/* Permission.java -- The superclass for all permission objects
   Copyright (C) 1998 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;

import java.io.Serializable;

/**
 * This class is the abstract superclass of all classes that implement
 * the concept of a permission.  A permission consists of a permission name 
 * and optionally a list of actions that relate to the permission.  The
 * actual meaning of the name of the permission is defined only in the
 * context of a subclass.  It may name a resource to which access permissions
 * are granted (for example, the name of a file) or it might represent
 * something else entirely.  Similarly, the action list only has meaning
 * within the context of a subclass.  Some permission names may have no
 * actions associated with them.  That is, you either have the permission
 * or you don't.
 *
 * The most important method in this class is <code>implies</code>.  This
 * checks whether if one has this permission, then the specified
 * permission is also implied.  As a conceptual example, consider the
 * permissions "Read All Files" and "Read File foo".  The permission
 * "Read All Files" implies that the caller has permission to read the
 * file foo.
 *
 * <code>Permission</code>'s are not dynamic objects.  Once created, a 
 * <code>Permission</code>'s name and action list cannot be changed.
 *
 * @version 0.0
 *
 * @author Aaron M. Renn (arenn@urbanophile.com)
 */
public abstract class Permission implements Guard, Serializable
{
  /**
   * This is the name assigned to this permission object.
   */
  protected String name;	// Taken from the serializable form information

  /**
   * This method initializes a new instance of <code>Permission</code> to
   * have the specified name.
   */
  public Permission(String name)
  {
    this.name = name;
  }

  /**
   * This method returns the name of this <code>Permission</code>
   *
   * @return The name of this <code>Permission</code>
   */
  public String getName()
  {
    return (name);
  }

  /**
   * This method returns the list of actions for this <code>Permission</code>
   * as a <code>String</code>.
   *
   * @return The action list for this <code>Permission</code>.
   */
  public abstract String getActions();

  /**
   * This method implements the <code>Guard</code> interface for this class.
   * It calls the <code>checkPermission</code> method in 
   * <code>SecurityManager</code> with this <code>Permission</code> as its
   * argument.  This method returns silently if the security check succeeds
   * or throws an exception if it fails.
   *
   * @param obj The <code>Object</code> being guarded - ignored by this class
   *
   * @exception SecurityException If the security check fails
   */
  public void checkGuard(Object obj) throws SecurityException
  {
    SecurityManager sm = System.getSecurityManager();
    if (sm != null)
      sm.checkPermission(this);
  }

  /**
   * This method tests whether this <code>Permission</code> implies that the
   * specified <code>Permission</code> is also granted.
   *
   * @param perm The <code>Permission</code> to test against
   *
   * @return <code>true</code> if the specified <code>Permission</code> is implied by this one, <code>false</code> otherwise.
   */
  public abstract boolean implies(Permission perm);

  /**
   * This method returns a hash code for this <code>Permission</code>.
   *
   * @return A hash value.
   */
  public abstract int hashCode();

  /**
   * This method returns a <code>String</code> representation of this
   * <code>Permission</code> object.
   *
   * @return This object as a <code>String</code>.
   */
  public String toString()
  {
    return ("'\"" + getClass().getName() + "\" \"" + getName() +
	    "\"" + " \"" + getActions() + "\")'");
  }

  /**
   * This method returns an empty <code>PermissionCollection</code> object
   * that can store permissions of this type, or <code>null</code> if no
   * such collection is defined.
   *
   * @return A new <code>PermissionCollection</code>
   */
  public PermissionCollection newPermissionCollection()
  {
    return null;
  }
}