/* Group.java -- Represents a group of Principals
   Copyright (C) 1998, 2001 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU Classpath 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 for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA.

As a special exception, if you link this library with other files to
produce an executable, this library does not by itself cause the
resulting executable to be covered by the GNU General Public License.
This exception does not however invalidate any other reasons why the
executable file might be covered by the GNU General Public License. */

package java.security.acl;

import java.security.Principal;
import java.util.Enumeration;

/**
 * This interface represents a group of <code>Principals</code>.  Note that
 * since this interface extends <code>Principal</code>, a <code>Group</code>
 * can be used where ever a <code>Principal</code> is requested.  This
 * includes arguments to the methods in this interface.
 *
 * @version 0.0
 *
 * @author Aaron M. Renn (arenn@urbanophile.com)
 */
public interface Group extends Principal
{
  /**
   * This method adds a new <code>Principal</code> to this group.
   *
   * @param user The new <code>Principal</code> to add
   *
   * @return <code>true</code> if the user was successfully added or <code>false</code> if the user is already a member
   */
  public abstract boolean addMember(Principal user);

  /**
   * This method deletes a member from the group.
   *
   * @param user The <code>Principal</code> to delete
   *
   * @return <code>true</code> if the user was successfully deleted or <code>false</code> if the user is not a member of the group
   */
  public abstract boolean removeMember(Principal user);

  /**
   * This method tests whether or not a given <code>Principal</code> is a
   * member of this group.
   *
   * @param user The <code>Principal</code> to test for membership
   *
   * @return <code>true</code> if the user is member, <code>false</code> otherwise
   */
  public abstract boolean isMember(Principal member);

  /**
   * This method returns a list of all members of the group as an 
   * <code>Enumeration</code>.
   *
   * @return The list of all members of the group
   */
  public abstract Enumeration members();
}