which is a subclass of Principal).
       *
       * @return an enumeration of the group members.
       */
      public Enumeration<? extends Principal> members();
  
  }
  