001    /* PermissionCollection.java -- A collection of permission objects
002       Copyright (C) 1998, 2001, 2002, 2005  Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010    
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    package java.security;
039    
040    import java.io.Serializable;
041    import java.util.Enumeration;
042    
043    /**
044     * This class models a group of Java permissions.  It has convenient
045     * methods for determining whether or not a given permission is implied
046     * by any of the permissions in this collection.
047     *
048     * <p>Some care must be taken in storing permissions.  First, a collection of
049     * the appropriate type must be created.  This is done by calling the
050     * <code>newPermissionCollection</code> method on an object of the
051     * permission class you wish to add to the collection.  If this method
052     * returns <code>null</code>, any type of <code>PermissionCollection</code>
053     * can be used to store permissions of that type.  However, if a
054     * <code>PermissionCollection</code> collection object is returned, that
055     * type must be used.
056     *
057     * <p>A <code>PermissionCollection</code> returned by the
058     * <code>newPermissionCollection</code> method in a subclass of
059     * <code>Permission</code> is a homogeneous collection.  It only will
060     * hold permissions of one specified type - instances of the class that
061     * created it.  Not all <code>PermissionCollection</code> subclasses
062     * have to hold permissions of only one type however.  For example,
063     * the <code>Permissions</code> class holds permissions of many types.
064     *
065     * <p>Since the <code>newPermissionCollection</code> in <code>Permission</code>
066     * itself returns <code>null</code>, by default a permission can be stored
067     * in any type of collection unless it overrides that method to create its
068     * own collection type.
069     *
070     * @author Aaron M. Renn (arenn@urbanophile.com)
071     * @author Eric Blake (ebb9@email.byu.edu)
072     * @see Permission
073     * @see Permissions
074     * @since 1.1
075     * @status updated to 1.4
076     */
077    public abstract class PermissionCollection implements Serializable
078    {
079      /**
080       * Compatible with JDK 1.1+.
081       */
082      private static final long serialVersionUID = -6727011328946861783L;
083    
084      /**
085       * Indicates whether or not this collection is read only.
086       *
087       * @serial if the collection is read-only
088       */
089      private boolean readOnly;
090    
091      /**
092       * Create a new collection.
093       */
094      public PermissionCollection()
095      {
096      }
097    
098      /**
099       * This method adds a new <code>Permission</code> object to the collection.
100       *
101       * @param perm the <code>Permission</code> to add
102       *
103       * @throws SecurityException if the collection is marked read only
104       * @throws IllegalArgumentException if perm is of the wrong type
105       */
106      public abstract void add(Permission perm);
107    
108      /**
109       * This method tests whether the specified <code>Permission</code> object is
110       * implied by this collection of <code>Permission</code> objects.
111       *
112       * @param perm the <code>Permission</code> object to test
113       * @return true if the collection implies perm
114       */
115      public abstract boolean implies(Permission perm);
116    
117      /**
118       * This method returns an <code>Enumeration</code> of all the objects in
119       * this collection.
120       *
121       * @return an <code>Enumeration</code> of this collection's objects
122       */
123      public abstract Enumeration<Permission> elements();
124    
125      /**
126       * This method sets this <code>PermissionCollection</code> object to be
127       * read only.  No further permissions can be added to it after calling this
128       * method.
129       */
130      public void setReadOnly()
131      {
132        readOnly = true;
133      }
134    
135      /**
136       * This method tests whether or not this <code>PermissionCollection</code>
137       * object is read only.
138       *
139       * @return true if this collection is read only
140       */
141      public boolean isReadOnly()
142      {
143        return readOnly;
144      }
145    
146      /**
147       * This method returns a <code>String</code> representation of this
148       * collection.  It is formed by:
149       * <pre>
150       * super.toString()" (\n"
151       *   // enumerate all permissions, one per line
152       * ")\n"
153       * </pre>
154       *
155       * @return a <code>String</code> representing this object
156       */
157      public String toString()
158      {
159        StringBuffer sb = new StringBuffer(super.toString());
160    
161        sb.append(" (\n");
162        Enumeration<Permission> e = elements();
163        while (e.hasMoreElements())
164          sb.append(' ').append(e.nextElement()).append('\n');
165        return sb.append(")\n").toString();
166      }
167    } // class PermissionCollection